# Patent

## Title
Developing device, and image forming apparatus and process cartridge incorporating same

## Abstract

An image forming apparatus includes a latent image bearer having a shaft to rotate in a normal direction for image formation and a reverse direction, a charging device, a latent image forming device, a developing device including a developer bearer having a shaft, a driving source, a drive transmission device to transmit a driving force from the driving source to the shaft of the latent image bearer and the shaft of the developer bearer. The developer bearer rotates in a predetermined direction during image formation and transports developer including toner to a developing range facing the latent image bearer, thereby developing the latent image on the latent image bearer. The drive transmission device is configured to inhibit transmission of the driving force to the shaft of the developer bearer when the latent image bearer rotates in the reverse direction.

## Background
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 No. 2015-100738, filed on May 18, 2015, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.
BACKGROUND
Technical Field
Embodiments of the present invention generally relate to a developing device, and a process cartridge and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction peripheral (MFP or multifunction machine) having at least two of copying, printing, facsimile transmission, plotting, and scanning capabilities, that include the developing device.
Description of the Related Art
There are image forming apparatuses in which a photoconductor serving as a latent image bearer and a developing roller serving as a developer bearer are driven by an identical driving motor (i.e., a single driving source).
SUMMARY
An embodiment of the present invention provides an image forming apparatus that includes a latent image bearer having a shaft to rotate in a normal direction for image formation and a reverse direction to the normal direction, a charging device to charge a surface of the latent image bearer, a latent image forming device to form a latent image on the latent image bearer, a developing device including a developer bearer having a shaft, a driving source, a drive transmission device to transmit a driving force from the driving source to the shaft of the latent image bearer and the shaft of the developer bearer. The developer bearer rotates in a predetermined direction during image formation and transports developer including toner to a developing range facing the latent image bearer, thereby developing the latent image on the latent image bearer. The drive transmission device is configured to inhibit transmission of the driving force to the shaft of the developer bearer when the latent image bearer rotates in the reverse direction.
In another embodiment, a developing device for an image forming apparatus includes the above-described developer bearer, a casing to contain the developer and accommodate the developer bearer, and a one-way clutch attached to the shaft of the developer bearer. The casing has an opening via which an inside of the casing communicates with the developing range. The one-way clutch inhibits transmission of a driving force from a driving source to the shaft of the developer bearer when the latent image bearer of the image forming apparatus rotates in a reverse direction to a normal direction for image formation.
Yet another embodiment provides a process cartridge to be removably installed in an image forming apparatus. The process cartridge includes the latent image bearer to bear the latent image, the above-described developing device to develop the latent image on the latent image bearer, and a common holder to hold the latent image bearer and the developing device as a single unit.



BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
A more complete appreciation of the disclosure and many of the 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 perspective view illustrating a drive transmission device for an image forming unit according to an embodiment;
FIG. 2 is a cross-sectional view illustrating a drive transmission mechanism for a developing device in the image forming unit illustrated in FIG. 1;
FIG. 3A is a perspective view illustrating a state of drive transmission to the developing device during image formation;
FIG. 3B is a perspective view illustrating a state of the drive transmission while a photoconductor rotates in a reverse direction to inhibit defective cleaning of the photoconductor;
FIG. 4 is a schematic cross-sectional view illustrating an image forming apparatus including the image forming unit illustrated in FIG. 1;
FIG. 5 is an enlarged view of an image forming unit according to an embodiment;
FIG. 6 is a cross-sectional view of the image forming unit;
FIG. 7A is a perspective view of the image forming unit;
FIG. 7B is another perspective view of the image forming unit;
FIG. 7C is a perspective view of the image forming unit from which a casing of a photoconductor cleaning device is removed; and
FIG. 8 is a schematic view illustrating generating of sucking-in airflow in a developing device.



DETAILED DESCRIPTION
In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, an image forming apparatus 100 according to an embodiment of the present invention is described. For example, the image forming apparatus 100 is a copier.
FIG. 4 is a schematic cross-sectional view illustrating the image forming apparatus 100 including a developing device 12 according to the present embodiment.
Referring to FIG. 4, a configuration of the image forming apparatus 100 is described.
The image forming apparatus 100 includes an exposure glass 101 on which a document is placed, an optical reading device 102 to scan an image on the document, an image forming unit 1 including a photoconductor 10, and a sheet feeder disposed in a lower section of the image forming apparatus 100.
When a user presses a start button of the image forming apparatus 100, the optical reading device 102 scans an image on the document, and, simultaneously, the sheet feeder feeds a sheet P of recording media from the lower section to a position between the photoconductor 10 and a transfer device 13 as indicated by arrows in FIG. 4. The photoconductor 10 rotates counterclockwise in FIG. 4
The image forming unit 1 includes a charging device 11 disposed facing the photoconductor 10 to uniformly charge the surface of the photoconductor 10, a developing device 12 to develop a latent image, and a photoconductor cleaning device 15.
