Image forming apparatus

An image forming apparatus includes a drive unit, an image bearing member, a developing unit, a support unit, an urging member, and a switching mechanism. The urging member generates an urging force for pivoting the support unit in an approaching direction in which a peripheral surface of a developing roller is moved toward a peripheral surface of the image bearing member. The switching mechanism switches the support unit between a first position (fitting position) and a second position (releasing position). The support unit includes: a second drive input section disposed coaxially with a pivot shaft and for receiving a rotational drive force from a drive output shaft of the drive unit; and a transmission mechanism for transmitting the rotational drive force to a first drive input section. The rotation direction of the rotational drive force is for rotation in a direction of pivoting the support unit in the approaching direction.

INCORPORATION BY REFERENCE

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2013-068842, filed Mar. 28, 2013. The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND

The present disclosure relates to image forming apparatuses provided with a mechanism for moving a developing roller closer to and away from an image bearing member.

Some image forming apparatuses (for example, printers and copiers) include a photosensitive drum (image bearing member) and a developing unit. In addition, a gap roller is provided near each axial edge of a developing roller. The photosensitive drum bears a toner image on its peripheral surface. The developing unit includes the developing roller. The developing roller supplies toner to the photosensitive drum. In the printing operation, the photosensitive drum and the developing roller are brought into the state where the respective peripheral surfaces are opposed to each other with a predetermined gap therebetween (the state where each gap roller abuts against a non-image forming region of the peripheral surface of the photosensitive drum). In for example maintenance or jam-handling, on the other hand, when the developing unit is pulled out of the main body of the apparatus, the photosensitive drum and the developing roller are brought into the state where the respective peripheral surfaces are away from each other so as not to damage the peripheral surfaces.

For example, an image forming apparatus is suggested that includes a pressure member to bring the peripheral surface of the developing roller closer to the peripheral surface of the photosensitive drum. The developing unit is disposed to be horizontally movable within the main body. The developing unit is provided with a pin member on a side wall thereof. The pin member is guided by a horizontally elongated slot. The developing unit is urged in a horizontal direction by the pressure member. The pressure member presses the peripheral surface of the developing roller toward the peripheral surface of the photosensitive drum. Upon release of the pressure exerted by the pressure member, the developing roller moves away from the photosensitive drum.

SUMMARY

An image forming apparatus according to one aspect of the present disclosure includes a main housing, a drive unit, an image bearing member, a developing unit, a support unit, an urging member, and a switching mechanism. The drive unit has a drive output shaft that generates a rotational drive force for axial rotation. The image bearing member is disposed in the main housing and has a peripheral surface for bearing a toner image. The developing unit is attached to the main housing to be detachable by pulling out. The developing unit includes: a developing roller that has a peripheral surface for carrying toner thereon and that supplies the toner to the image bearing member; and a first drive input section that supplies a rotational drive force to the developing roller. The support unit is supported by the main housing to be freely pivotable about an axis of a pivot shaft and places and supports the developing unit in position. The urging member generates an urging force for urging the support unit to pivot in one of pivoting directions about the pivot shaft. The one pivoting direction coincides with an approaching direction for moving the peripheral surface of the developing roller toward the peripheral surface of the image bearing member. The switching mechanism switches the position of the support unit supporting the developing unit. The switching is made between a first position in which the peripheral surface of the developing roller is located relatively close to the peripheral surface of the image bearing member and a second position in which the peripheral surface of the developing roller is located relatively away from the peripheral surface of the image bearing member. The support unit includes: a second drive input section that is disposed coaxially with the pivot shaft and that receives a rotational drive force from the drive output shaft; and a transmission mechanism that transmits the rotational drive force received by the second drive input section to the first drive input section. The rotational drive force generated by the drive output shaft is for rotation in a direction of pivoting the support unit in the approaching direction.

DETAILED DESCRIPTION

The following describes an embodiment of the present disclosure with reference to the accompanying drawings. In each figure, the Z1 direction corresponds to “up”, Z2 to “down”, Y1 to “rear”, Y2 to “front”, X1 to “right”, and X2 to “left”.

First, with reference toFIG. 1, the following describes a schematic configuration of an image forming apparatus1according to the embodiment of the present disclosure.FIG. 1is a perspective view of an appearance of the image forming apparatus1according to the embodiment of the present disclosure.

The image forming apparatus1is a monochrome or color printer having a copier function, for example. The image forming apparatus1includes a main housing10(the housing of the main body) having a boxlike shape. The main housing10includes a lower housing11, an upper housing12disposed above the lower housing11, a connecting housing13disposed between the lower housing11and the upper housing12. The connecting housing13constitutes a right face10R of the main housing10.

The lower housing11accommodates various units used for performing image forming processing on a sheet. The upper housing12accommodates a scanner that optically reads an image of an original document sheet. The scanner operates when the image forming apparatus1functions as a copier.

A front cover110covers the front face of the lower housing11. A sheet cassette14is disposed below the lower housing11to be freely detachable. The sheet cassette14stores a stack of sheets which are to be subjected to image forming processing.