The image forming apparatus 100 further includes an optical writing device 103 to direct a laser beam L onto the surface of the photoconductor 10, thereby forming an electrostatic latent image thereon, corresponding to the scanned image of the document. The optical writing device 103 serves as a latent image forming device.
As the photoconductor 10 rotates downstream in the direction indicated by an arrow, the electrostatic latent image on the photoconductor 10 passes through a developing range, where the photoconductor 10 faces a developing roller 12d (in FIG. 5) of the developing device 12. The developing roller 12d bears developer including toner and carrier. In the developing range, the toner in the developer on the developing roller 12d adheres to the photoconductor 10, thereby sequentially developing the electrostatic latent image into a visible image (i.e., a toner image).
The transfer device 13 transfers the toner image onto the sheet P, which is fed to the position between the photoconductor 10 and the transfer device 13 as described above.
The image forming apparatus 100 further includes a sheet separator 14 and a fixing device 104. The sheet separator 14 discharges electricity (attenuates electrical charges) to separate, from the photoconductor 10, the sheet P electrostatically adhering to the photoconductor 10. The fixing device 104 fixes the image on the sheet P, after which the sheet P is ejected to an output tray 105. Alternatively, instead of the sheet separator 14, the image forming apparatus 100 includes a stripping claw to mechanically separate the sheet P from the photoconductor 10.
A cleaning blade 15a of a photoconductor cleaning device 15 removes toner remaining on the photoconductor 10, and a discharge lamp initialize the surface potential of the photoconductor 10. At least two of the photoconductor 10, the charging device 11, the developing device 12, and the photoconductor cleaning device 15 can are united together into a process cartridge.
In FIG. 4, a reference numeral 200 represents a driving source to rotate the photoconductor 10 and a developing sleeve 12d-2 of the developing roller 12d. 
FIG. 5 is an enlarged view of the image forming unit 1.
In the configuration illustrated in FIG. 5, the image forming unit 1 includes the photoconductor 10, the charging device 11, the developing device 12, and the photoconductor cleaning device 15, which are supported by a common holder 1A (illustrated in FIG. 6) as a single unit (i.e., a process cartridge). The image forming unit 1 is removably installable in the body of the image forming apparatus 100. In the image forming unit 1, the charging device 11, the developing device 12, and the photoconductor cleaning device 15 are disposed around the photoconductor 10. In the image forming unit 1 according to the present embodiment, the charging device 11 employs a charging roller 11a, and the photoconductor cleaning device 15 employs the cleaning blade 15a to clean the surface of the photoconductor 10. The photoconductor cleaning device 15 includes a conveyor 15b to transport the toner (i.e., residual toner) collected by the cleaning blade 15a, and the collected toner is transported to the outside of the photoconductor cleaning device 15. The collected toner is transported from the photoconductor cleaning device 15 to the developing device 12 and reused (or recycled) in image developing.
Image forming operations of the image forming apparatus 100 is described below with reference to FIGS. 4 and 5.
The document is placed on the exposure glass 101. When the start button is pressed in this state, the optical reading device 102 optically reads image data of the document set on the exposure glass 101.
More specifically, the optical reading device 102 scans the image on the document on the exposure glass 101 with light emitted from an illumination lamp. The light reflected from the surface of the document is imaged on a sensor via mirrors and lenses. The image data of the document read by the sensor is converted into electrical image signals.
Then, the image data is transmitted to the optical writing device 103 (i.e., an exposure device). Then, the optical writing device 103 directs a laser beam L to the photoconductor 10 according to image data.
The photoconductor 10 rotates in the direction indicated by arrow YA illustrated in FIG. 5. The surface of the photoconductor 10 is charged uniformly at a position facing the charging roller 11a of the charging device 11 (a charging process). Then, the surface of the photoconductor 10 has a predetermined charge potential. Subsequently, the surface of the photoconductor 10 thus charged reaches a position to receive the laser beam L. The optical writing device 103 emits the laser beam L from a light source according to the image signals (exposure process).
A polygon mirror rotating at high speed deflects the laser beam L in the direction of a rotation axis of the photoconductor 10 (i.e., a main scanning direction) so that the laser beam L scans the surface of the photoconductor 10. Thus, an electrostatic latent image is formed on the photoconductor 10 charged by the charging device 11.
Subsequently, the surface of the photoconductor 10 bearing the electrostatic latent image reaches a position facing the developing device 12. The developing device 12 contains two-component developer including toner (toner particles) and carrier (carrier particles) and supplies the toner to the surface of the photoconductor 10, thereby developing the latent image thereon into a toner image (development process). Then, the surface of the photoconductor 10 reaches a position to face the sheet P. At that position, the transfer device 13 including a transfer bias charger is disposed to contact or abut with a back side of the sheet P. The transfer bias charger and the photoconductor 10 facing the transfer bias charger via the sheet together form a transfer section. In the transfer section, the toner image on the photoconductor 10 is transferred onto the sheet P (transfer process). It is to be noted that, instead of the transfer bias charger, a transfer bias roller can be used.
Subsequently, the surface of the photoconductor 10 reaches a position facing the photoconductor cleaning device 15, where the cleaning blade 15a collects the toner (i.e., untransferred toner) remaining on the photoconductor 10 (cleaning process).
Subsequently, the surface of the photoconductor 10 passes through a discharge section, where electrical potentials remaining on the surface of the photoconductor 10 are removed. Thus, a sequence of image forming processes performed on the photoconductor 10 is completed, and the photoconductor 10 is prepared for subsequent image formation.
The photoconductor cleaning device 15 includes the conveyor 15b to transport the toner (i.e., residual toner) and the like collected by the cleaning blade 15a to the outside of the photoconductor cleaning device 15. The collected toner is transported from the photoconductor cleaning device 15 to the developing device 12 and reused in image developing. The sheet P to which the toner image is transferred in the transfer section is sent to the fixing device 104. In the fixing device 104, a fixing belt and a pressing roller are pressed against each other, forming a fixing nip, where the toner image is fixed on the sheet P with heat and pressure. Then, the sheet P is transported by a pair of discharge rollers and stacked on the output tray 105. Then, a sequence of image forming processes is completed.
As illustrated in FIG. 5, the developing device 12 includes a casing 12a that includes a lower case 12b and an upper case 12c. 
FIG. 6 is an enlarged cross-sectional view of the image forming unit 1. FIG. 7A is a perspective view of the image forming unit 1. FIG. 7B is a perspective view of the image forming unit 1 as viewed from a different angle. FIG. 7C is a perspective view of the image forming unit 1 from which a casing of the photoconductor cleaning device 15 is removed.
In FIG. 7C, the conveyor 15b transports the collected toner (i.e., residual toner and the like collected by the cleaning blade 15a) in the longitudinal direction of the photoconductor cleaning device 15 and discharges the collected toner outside the photoconductor cleaning device 15. Specifically, the collected toner drops down at the end (the distal side in FIG. 7C) in the longitudinal direction of the photoconductor cleaning device 15 and passes through a space inside an inclined container at the end (the proximal side in FIG. 7A) in the longitudinal direction. Then, the collected toner is transported to the developing device 12 and reused in image developing.
In FIGS. 5 and 6, the developing device 12 includes the developing roller 12d serving as a developer bearer disposed facing the photoconductor 10, developer conveyors, namely, a supply screw 12f and a conveying screw 12e (a stirring and conveying member), a doctor blade 12g serving as a developer regulator, and a partition 12h. Each of the supply screw 12f and the conveying screw 12e includes a rotation shaft and a spiral blade winding around the rotation shaft and transports, by rotation, the developer in an axial direction (longitudinal direction) thereof.
The developing roller 12d includes a magnet roller 12d-1 including multiple stationary magnets and the developing sleeve 12d-2 that rotates around the magnet roller 12d-1. Although the magnet roller 12d-1 includes the multiple magnets, the magnet roller 12d-1 is depicted as a single component in FIG. 6 for simplicity. The developing sleeve 12d-2 contains the developing sleeve 12d-2 and is a rotatable, cylindrical member made of a nonmagnetic material.
The magnet roller 12d-1 has multiple magnetic poles, for example, five magnetic poles of: a first pole (north pole or N pole) disposed facing the developer regulator; a second pole (south pole or S pole) disposed facing the photoconductor 10; a third pole (N pole) serving as a conveyance pole disposed facing the upper case 12c downstream from the second pole in the direction of rotation of the developing sleeve 12d-2; a fourth pole (N pole) disposed downstream from the third pole in the direction of rotation of the developing sleeve 12d-2; and a fifth pole (S pole) disposed downstream from the fourth pole in the direction of rotation of the developing sleeve 12d-2 and serving as a developer scooping pole. In a range from the third pole (N pole) and the fourth pole (N pole), the developer is separated from the developing roller 12d and falls to the lower case 12b. 
The casing 12a of the developing device 12 contains two-component developer including toner and carrier (one or more additives can be included).
The supply screw 12f and the conveying screw 12e transport developer in the longitudinal direction (the direction along a rotation shaft 12l of the developing sleeve 12d-2 illustrated in FIGS. 1 and 2,) to form a circulation passage inside the developing device 12. The supply screw 12f and the conveying screw 12e are disposed side by side in a lateral direction in FIG. 6, and a supply compartment and a stirring compartment are formed with the partition 12h disposed between the conveying screw 12e and the supply screw 12f. 