The main housing10has an in-body paper ejection space15. The in-body paper ejection space15is a space surrounded by the upper face of the lower housing11, the lower face of the upper housing12, and the left face of the connecting housing13. Sheets having gone through image forming processing are ejected to the in-body paper ejection space15. The in-body paper ejection space15is provided at the bottom with an in-body paper ejection tray151for receiving sheets.

An operation panel16is attached to the front face of the upper housing12. The operation panel16receives user operation information input to the image forming apparatus1.

On the right face10R of the main housing10, a manual feed tray17is provided for manually feeding a sheet. The manual feed tray17can be freely opened and closed relative to the right face10R.

Next, mainly with reference toFIGS. 2 and 3, the following describes an internal configuration of the image forming apparatus1according to the embodiment of the present disclosure.FIG. 2is a cross sectional view of the internal configuration of the image forming apparatus1.FIG. 3is a perspective view showing the image forming apparatus1in the state where the front cover110is removed. In each ofFIGS. 2 and 3, the upper right half of the lower housing11and the connecting housing13are shown. The cross section shown inFIG. 2is taken along the right-and-left direction (X direction) of the image forming apparatus1.

The lower housing11accommodates units used for image forming. The units used for image forming include a drum unit21, an exposure unit22, a developing unit23, a toner container24, a fixing unit25, and a conveyance unit26. These units are disposed such that each unit can be separately pulled forward relative to the lower housing11(a housing frame111).

The drum unit21includes a photosensitive drum211(image bearing member), a charging device212, and a cleaning device214. The charging device212is disposed around the photosensitive drum211. The photosensitive drum211rotates about its axis. The photosensitive drum211bears an electrostatic latent image and a toner image on its peripheral surface. The charging device212uniformly charges the peripheral surface of the photosensitive drum211.

The exposure unit22emits laser light to the peripheral surface of the photosensitive drum211to form an electrostatic latent image.

The developing unit23includes a developing roller231. The developing roller231is disposed in proximity to the photosensitive drum211. The developing roller231supplies toner to the peripheral surface of the photosensitive drum211to develop the electrostatic latent image formed on the peripheral surface of the photosensitive drum211.

The toner container24replenishes toner to the developing unit23.

The conveyance unit26includes a transfer roller213pressed against the photosensitive drum211. The transfer roller213forms a transfer nip portion N1 with the photosensitive drum211. The transfer roller213transfers the toner image on the photosensitive drum211to the sheet.

At a downstream location near the transfer nip portion N1, a separator section215is disposed. The cleaning device214cleans the peripheral surface of the photosensitive drum211after the toner image transfer. The separator section215separates, from the photosensitive drum211, the sheet onto which the toner image is transferred in the transfer nip portion N1. The sheet thus separated is forwarded to the fixing unit25.

The fixing unit25includes a fixing roller251and a pressure roller252. The fixing roller251includes a heat source therein. The fixing roller251and the pressure roller252together form a fixing nip portion N2.

The fixing unit25applies heat and pressure through the fixing nip portion N2 to the sheet onto which the toner image has been transferred in the transfer nip portion N1. The sheet subjected to the fixing process (the application of heat and pressure) by the fixing unit25is ejected from a sheet ejecting outlet131into the in-body paper ejection tray151.

As shown inFIG. 2, a sheet conveyance path for conveying sheets is provided inside the main housing10. The sheet conveyance path includes a main conveyance path P1 leading to the sheet ejecting outlet131. The main conveyance path P1 extends in the up-and-down direction (Z direction) from a location near the bottom of the lower housing11to the connecting housing13via the transfer nip portion N1 and the fixing nip portion N2. In addition, a reverse conveyance path P2 is provided for conveying sheets in reverse for duplex printing. The reverse conveyance path P2 extends from the downstream end of the main conveyance path P1 to a location near the upstream end of the main conveyance path P1.

The sheet cassette14(seeFIG. 1) is provided with a sheet accommodating section for accommodating a stack of sheets. At a location near the top right of the sheet accommodating section, a pickup roller271and a paper feed roller pair272are disposed. The pickup roller271picks up sheets one by one from the topmost sheet in the stack. The paper feed roller pair272forwards the sheet picked up by the pickup roller271to the upstream end of the main conveyance path P1.

A registration roller pair273is disposed upstream from the transfer nip portion N1 in the main conveyance path P1. The registration roller pair273forwards the sheet to the transfer nip portion N1 with predetermined timing.

In the image forming apparatus1according to the present embodiment, the inner face (left face) and the outer face (right face) of the conveyance unit26together form the main conveyance path P1 and the reverse conveyance path P2. For example, an immediately upstream portion of the main conveyance path P1 from the transfer nip portion N1 is defined by the inner face of the conveyance unit26and a pre-transfer guide274opposed to the conveyance unit26. In addition to the transfer roller213described above, the conveyance unit26includes one roller in the registration roller pair273and one roller in a conveyance roller pair (not shown) for conveying a sheet in the reverse conveyance path P2.

The following describes an image forming operation of the image forming apparatus1mainly with reference toFIG. 2.

First, the charging device212charges the peripheral surface of the photosensitive drum211substantially uniformly. Next, the charged peripheral surface of the photosensitive drum211is exposed to laser light emitted by the exposure unit22. As a result, an electrostatic latent image conforming to image data (image to be formed on a sheet) is formed on the peripheral surface of the photosensitive drum211. Next, the developing unit23supplies toner to the peripheral surface of the photosensitive drum211. As a result, the toner image is visualized on the peripheral surface of the photosensitive drum211.