Additionally, in the upper case 12c, the doctor blade 12g is disposed upstream in the direction of rotation of the developing sleeve 12d-2 from the developing range, where the developing sleeve 12d-2 faces the photoconductor 10. The doctor blade 12g is disposed approximately horizontal in the normal direction of the developing roller 12d and adjusts the amount of developer, borne on the developing sleeve 12d-2, conveyed to the developing range.
Toner is supplied into the developing device 12 from a toner supply inlet 12p (illustrated in FIGS. 3A and 3B) disposed above the conveying screw 12e and at the end in the longitudinal direction of the conveying screw 12e. The collected toner (hereinafter also “reused toner”) is supplied from a reuse toner inlet 12q disposed on the left of the toner supply inlet 12p in FIGS. 3A and 3B. The supplied toner and the reused toner, together with the developer in the developing device 12, are transported in the opposite directions by the conveying screw 12e and the supply screw 12f, stirred together, and circulated. The supply screw 12f supplies a portion of the developer thus stirred to the surface of the developing sleeve 12d-2 serving as the developer bearer, and the developer is carried thereon. After the doctor blade 12g adjusts the amount of developer carried on the developing sleeve 12d-2, the developer is transported to the developing range. In the developing range, the toner in developer on the developing sleeve 12d-2 adheres to the latent image on the surface of the photoconductor 10, developing the latent image.
The developing device 12 is filled with the developer in which the toner and the carrier (i.e., magnetic particles) are mixed uniformly. The conveying screw 12e and the supply screw 12f disposed side by side laterally rotate to transport the developer and simultaneously agitate the developer with fresh toner supplied through the toner supply inlet 12p. Thus, the toner and carrier are mixed uniformly, and charge potentials are given to the toner.
While transporting the uniformly mixed developer in the longitudinal direction, the supply screw 12f adjacent to and parallel to the developing sleeve 12d-2 supplies the developer to the developing sleeve 12d-2. Then, the magnetic force exerted by the fifth pole (the developer scooping pole) of the magnet roller 12d-1 inside the developing sleeve 12d-2 attracts the developer to the outer surface of the developing sleeve 12d-2. As the developing sleeve 12d-2 rotates clockwise as indicated by arrow YB illustrated in FIG. 6, the developer carried thereon is adjusted by the doctor blade 12g and transported to the developing range. A developing bias voltage is applied to the developing sleeve 12d-2, and thus a developing electrical field is generated between the developing sleeve 12d-2 and the photoconductor 10 in the developing range. The developing electrical field promotes the supply of toner from the surface of the developing sleeve 12d-2 to the surface of the photoconductor 10, thereby developing the latent image on the photoconductor 10. The developer on the developing sleeve 12d-2 that has passed through the developing range is collected in the supply compartment inside the developing device 12 as the developing sleeve 12d-2 rotates. That is, the developer is supplied from the supply compartment to the developing sleeve 12d-2, and the developer on the developing sleeve 12d-2 that has passed through the developing range is collected in the supply compartment. The supplying and the collecting occur in the entire span of the supply compartment in the longitudinal direction thereof.
While the supply screw 12f transports the developer in the supply compartment, a constant amount of developer is scooped from the supply compartment onto the surface of the developing sleeve 12d-2 by the rotation of the supply screw 12f as well as the magnetic force exerted from the fifth pole serving as the developer scooping pole. After adjusted by the doctor blade 12g, the developer on the developing sleeve 12d-2 passes through the developing range and reaches a position of a developer release pole formed by the third and fourth magnetic poles adjacent to each other, having the same polarity (N pole). The developer is separated from the developing sleeve 12d-2 by the magnetic force exerted from the developer release pole and is collected in the supply compartment.
The supply screw 12f in the supply compartment transports the developer separated from the developing sleeve 12d-2 at the developer release position in the axial direction of the supply screw 12f and in the direction opposite to the direction in which the conveying screw 12e transports the developer. Through a first communicating opening, the downstream end of the supply compartment in which the supply screw 12f is disposed communicates with the upstream end of the stirring compartment in which the conveying screw 12e is disposed. At the downstream end of the supply compartment, the developer is pushed out the first communicating opening by the developer transported from behind. Then, the developer reaches the upstream end of the stirring compartment. As the conveying screw 12e inside the stirring compartment rotates, the developer is transported to the downstream end of the stirring compartment.
The upstream end of the supply compartment communicates with the downstream end of the stirring compartment via a second communicating opening. The developer transported to the downstream end of the stirring compartment passes through the second communicating opening to the upstream end of the supply compartment.
As the developer is transported from the downstream end of the supply compartment to the stirring compartment and further from the downstream end of the stirring compartment to the supply compartment, the developer circulates inside the developing device 12.