For example, in the single-side printing process, a sheet is fed from the sheet cassette14(seeFIG. 1) or the manual feed tray17to the main conveyance path P1. Next, the transfer nip portion N1 causes the toner image to be transferred to the sheet. Subsequently, the fixing nip portion N2 causes the transferred toner image to be fixed onto the sheet. The sheet onto which the toner image is fixed is ejected through the sheet ejecting outlet131into the in-body paper ejection tray151.

In the duplex printing process, on the other hand, the transfer and fixing processes described above are carried out on one side of the sheet. Then, when the sheet is partially ejected out of the sheet ejecting outlet131to the in-body paper ejection tray151, switch-back conveyance is executed to pull the sheet back. In detail, the sheet is brought back up to a location close to the upstream end of the main conveyance path P1 through the reverse conveyance path P2. Then, the other surface (unprinted surface) of the sheet is subjected to the transfer process and the fixing process. After the transfer and fixing processes on the both surfaces of the sheet, the sheet is ejected through the sheet ejecting outlet131onto the in-body paper ejection tray151.

The following describes operation of the image forming apparatus1when the developing unit23or the drum unit21is pulled out of the main housing10for maintenance or jam-handling for example, mainly with reference toFIG. 13.FIG. 13is a perspective view showing a rear side of a support unit30.

The image forming apparatus1according to the present embodiment further includes a mechanism for moving the peripheral surface of the photosensitive drum211and the peripheral surface of the developing roller231away from each other when the developing unit23or the drum unit21is pulled out of the main housing10. In detail, the developing roller231includes a pair of gap rollers23D. Each gap roller23D is disposed in proximity to an axial edge of the developing roller231. The photosensitive drum211has a non-image forming region211D on the peripheral surface along each axial edge. Such a mechanism ensures that the image forming apparatus1according to the present embodiment is less prone to damage on the respective peripheral surfaces of the photosensitive drum211and the developing roller231.

For example, at the time of image formation (hereinafter, referred to as “during normal operation”), the developing roller231and the photosensitive drum211are brought into a state where a predetermined gap (hereinafter, referred to as a first gap) between the respective peripheral surfaces. During the normal operation, each gap roller23D is urged against and in contact with the corresponding non-image forming region211D. Since the developing roller231is provided with the gap rollers23D, the first gap is secured between the peripheral surface of the developing roller231and the peripheral surface of the photosensitive drum211during the normal operation.

On the other hand, when the developing unit23or the drum unit21is pulled out of the main housing10for maintenance or jam-handling for example, the urging force against the gap rollers23D is released. As a consequence, the photosensitive drum211and the developing roller231are moved away from each other. As a result, a gap significantly wider than the gap during the normal operation (the first gap) is secured between the peripheral surface of the photosensitive drum211and the peripheral surface of the developing roller231(this wider gap is referred to as a second gap).

Mainly with reference toFIGS. 4-8and13, the following describes details of the mechanism for moving the photosensitive drum211and the developing roller231to have the respective peripheral surfaces closer to each other or away from each other.FIG. 4is a perspective view showing the developing unit23along with its surrounding units. InFIG. 4, the photosensitive drum211is illustrated alone, from among components of the drum unit21, in a manner to reflect its relative location.FIG. 5is a perspective view of the support unit30and a switching mechanism40.FIG. 6is a perspective view showing the developing unit23alone.FIGS. 7 and 8each show the image forming apparatus1with the respective units assembled in the main housing10.

As shown inFIG. 4, the image forming apparatus1includes the support unit30, the switching mechanism40, a pair of front and rear coil springs (urging members)50. The support unit30is supported by the main housing10to be freely pivotable about an axis of a pivot shaft A. The pivot shaft A extends in the front-and-rear direction (Y direction). The support unit30places and supports the developing unit23in position.

As shown inFIG. 5, the support unit30includes a base31, a left wall32(first side wall), and a rear wall33(second side wall). The base31is formed of a horizontally extending plate. In detail, the base31is formed of a rectangular plate elongated in the front-and-rear direction (Y direction). As shown inFIG. 4, the developing unit23is mounted on the upper face of the base31. The lower face of the base31faces toward the switching mechanism40.

A right guide section34is disposed to stand vertically upward from a right edge31R of the base31. The right guide section34has an inverted L shape in cross section taken along the right-and-left direction (X direction). In addition, left guide sections35are disposed near a left edge31L of the base31. Each left guide section35is a convex ridge extending in the front-and-rear direction (Y direction). When slid into the support unit30from the front (from the Y2 direction), the developing unit23is guided by the right guide section34and the left guide section35.

As shown inFIG. 5, the left wall32stands vertically upward from the left edge31L (one edge) of the base31. As shown inFIG. 13, the left wall32is a side wall parallel to the developing roller231. The left wall32is higher at its front edge portion32F and rear edge portion32R than at its central portion.

As shown inFIG. 5, a fulcrum member36is provided inside the front edge portion32F. The fulcrum member36is a hollow cylinder that is open toward the front (toward the Y2 direction). As shown inFIG. 13, a pin74is disposed inside the rear edge portion32R to project toward the rear (toward the Y1 direction). The fulcrum member36and the pin74are coaxial. The fulcrum member36and the pin74together constitute the pivot shaft A of the support unit30. As shown inFIGS. 7 and 8, the fulcrum member36is for receiving insertion of a pin member112of the main housing10. In addition, the pin74is for insertion into a pin receiver72(seeFIG. 11) of a drive unit70, which will be described later. By the insertion of the fulcrum member36and the pin74with their associated members, the support unit30is freely pivotable about the axis of the pivot shaft A.

As shown inFIG. 13, a second coupling gear73(a second drive input section) is assembled to the rear edge portion32R of the left wall32. The second coupling gear73is disposed coaxially with the pin74(or with the pivot shaft A). The second coupling gear73includes, for example, gear teeth formed along an edge of a hollow cylinder that is coaxial with the pin74. The second coupling gear73receives a rotational drive force from a first coupling gear71(seeFIG. 11) of the later-described drive unit70.

As shown inFIG. 5, the rear wall33stands vertically upward from a rear edge31b(another edge) of the base31. The rear wall33is a side wall perpendicular to the left wall32. The left edge of the rear wall33is continuous with the rear edge of the left wall32. The rear wall33has a hollow interior331in which a transmission gear37(transmission mechanism) is rotatably held. The transmission gear37receives a rotational drive force from the second coupling gear73(seeFIG. 13). The rear wall33is provided with a first locating hole381and a second locating hole382that are vertically aligned on the front face (in detail, at a location closer to the right edge) of the rear wall33. In addition, a coupling member39is disposed on the rear wall33at a location closer toward the left edge (toward the X2 direction) of the rear wall33. The coupling member39receives a rotational drive force transmitted from the second coupling gear73(seeFIG. 13).

The base31is open at its front edge31F (the edge toward the Y2 direction). As shown inFIGS. 7 and 8, a pair of hooks311(first engaging piece) is disposed below the base31. Each hook311is a plate that extends obliquely downwardly from the base31to form an angle of approximately 30° or so at a location near the right of the base31. The hook311has a sloped portion312. A gap is present between the sloped portion312and the lower face of the base31.

The following describes the configuration of the developing unit23mainly with reference toFIGS. 6 and 7.

As shown inFIG. 6, the developing unit23includes a developing housing60. The developing housing60accommodates the developing roller231, a first stirring screw232, a second stirring screw233, and a toner supplying screw234.

As shown inFIG. 6, the developing housing60is elongated in the front-and-rear direction (Y direction). The developing housing60is formed of a bottom plate601, a front plate602, a rear plate603, a left plate604, and a top plate605. As shown inFIG. 7, the developing housing60has an opening at a location near the right edge (the edge toward the X1 direction) of the developing housing60. The opening opens toward the Z1 direction and extends in the front-and-rear direction (Y direction). In the opening, the developing roller231is exposed halfway around the peripheral surface.

As shown inFIG. 6, the developing roller231is for bearing toner on its peripheral surface. The developing roller231is supported by the developing housing60to be freely rotatable. As shown inFIG. 7, the peripheral surface of the developing roller231is opposed to the peripheral surface of the photosensitive drum211. The toner carried on the developing roller231is supplied to the photosensitive drum211. With the toner supplied to the developing roller231, the electrostatic latent image formed on the peripheral surface of the photosensitive drum211is developed into a toner image.

Each gap roller23D described above (seeFIG. 13) is disposed at a location near the axial edge of the developing roller231. As shown inFIG. 7, the first and second stirring screws232and233convey toner while stirring the toner within the developing housing60. In addition, the first and second stirring screws232and233charge the toner. The toner supplying screw234is for uniformly supplying toner to the second stirring screw233(in greater detail, within the housing space accommodating the second stirring screw233).

As shown inFIG. 6, the top plate605has a toner inlet61at a location near its front edge. The toner inlet61is for introducing toner into the developing housing60. At the time of toner replenishment, toner stored in the toner container24(seeFIG. 4) is supplied to an intermediate hopper241(seeFIG. 4) and then into the developing housing60from the toner inlet61.

The following now describes a configuration of the intermediate hopper241mainly with reference toFIG. 4.

The intermediate hopper241includes a receiving port, a discharge port, and a toner conveyance path. The receiving port receives toner supplied from the toner container24. The discharge port is opposed to the toner inlet61. The discharge port includes a shutter member. The shutter member opens and closes in response to detachment/attachment of the developing housing60(seeFIG. 6) from/to the main housing10. The toner conveyance path connects the receiving port and the discharge port.

In the image forming apparatus1according to the present embodiment, the intermediate hopper241is located between the toner container24and the developing unit23. With such a configuration, the image forming apparatus1allows the developing unit23to be detached alone from the main housing10, i.e., separately from the toner container24.

With reference toFIGS. 6 and 7, the following continues the description of the configuration of the developing unit23. With the developing unit23mounted on the base31of the support unit30, the bottom plate601faces toward the base31as shown inFIG. 7and the rear plate603(seeFIG. 6) faces toward the rear wall33as shown inFIG. 13. As shown inFIG. 6, a gear housing62is disposed to project at a location on the rear plate603near the right edge thereof. The gear housing62accommodates a developing-roller driving gear63(first drive input section).