The amount of developer in the supply compartment decreases toward the downstream side in the developer conveyance direction since the developer is scooped up to the developing roller 12d while being transported by the supply screw 12f. In the supply compartment, the supply screw 12f further collects and transports the developer that has passed through the developing range and left the developing sleeve 12d-2, and the amount of developer therein increases toward the downstream side in the developer conveyance direction. Accordingly, the amount of developer in the supply compartment is almost equal between the upstream side and the downstream side.
The toner supply inlet 12p is disposed at the upstream end of the stirring compartment, and fresh toner is supplied from a toner container via a toner supply device and a toner hopper to the toner supply inlet 12p as required. Thus, in the stirring compartment, the conveying screw 12e stirs and transports a small amount of developer supplied, as required, from the toner supply inlet 12p and a small amount of reused toner supplied from the reuse toner inlet 12q, together with the developer in the stirring compartment, and the amount of developer therein is kept almost equal between the upstream side and the downstream side. Accordingly, in circulating the developer (the carrier in particular) in the stirring compartment and the supply compartment, fluctuations in the amount of developer are inhibited, thereby securing uniform circulation.
As described above, in the developing device 12, the supply screw 12f and the conveying screw 12e rotate, and simultaneously the developer is attracted to the developing sleeve 12d-2 by the magnetic attraction exerted by the magnet roller 12d-1. Additionally, the developing sleeve 12d-2 is rotated at a predetermined speed ratio to the speed of the photoconductor 10 to scoop the developer to the developing range consecutively. The developer is separated from the developing sleeve 12d-2 by the developer release pole formed by the third and fourth poles generating a repulsive magnetic force. The developer transported to the area in which the repulsive magnetic force is exerted is released in the composite direction of the direction normal to the developing sleeve 12d-2 and the direction tangential to the rotation of the developing sleeve 12d-2. Then, the developer is collected in the supply compartment.
In some cases, the photoconductor 10 is rotated in the direction reverse to a normal direction for image formation. In the image forming apparatus 100, in removal of the untransferred toner remaining on the photoconductor 10, a rotation shaft 10b (illustrated in FIG. 2) of the photoconductor 10 is rotated in the direction reverse to the normal direction for image formation.
The photoconductor and the developing roller can be driven by an identical driving motor, as in the present embodiment. In such a configuration, if the rotation shaft of the developing roller rotates in the direction reverse as the photoconductor rotates in the revere direction, inconveniences may arise.
Specifically, in developing devices employing two-component developer including toner and carrier, typically, the two-component developer is caused to stand on end on the surface of the developing sleeve containing multiple magnetic poles, thereby generating a magnetic brush. As the developing roller rotates, the magnetic brush thereon contacts the electrostatic latent image on the surface of the photoconductor in the developing range. Then, due to an electrostatic attraction between the magnetic brush and the electrostatic latent image, the toner in the developer moves to the electrostatic latent image.
FIG. 8 is a schematic view illustrating air sucked in the casing 12a as the developing roller 12d rotates.
Referring to FIG. 8, the casing 12a includes an opening 22 through which the inside of the casing 12a communicates the developing range. That is, the developing roller 12d accommodated in the casing 12a is exposed through the opening 22.
In FIG. 8, during image formation, the developing roller 12d (the developing sleeve 12d-2 in particular) rotates in the normal direction indicated by arrow YB. Downstream from the developing range, the tip of the magnetic brush (i.e., developer G) contacts the casing 12a while moving in the direction indicated by arrow YB. This movement causes sucking-in airflow that flows in the direction indicated by arrow YC in FIG. 8, into the casing 12a (i.e., a developer container) through an opening 22, and the developer G is collected through the opening 22 in the casing 12a. With the sucking-in airflow, floating developer (toner in particular), which has escaped from the rotation of the developing roller 12d, and the toner on the developing roller 12d downstream from the developing range is collected in the casing 12a. 
Reverse rotation of the photoconductor 10 is described below.
While the cleaning blade 15a keeps collecting the residual toner, paper fibers, dust, or the like (i.e., residual materials) from the photoconductor 10, it is possible that the residual materials accumulate on the upstream side of the cleaning blade 15a in the direction of rotation of the photoconductor 10, and the residual materials enter the gap between end of the cleaning blade 15a and the surface of the photoconductor 10. That is, cleaning becomes defective. In view of the foregoing, the photoconductor 10 is rotated in reverse to draw away the residual materials from the cleaning blade 15a. Subsequently, the photoconductor 10 is rotated in the normal direction for image formation to collect the residual materials with the cleaning blade 15a properly contacting the surface of the photoconductor 10.
If the developing roller 12d is rotated in the reverse direction as well when the photoconductor rotates in the reverse direction for inhibiting defective cleaning of the photoconductor, the following inconvenience may arise. While the developing roller 12d rotates in the reverse direction, in the opening 22, flowing-out airflow flowing to the outside of the casing 12a is generated. It is possible that, transported by the flowing-out airflow, the toner leaks outside the casing 12a and adheres to the casing 12a of the developing device or the holder 1A of the image forming unit 1, for example.