As shown inFIG. 6, the gear housing62has an opening at a location toward the left (toward the X2 direction). The gear teeth of the developing-roller driving gear63are partly exposed through the opening. As shown inFIG. 13, the developing-roller driving gear63is attached to the rear end of the rotary shaft of the developing roller231. By the rotational drive force supplied to the developing-roller driving gear63, the developing roller231rotates about the axis of the rotary shaft.

The rear plate603has a window portion at a location near its left edge. A coupling socket65is exposed through the window portion. The coupling socket65is directly connected to the rear end of the rotary shaft of the toner supplying screw234(seeFIG. 7). By the rotational drive force supplied to the coupling socket65, the toner supplying screw234(seeFIG. 7) rotates about the axis of the rotary shaft.

A first locating pin641and a second locating pin642are each disposed on the rear plate603to project at a location near the right edge of the rear plate603(the edge toward the X1 direction). The first and second locating pins641and642are at locations aligned in the up-and-down direction. The first locating pin641is located centrally of the gear housing62. The second locating pin642is located near the lower edge of the rear plate603.

As shown inFIG. 7, the bottom plate601is provided with a right guide rib606(seeFIG. 7) along its right edge. The right guide rib606projects toward the right (toward the X1 direction) and extends in the front-to-rear direction (Y direction). As shown inFIG. 6, the bottom plate601is provided with a left guide rib607along its left edge. The left guide rib607projects toward the left (toward the X2 direction) and extends in the front-to-rear direction (Y direction). A blade66is attached to the right edge of the top plate605. The blade66limits the thickness of the toner layer carried on the peripheral surface of the developing roller231.

The following describes the method for attaching the developing unit23to the main housing10(seeFIG. 1), mainly with reference toFIGS. 5-7.

The developing unit23is attached to the main housing10by a user. In detail, the developing unit23is mounted into the support unit30from the front (from the Y2 direction) by sliding the developing unit23on the base31toward the rear (toward the Y1 direction) of the support unit30. In this way, the developing unit23is attached to the main housing10. To attach the developing unit23into the main housing10, it is preferable to fit the right and left guide ribs606and607respectively into the right and left guide sections34and35of the support unit30. By doing so, the right and left guide ribs606and607are respectively guided by the right and left guide sections34and35when the developing unit23slides toward the rear. This enables the developing unit23to stably slide on the base31. Note that the developing unit23is detached from the main housing10through a procedure in reverse of the above-described procedure.

In the attachment of the developing unit23to the main housing10, when the rear plate603of the developing unit23reaches a predetermined location near the rear wall33of the support unit30, the first and second locating pins641and642come to be inserted into the first and second locating holes381and382, respectively. In addition, the coupling socket65is coupled to the coupling member39.

By the insertion of the first and second locating pins641and642respectively into the first and second locating holes381and382, the developing unit23is placed into an appropriate relative location with respect to the support unit30. In this positional relation, the developing-roller driving gear63makes mesh engagement with the transmission gear37. The gear teeth of the transmission gear37are partly exposed from the housing constituting the rear wall33. Part of the exposed gear teeth meshes with the exposed part of the gear teeth of the developing-roller driving gear63described above. In addition, the coupling socket65is coupled with the coupling member39.

Then, the rotational drive force of the second coupling gear73is transmitted to the transmission gear37and the developing-roller driving gear63. This enables the developing roller231to rotate. Similarly, the rotational drive force is transmitted to the coupling member39and the coupling socket65to enable the toner supplying screw234to rotate.

The pair of coil springs50is a member that supplies an urging force to the support unit30. The support unit30is loaded with the developing unit23. With the urging force supplied by the coil springs50, the support unit30can pivot about the axis of the pivot shaft A. The urging force supplied by the coil spring50is to pivot the support unit30in a direction for moving the peripheral surface of the developing roller231toward the peripheral surface of the photosensitive drum211(approaching direction).

The pair of coil springs50is oriented such that each extending direction coincides with the up-and-down direction (Z direction). The upper end portion of each coil spring50is in contact with the lower face of the base31at a location near the right edge of the base31. The bottom end portion of each coil spring50is in contact with a securing frame member (not shown) of the main housing10. The coil springs50upwardly urge the lower face of the base31each at a location near the right edge31R.

The switching mechanism40switches the position of the support unit30supporting the developing unit23. The switching is made between the fitting position (first position) in which the peripheral surface of the developing roller231is located relatively close to the peripheral surface of the photosensitive drum211and a releasing position (second position) in which the peripheral surface of the developing roller231is located relatively away from the peripheral surface of the photosensitive drum211by resisting the urging force of the coil spring50.

The following describes the method in which the switching mechanism40performs the position switching of the support unit30, mainly with reference toFIGS. 7,8, and13.FIG. 7is a cross sectional view showing the support unit30in the fitting position.FIG. 8is a cross sectional view showing the support unit30in the releasing position.