Next, features of the present embodiment are described in further detail below.
FIG. 1 is a perspective view illustrating a drive transmission device for the image forming unit 1. FIG. 2 is a cross-sectional view of drive transmission for the developing device 12. FIG. 3A is a perspective view illustrating the drive transmission to the developing device 12 during image formation. FIG. 3B is a perspective view illustrating the drive transmission while the photoconductor 10 rotates in reverse to inhibit defective cleaning of the photoconductor 10.
In a center hollow 10a inside the cylindrical photoconductor 10 illustrated in FIG. 1, a rotation shaft 10b of the photoconductor 10 is fitted to engage therewith. As illustrated in FIG. 2, a photoconductor driving gear 10c is attached to the rotation shaft 10b of the photoconductor 10. The photoconductor driving gear 10c transmits the driving force to a developing driving gear 12i from the driving source 200 illustrated in FIG. 4, which is a driving motor such as a direct-current (DC) servo, a stepping motor, or the like. The rotation shaft 10b of the photoconductor 10 is fitted in a center of the photoconductor driving gear 10c to engage therewith. Internal teeth on the inner circumference of the photoconductor driving gear 10c mesh with external teeth of the developing driving gear 12i. A developing driving input gear 12j is disposed coaxially with the developing driving gear 12i, and external teeth of the developing driving input gear 12j mesh with external teeth at the outer circumference of a developing sleeve gear 12k. The developing sleeve gear 12k is attached to a rotation shaft 12l of the developing sleeve 12d-2.
The developing sleeve gear 12k contains a one-way clutch 12m illustrated in FIG. 1. The one-way clutch 12m is a clutch to transmit rotation only in a predetermined direction. When the developing sleeve gear 12k rotates in a first direction for image formation, the one-way clutch 12m meshes with the rotation shaft 12l of the developing sleeve 12d-2. When the developing sleeve gear 12k rotates in a second direction reverse to the first direction for image formation, the one-way clutch 12m does not mesh with the rotation shaft 12l of the developing sleeve 12d-2. Then, the developing sleeve gear 12k and the one-way clutch 12m rotate idle.
A conveying-screw driving gear 12o is disposed on the rotation shaft of the conveying screw 12e illustrated in FIG. 6. A supply-screw driving gear 12n is disposed on the rotation shaft of the supply screw 12f illustrated in FIG. 6. It is to be noted that the one-way clutch 12m can be contained in an intermediate gear in the transmission gear train between an output shaft of the driving source 200 (e.g., the driving motor) and the rotation shaft 12l of the developing sleeve 12d-2. For example, the one-way clutch 12m can be contained the developing driving input gear 12j serving as the intermediate gear to transmit the driving force of the driving motor to the rotation shaft 12l of the developing sleeve 12d-2.
The photoconductor driving gear 10c, the developing driving gear 12i, the developing driving input gear 12j, the developing sleeve gear 12k, and the one-way clutch 12m together serve as the drive transmission device to transmit the driving force from the driving source 200 to the shaft of the latent image bearer (the photoconductor 10) and the shaft of the developer bearer (the developing sleeve 12d-2).
Descriptions are given below of drive transmission to the developing device 12 during image formation and during reverse rotation of the photoconductor 10 to inhibit defective cleaning, with reference to the drawings.
In the drive transmission device for the developing device 12, during image formation, as the photoconductor driving gear 10c illustrated in FIG. 2 rotates in the direction for image formation, the developing driving gear 12i (illustrated in FIG. 1) meshing with the photoconductor driving gear 10c rotates. The developing driving input gear 12j, which is disposed on the identical shaft to which the developing driving gear 12i is disposed, rotates in the direction indicated by arrow A (hereinafter “rotation direction A”) illustrated in FIG. 3A. This rotation is transmitted to the developing sleeve gear 12k meshing with the developing driving input gear 12j, and the developing sleeve gear 12k rotates in the direction indicated by arrow B (hereinafter “rotation direction B”) illustrated in FIG. 3A.
The one-way clutch 12m contained in the developing sleeve gear 12k rotates in the direction indicated by arrow C (hereinafter “rotation direction C”) in FIG. 3A, which is identical to the rotation direction B of the developing sleeve gear 12k. The one-way clutch 12m meshes with the rotation shaft 12l of the developing sleeve 12d-2, and the rotation shaft 12l of the developing sleeve 12d-2 rotates in the rotation direction C in FIG. 3A, together with the one-way clutch 12m. Accordingly, the developing sleeve 12d-2 rotates.
It is to be noted that, as the supply-screw driving gear 12n meshing with the developing driving input gear 12j rotates in the direction indicated by arrow D (hereinafter “rotation direction D”) in FIG. 3A, the supply screw 12f rotates. The conveying-screw driving gear 12o rotates in the direction identical to the rotation direction D of the supply-screw driving gear 12n, via an idle gear between the supply-screw driving gear 12n and the conveying-screw driving gear 12o. 