To switch the support unit30into the fitting position, the switching mechanism40supplies no constraining force on the support unit30. Consequently, the urging force of the coil springs50is supplied on the support unit30. Thus, the support unit30pivots about the pivot shaft A (the axis of the fulcrum member36) in the counterclockwise direction indicated by the arrow R11 inFIG. 7. Then, as the support unit30pivots, the developing roller231is pressed in a direction toward the photosensitive drum211as indicated by the arrow R12 inFIG. 7. As a result, each gap roller23D is pressed against the non-image forming region211D of the photosensitive drum211to leave a predetermined gap between the peripheral surface of the developing roller231and the peripheral surface of the photosensitive drum211as shown inFIG. 13. This state where the peripheral surface of the developing roller231is located relatively close to the peripheral surface of the photosensitive drum211is the fitting position. The fitting position is taken when the image forming apparatus1performs image forming processing.

On the other hand, to switch the support unit30into the releasing position, the switching mechanism40supplies a constraining force on the support unit30. In detail, the switching mechanism40supplies a force pressing the hooks311downward against the urging force of the coil springs50. In response, the base31is pressed downward along its right edge (the edge toward the X1 direction). Consequently, the support unit30pivots about the pivot shaft A in the clockwise direction indicated by the arrow R21 inFIG. 8. Then, as the support unit30pivots, the developing roller231is pressed to move in a direction away from the photosensitive drum211as indicated by the arrow R12 inFIG. 8. As a result, a relatively large gap is secured between the peripheral surface of the developing roller231and the peripheral surface of the photosensitive drum211. This state where the peripheral surface of the developing roller231is located relatively away from the peripheral surface of the photosensitive drum211is the releasing position. The releasing position is taken to allow the developing unit23to be pulled forward away from the support unit30(or to be pressed rearward into the support unit30).

The following describes the configuration of the switching mechanism40mainly with reference toFIGS. 9 and 10. The switching mechanism40performs the position switching of the support unit30between the fitting position and the releasing position.FIG. 9is a perspective view showing the switching mechanism40in the state where switching to the fitting position is effected.FIG. 10is a perspective view showing the switching mechanism40in the state where switching to the releasing position is effected.

The switching mechanism40includes a lever member41movable in the front-and-rear direction (Y direction) and two movable plates42each movable in the right-and-left direction (X direction) cooperatively with the front-to-rear (Y direction) movement of the lever member41. The movable plates42are disposed below the lever member41. In detail, the two movable plates42are spaced apart in the front-and-rear direction (Y direction).

The lever member41is a plate elongated in the front-and-rear direction (Y direction). The lever member41includes an operation portion411at the front (toward the Y2 direction) and a transitional portion412continuous from the rear portion (the portion toward the Y1 direction) of the operation portion411.

The operation portion411occupies ⅕ or so of the entire length of the lever member41, starting from the front edge41F in the front-and-rear direction (Y direction). The operation portion411is relatively thick in the up-and-down direction (Z direction). The operation portion411has an operation hole44therethrough for insertion of a user's finger when the user operates the lever member41. InFIGS. 3 and 4, the forwardly (toward the Y2 direction) protruding portion corresponds to the operation portion411.

The transitional portion412is relatively thin in the up-and-down direction (Z direction). The outer edges of the transitional portion412are surrounded by a rib having the same thickness as the operation portion411. Of the two movable plates42, one at the front (toward the Y2 direction) is disposed at a location near the front edge of the transitional portion412. On the other hand, the movable plate42at the rear (toward the Y1 direction) is disposed at a location near the rear edge of the transitional portion412. The transitional portion412has slits43one near the front edge and another near the rear edge thereof. Each slit43extends in a direction oblique to the extending direction of the lever member41.

The following describes the slit43located at the front (toward the Y2 direction). The slit43has a proximal end43A at a location near the front edge and near the right edge of the transitional portion412. The slit43extends from the proximal end43A in a direction obliquely rearward left (toward the X2-Y1 direction) to reach a distal end43B located at a predetermined distance rearward (toward the Y1 direction) from the front edge of the transitional portion412. The distal end43B is at a location near the left edge of the transitional portion412. The slit43at the rear (toward the Y1 direction) is identical in shape to the slit43at the front. The distal end of the slit43at the rear (the portion corresponding to the distal end43B) reaches a location near the rear edge41R of the lever member41(the rear edge of the transitional portion412).

Each movable plate42includes a base plate421, a first guide groove422, a second guide groove423, a fitting pin45, and an engaging pin46(second engaging piece). The base plate421is a flat plate elongated in the right-and-left direction (X direction). The first and second guide grooves422and423each extend through the entire base plate421in the up-and-down direction. The fitting pin45stands vertically on the upper face of the base plate421. The engaging pin46is attached to the base plate421at a location near the right edge of the base plate421.

The first and second guide grooves422and423are each formed at a location centrally of the base plate421in the front-and-rear direction (Y direction). The first and second guide grooves422and423each extend in the right-and-left direction (X direction). The first guide groove422is located closer to the right (toward the X1 direction), whereas the second guide groove423is located closer to the left (toward the X2 direction). The first guide groove422has, for example, a U shape that is open at the right edge (the edge toward the X1 direction) in top view. The second guide groove423has, for example, an elliptical shape in top view.