By contrast, when the photoconductor 10 is rotated in reverse to inhibit defective cleaning of the photoconductor 10, the drive transmission device according to the present embodiment operates as follows.
As the photoconductor driving gear 10c illustrated in FIG. 2 rotates in the direction reverse to the normal direction for image formation, the developing driving gear 12i (illustrated in FIGS. 1 and 2), which meshes with the photoconductor driving gear 10c, rotate in the direction reverse to the rotation direction A illustrated in FIG. 3A. Then, the developing driving input gear 12j, which is disposed on the identical shaft to which the developing driving gear 12i is disposed, rotates in the direction indicated by arrow E (hereinafter “rotation direction E”) illustrated in FIG. 3B. This rotation is transmitted to the developing sleeve gear 12k meshing with the developing driving input gear 12j, and the developing sleeve gear 12k rotates in the direction indicated by arrow F (hereinafter “rotation direction F”) illustrated in FIG. 3B.
At that time, the one-way clutch 12m does not mesh with the rotation shaft 12l of the developing sleeve 12d-2, and the developing sleeve gear 12k and the one-way clutch 12m rotate idle. As a result, the rotation shaft 12l of the developing sleeve 12d-2 does not rotate.
It is to be noted that the supply-screw driving gear 12n meshing with the developing driving input gear 12j rotates in the direction indicated by arrow H (hereinafter “rotation direction H”) in FIG. 3B.
With this configuration, when the photoconductor 10 rotates in the direction reverse to the normal direction for image formation, the rotation shaft 12l of the developing sleeve 12d-2 does not rotate. Accordingly, the flowing-out airflow, which is generated by reverse rotation of the developing sleeve 12d-2, does not occur in the present embodiment, thereby inhibiting the leak of developer from the casing 12a (the developer container) of the developing device 12.
Further, in the present embodiment, even when the developing sleeve 12d-2 is kept stationary, the supply screw 12f and the conveying screw 12e are rotated in reverse to stir the developer, thereby securing toner charge. Thus, insufficient charge of toner in subsequent image formation is inhibited. Although the reverse rotation of the supply screw 12f and the conveying screw 12e cause slight airflow in the developing device 12, the developer on the developing sleeve 12d-2, which is not rotating, is retained in the gap between the upper case 12c (in FIG. 6) and the developing sleeve 12d-2 due to the magnetic force exerted by the third magnetic pole of the developing sleeve 12d-2. Accordingly, the airflow inside the developing device 12 does not become the flowing-out airflow at the opening 22 illustrated in FIG. 8.
It is to be noted that the configuration to inhibit transmission of the driving force to the shaft of the developer bearer is not limited to the one-way clutch 12m. Alternatively, for example, one (e.g., the developing sleeve gear 12k) of the gears disposed between the photoconductor driving gear 10c and the rotation shaft 12l of the developing sleeve 12d-2 may be moved in the axial direction to disconnect the drive transmission to the rotation shaft 12l of the developing sleeve 12d-2 during reverse rotation of the photoconductor 10.
It is to be noted that the inconveniences caused by the reverse rotation of the developer bearer can occur also in configurations in which generation of the sucking-in airflow during image formation is inhibited.
The various aspects of the present specification can attain specific effects as follows.
Aspect A
A developing device includes a developer bearer, such as the developing roller 12d, to bear developer on a surface thereof and transport, by rotation, the developer to a developing range facing a latent image bearer, such as the photoconductor 10. In the developing range, the developer bearer supplies the developer to a latent image on the latent image bearer. When a rotation shaft of the latent image bearer rotates in a direction reverse to a normal direction for image formation, receiving a driving force from a driving source, the driving force from the driving source is not transmitted to a rotation shaft of the developer bearer.
According to this aspect, when the rotation shaft of the latent image bearer rotates in the direction reverse to the normal direction for image formation, the rotation shaft of the developer bearer does not rotate. Therefore, the inconveniences caused by the reverse rotation of the developer bearer are inhibited.
Aspect B
The developing device according to Aspect A further includes a casing 12a serving as a developer container to contain the developer supplied to the surface of the developer bearer, and the developer bearer is disposed in the casing 12a. The casing includes an opening 22 to make the inside of the casing communicate with the developing range and generate airflow flowing to the inside of the casing as the rotation shaft of the developer bearer rotates in the normal direction for image formation. With the airflow, toner is collected inside the casing.
As described above, the photoconductor is rotated in reverse, for example, to inhibit defective cleaning of the photoconductor. However, if the developer bearer rotates in the reverse direction together with the photoconductor rotating in the revere direction, it is possible that air flows out the casing 12a through the opening 22. In this case, it is possible that the toner leaks outside the casing, being transported by the flowing-out airflow.