The main housing10has guide pins (not shown) secured thereto. The guide pins are respectively fitted into the guide grooves422and423. The engagement of the guide pins into the guide grooves422and423prevents each movable plate42from being detached upward (toward Z1 direction) from the main housing10. By being guided by the respective guide pins engaged with the first and second guide grooves422and423, the movable plate42is allowed to move in the right-and-left direction (X direction). The width of the second guide groove423in the right-and-left direction (X direction) determines a movement stroke of the movable plate42in the right-and-left direction (X direction).

The movable plate42at the front (toward the Y2 direction) has an extended portion425extended from a location toward the rear of the base plate421(toward the Y1 direction). The fitting pin45vertically stands on the top face of the extended portion425. The fitting pin45is fitted into the slit43.

As described above, the slit43extends obliquely, rather than straight in the front-and-rear direction (Y direction). The lever member41guided by a guide member (not shown) to move straight along the front-and-rear direction (Y direction). As the lever member41moves in the front-and-rear direction (Y direction), the fitting pin45is guided by the slit43. Consequently, the movable plate42moves in the right-and-left direction (X direction). With the fitting pin45engaged with the slit43, the movement stroke of the lever member41in the front-and-rear direction (Y direction) is limited to the length of the slit43in the front-and-rear direction (Y direction).

The engaging pin46has a cylindrical shape extending in the front-and-rear direction (Y direction). A pair of front and rear retaining portions is provided to upwardly (in the Z1 direction) stand on the right edge of the upper face of the base plate421. The pair of front and rear retaining portions424retains the engaging pin46by holding the respective ends of the engaging pin46. The engaging pins46are engageable with the respective hooks311(first engaging piece) of the support unit30(seeFIGS. 7 and 8).

The following describes the operation of the switching mechanism40mainly with reference toFIGS. 7 to 10.

When the lever member41is pressed to the rearmost location (toward the Y1 direction), the switching mechanism40is placed into the state shown inFIGS. 7 and 9(the state where the lever member41is in the second location). In this state, each fitting pin45is in contact with the proximal end43A of the corresponding slit43. In addition, each movable plate42is located the rightmost (toward the X1 direction).

As shown inFIG. 7, each hook311has the sloped portion312that slopes downwardly toward the right (toward the X1 direction). An opening gap is secured between the tip (lower end) of the hook311and the lower face of the base31. When the lever member41is at the rearmost location (toward the Y1 direction), each engaging pin46is located to the right (toward the X1 direction) of the opening gap. Note that the engaging pin46is located higher than the lower end of the hook311. In the state shown inFIG. 7, the engaging pin46is retracted to a location toward the right (toward the X1 direction), the engagement between the engaging pin46and the hook311of the support unit30is released. When the engagement between the engaging pin46and the hook311is released, the urging force of the coil springs50acts on the support unit30without being restricted. Therefore, the support unit30is urged upward by the coil springs50. As a consequence, the support unit30takes the fitting position.

When the lever member41in the state shown inFIG. 9is pulled forward (in the direction indicated by the arrow R3 inFIG. 10) to bring the front edge41F to the foremost location, the switching mechanism40is placed into the state shown inFIGS. 8 and 10(the state where the lever member41takes the first position). In this state, the fitting pin45is in contact with the distal end43B of the slit43. As the fitting pin45moves from the proximal end43A toward the distal end43B, the movable plate42is guided by the slits43to move toward left (toward the X2 direction) as indicated by the arrow R4 inFIG. 10. When the fitting pin45reaches the distal end43B, the movable plate42comes to be located at the leftmost location (toward the X2 direction).

As shown inFIG. 8, when the lever member41is placed to the foremost location (toward the Y2 direction), the engaging pin46has moved toward the left (X2 direction) to engage with the hook311. In detail, when the movable plate42moves toward the left (toward the X2 direction), the engaging pin46also moves toward the left (toward the X2 direction). As a consequence, the engaging pin46comes to engage the hook311at the lower end of the sloped portion312. Thereafter, as the engaging pin46slides along the sloped portion312toward the left (toward the X2 direction), the support unit30is gradually pressed downward. In this way, the support unit30receives via the hooks311a force pressing the support unit30downward against the urging force of the coil springs50. As a consequence, the support unit30is placed in the releasing position.

The image forming apparatus1further includes the drive unit70. The drive unit70is assembled to the main housing10. The drive unit70generates a drive force for driving the photosensitive drum211, the developing roller231, and the like. The following describes a configuration of the developing unit70mainly with reference toFIG. 11.

The drive unit70includes a gear housing70H and a drive motor (not shown). The gear housing70H accommodates a plurality of gear trains. The drive motor supplies a rotational drive force to each gear train. The gear housing70H is assembled to the front face (toward the Y2 direction) of a side frame18, which is a component of the main housing10. The drive motor is attached to the rear face (toward the Y1 direction) of the side frame18. Note that the gear housing70H functions as a retaining member of a high-voltage board19. On the high-voltage board19, electric components (for example, a power semiconductor) operating at high-voltage are mounted.

The drive unit70has a drive output shaft. The drive output shaft generates a rotational drive force that rotates about its axis. According to the present embodiment, the first coupling gear71is an example of the drive output shaft.

The first coupling gear71includes a hollow cylinder and gear teeth formed along an edge of the hollow cylinder. The first coupling gear71is coupled with the second coupling gear73(seeFIG. 13). The first coupling gear71is provided with the pin receiver that is disposed on its axis. The pin receiver72is for insertion of the pin74(seeFIG. 13). The pin74is coaxial with the second coupling gear73. The first coupling gear71generates a rotational drive force for counterclockwise rotation as indicated by the arrow R5 inFIG. 11.

The following describes the assembled state of the drive unit70with the developing unit23and the support unit30, mainly with reference toFIGS. 11-13.FIG. 12is a perspective view showing the assembled state of the drive unit70with the developing unit23and the support unit30.

For example, the support unit30on which the developing unit23is mounted is assembled to the drive unit70. In the state where the support unit30is assembled to the drive unit70(the state shown inFIG. 12), the rear wall33is in contact with the gear housing70H (seeFIG. 11). The second coupling gear73is exposed from the rear wall33. This allows the first coupling gear71to be coupled with the second coupling gear73. In addition, the pin74is inserted into the pin receiver72. In the state shown inFIG. 12, the rotational drive force of the first coupling gear71can be transmitted to the second coupling gear73. In the state shown inFIG. 12, in addition, the support unit30is supported axially by the pin receiver72(and by the pin member112inserted into the fulcrum member36).

When the drive motor described above is driven in the state shown inFIG. 12, the first coupling gear71rotates in the direction indicated by the arrow R5 shown inFIG. 11. In addition, the second coupling gear73rotates in the direction indicated by the arrow R6 shown inFIG. 13. In addition, as the second coupling gear73rotates, the transmission gear37and the developing roller231rotate.

In the image forming apparatus1according to the present embodiment, the rotation direction R5 of the first coupling gear71and the rotation direction R6 of the second coupling gear73are both in the direction for moving the developing roller231toward the photosensitive drum211. The rotation directions R5 and R6 each coincide with the pivoting direction for moving the peripheral surface of the developing roller231toward the peripheral surface of the photosensitive drum (approaching direction), out of the two possible pivot directions about the axis of the pivot shaft A. The fulcrum member36and the pin74of the support unit30together constituting the pivot shaft A are both coaxial with the first and second coupling gears71and73. When each of the first and second coupling gears71and73rotates, a driving force acts on the support unit30for pivoting the support unit30about the axis of the pivot shaft A in the corresponding rotation direction.

In the image forming apparatus1according to the present embodiment, the developing unit23is supported by the support unit30to be freely pivotable about the pivot shaft A. The support unit30is urged by the coil springs50in the approaching direction for moving the peripheral surface of the developing roller231toward the peripheral surface of the photosensitive drum211. The coil springs50generate an urging force urging the support unit30to pivot. In detail, in the state mounted on the top face of the horizontal base31, the developing unit23is urged to pivot about the axis of the pivot shaft A by the urging force of the coil springs50. The pivot shaft A is disposed on the left wall32.

In addition, the first coupling gear71(the drive output shaft of the drive unit70) is set to generate a rotational drive force in the direction for pivoting the support unit30into the approaching direction. That is, the support unit30is pivoted by the urging force of the coil springs50and also by the rotational drive force of the first coupling gear71(the drive output shaft of the drive unit70). In the image forming apparatus1according to the present embodiment, the force required to pivot the support unit30about the axis of the pivot shaft A is supplied partly by the urging force of the coil springs50and partly by the driving force generated by the rotation of the first coupling gear71.

Since the rotational drive force generated by the first coupling gear71(the output shaft of the drive unit70) contributes the pivoting of the support unit30, the urging force of the coil springs50is allowed to be smaller. In detail, when the image forming apparatus1is in the operating state (the state where the developing roller231is rotated), the driving force generated by rotation of the first coupling gear71serves as an additional urging force. Therefore, the force pressing the gap rollers23D against the non-image forming regions211D of the photosensitive drum211is unlikely to fall short even if the urging force of the coil springs50is small.

Reducing the urging force of the coil springs50improves the operability of the switching mechanism40. In detail, the switching mechanism40switches the support unit30from the fitting position to the releasing position by resisting the urging force of the coil springs50. Therefore, the force required for the user to apply when making an operation for effecting the switching can be made smaller.

As described above, the switching mechanism40according to the present embodiment is simple in configuration. The switching mechanism40according to the present embodiment can perform the position switching of the support unit30between the fitting position and the releasing position, simply by switching the location of the lever member41between the front and the rear. The switching mechanism40according to the present embodiment can reduce the urging force of the coil springs50acting on the support unit30when the lever member41is pulled toward the front (moving the lever member41from the second location to the first location). As a result, the operability of the lever member41improves.

As has been described above, the image forming apparatus1according to the present embodiment is provided with a mechanism for moving the developing roller231closer to and away from the photosensitive drum211. This can improve the user operability for causing the distal and proximal movements.

The embodiment described above is one example and may be modified. For example, the embodiment described above employs the first coupling gear71as the drive output shaft and the second coupling gear73as the second drive input section. In addition, the first coupling gear71is provided with the pin receiver72that is disposed on its axis, and the second coupling gear73is provided with the pin74that is disposed on its axis. Such configuration is simple and still allows the drive force to be transmitted from the drive output shaft to the second drive input section and also allows the pivot shaft and the second drive input section to be coaxial. However, the above configuration is without limitation and may be replaced by another configuration. For example, spur gears may be used instead.