According to this aspect, when the rotation shaft of the latent image bearer rotates in the direction reverse to the normal direction for image formation, rotation driving is not transmitted to the rotation shaft of the developer bearer, and accordingly the developer bearer does not rotate in the direction reverse to the direction for image developing. Therefore, in the opening, the flowing-out airflow does not occur. Accordingly, the developer is inhibited from leaking through the opening.
Aspect C
In Aspect A or B, the drive transmission device includes a one-way clutch 12m to rotate only in the direction in which the rotation shaft of the developer bearer rotates for image formation. The one-way clutch 12m is disposed in a drive transmission train to transmit a driving force from the driving source to the rotation shaft of the developer bearer.
According to this aspect, with a simple structure, the drive transmission device can be configured not to transmit the driving force to the rotation shaft of the developer bearer when the rotation shaft of the latent image bearer rotates in the direction reverse to the normal direction for image formation. Thus, the cost of the drive transmission device can be lower.
Aspect D
In Aspect C, the one-way clutch is attached to the rotation shaft of the developer bearer.
According to this aspect, compared with an arrangement in which the one-way clutch is disposed between the rotation shaft of the developer bearer and the output shaft of the driving source, the space to accommodate the one-way clutch is reduced, and the device can be kept compact.
Aspect E
An image forming apparatus includes, at least, the latent image bearer to bear an electrostatic latent image thereon, a charging device to charge the surface of the latent image bearer, a latent image forming device to form the electrostatic latent image on the latent image bearer, and the developing device, according to any one of Aspects A through C, to develop the electrostatic latent image.
According to this aspect, even when the rotation shaft of the latent image bearer rotates in the direction reverse to the normal direction for image formation, the rotation shaft of the developer bearer does not rotate, and accordingly leak of developer caused by the reverse rotation of the developer bearer is inhibited. Accordingly, the interior of the image forming apparatus is protected from contamination with the leaked developer.
Aspect F
Aspect N: A process cartridge that is removably installable in an apparatus body of an image forming apparatus includes at least the latent image bearer to bear a latent image, the developing device according to any one of Aspects A through C, and a common holder to hold those components.
According to this aspect, even when the rotation shaft of the latent image bearer rotates in the direction reverse to the normal direction for image formation, the rotation shaft of the developer bearer does not rotate, and accordingly leak of developer caused by the reverse rotation of the developer bearer is inhibited. Accordingly, the interior of the process cartridge is protected from contamination with the leaked developer.
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 appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.

## Claims

1. An image forming apparatus comprising:
a latent image bearer having a shaft to rotate in a normal direction for image formation and a reverse direction to the normal direction;
a charging device to charge a surface of the latent image bearer;
a latent image forming device to form a latent image on the latent image bearer;
a developing device including a developer bearer having a shaft to rotate in a predetermined direction during image formation, the developer bearer to transport developer including toner to a developing range facing the latent image bearer to develop the latent image on the latent image bearer;
a driving source; and
a drive transmission device to transmit a driving force from the driving source to the shaft of the latent image bearer and the shaft of the developer bearer,
the drive transmission device to inhibit transmission of the driving force to the shaft of the developer bearer when the latent image bearer rotates in the reverse direction.

2. The image forming apparatus according to claim 1,
wherein the drive transmission device includes a one-way clutch disposed in a drive transmission train to transmit the driving force from the driving source to the shaft of the developer bearer, and
wherein the one-way clutch rotates the shaft of the developer bearer only in the predetermined direction.

3. The image forming apparatus according to claim 2,
wherein the one-way clutch is attached to the shaft of the developer bearer.

4. The image forming apparatus of claim 1, wherein:
the developing device further includes a developer conveyor to convey and stir the developer, and
when the latent image bearer rotates in reverse, the developer bearer is not driven, but the developer conveyor is driven.

5. A developing device comprising:
a developer bearer having a shaft to rotate in a predetermined direction during image formation, the developer bearer to transport developer including toner to a developing range facing a latent image bearer to develop a latent image on the latent image bearer;
a casing to contain the developer and accommodate the developer bearer, the casing having an opening via which an inside of the casing communicates with the developing range; and
a one-way clutch attached to the shaft of the developer bearer to inhibit transmission of a driving force from a driving source to the shaft of the developer bearer when the latent image bearer rotates in a reverse direction to a normal direction for image formation.

6. The image forming apparatus according to claim 5,
wherein, as the shaft of the developer bearer rotates in the predetermined direction, airflow flowing from outside into the casing is generated at the opening.

7. A process cartridge to be removably installed in an image forming apparatus, the process cartridge comprising:
the latent image bearer to bear the latent image;
the developing device according to claim 5 to develop the latent image on the latent image bearer; and
a common holder to hold the latent image bearer and the developing device as a single unit.