Image forming apparatus having a driving force transmission rotating body which transmits a driving force to a driving force receiving portion of a driven member

Provided is a technique for suppressing the occurrence of density non-uniformities in an image formed on a sheet. An image forming apparatus, which forms an image on a recording material by transmitting driving force to a cartridge, includes: a frame having a positioning portion which positions the cartridge by contacting the attached cartridge; a driving force transmission rotating body which transmits driving force by engaging with a driving force receiving portion of the driven unit; and a circumferential surface which is provided in one portion of the frame and rotatably supports the driving force transmission rotating body.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an image forming apparatus provided with a drive transmission mechanism for transmitting drive to a driven unit, such as a cartridge.

Description of the Related Art

Recent years have seen a requirement for image forming apparatuses, such as copying machines, laser beam printers and inkjet printers, to be capable of forming images of high definition. Therefore, the resolution of an image formed on a sheet is improved by improvement of the toner and/or intermediate transfer belt, etc. Here, there are cases where rotational non-uniformities occur in rotating bodies, such as the photosensitive drum and developing roller.

A rotational non-uniformity means a variation in the angular velocity of rotation of the rotating body. There are cases where density non-uniformities occur in the image formed on a sheet, due to the occurrence of rotational non-uniformities in the photosensitive drum, developing roller, and the like. A density non-uniformity means that the density of the image formed on the sheet is not constant.

When a very slight rotational non-uniformity has occurred in the photosensitive drum, or the like, the density non-uniformity caused in the image is often so small as to be imperceptible. However, with the recent increase in image resolution, even if a very small rotational non-uniformity has occurred in the photosensitive drum, or the like, this may be perceptible as a density non-uniformity in the image. The causes of rotational non-uniformities are considered to be eccentricity in the rotating bodies, such as the photosensitive drum, the developing roller and the gears.

Eccentricity occurs in a rotating body due to divergence or inclination, etc. of the rotational center axis of the rotating body, which means that driving force is not transmitted accurately from the drive source to the rotating body and variations may occur in the angular velocity of rotation of the rotating body. In other words, it is necessary to reduce rotational non-uniformities in order to suppress density non-uniformities occurring in the image.

In order to resolve this problem, in Japanese Patent No. 3211780, bearings which support a rotary shaft of a gear that transmits drive to a photosensitive drum, or the like, and a frame which supports the bearings, are formed integrally. More specifically, burring is provided on a metal frame, and by using the burring as the bearings, the rotational accuracy of the gear is improved. If the frame and bearings are formed as separate members, then the rotational accuracy of the gear deteriorates due to error in the positioning of the bearings with respect to the frame.

However, by unifying the frame and bearings in an integrated body, it is possible to improve the rotational accuracy of the gear, accordingly, without the occurrence of any positioning errors of the bearings with respect to the frame. Here, in Japanese Patent No. 3211780, a process cartridge having a rotating body, such as a photosensitive drum, is positioned in a frame that is separate from the frame in which the burring is formed. The frame in which the burring is formed, and the frame in which the process cartridge is positioned are then coupled by screws, or the like.

Furthermore, conventionally, a drive transmission mechanism100such as that shown inFIG. 7is known. The drive transmission mechanism100has a frame101, a bearing102, a drive transmission member106and a drive coupling member107. Drive which is transmitted to the drive transmission member106from drive means (not illustrated) is transmitted to the drive coupling member107, and is transmitted to a supply roller115from the drive transmission member106via the drive receiving member111. The drive coupling member107which transmits the drive to a driven unit110is supported rotatably by a bearing102attached on the frame101.

However, in Japanese Patent No. 3211780, a process cartridge having a rotating body, such as a photosensitive drum, is positioned in a frame that is separate from the frame in which the burring is formed. Therefore, the rotational accuracy of the photosensitive drum, and the like, provided in the process cartridge, declines to the extent that error occurs in the positioning of the frame in which the process cartridge is supported and the frame in which the burring is formed. Consequently, there is a risk of density non-uniformities in the image formed on the sheet.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a technique for suppressing the occurrence of density non-uniformities in an image formed on a sheet.

An object of the present invention is to provide an image forming apparatus in which a cartridge is attached and which forms an image on a recording material by transmitting driving force to the cartridge, the image forming apparatus comprising:

a frame having a positioning portion which positions the cartridge by contacting the cartridge;

a driving force transmission rotating body which transmits driving force by engaging with a driving force receiving portion of the cartridge; and

a circumferential surface which is provided on the frame and rotatably supports the driving force transmission rotating body.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention are described below with reference to the drawings. The dimensions, materials, shapes and relative positions, and the like, of the constituent parts described in these embodiments should be changed appropriately depending on the composition and various conditions of the apparatus to which the invention is applied, and it is not intended to limit the scope of the invention to the description of the embodiments given below.

<Configuration of Image Forming Apparatus>

FIG. 1is a schematic cross-sectional diagram of an image forming apparatus1relating to the present embodiment. Firstly, the general configuration of the image forming apparatus1will be described with reference toFIG. 1. The image forming apparatus1is a color laser printer, and a cassette11loaded with recording paper is provided in the lower portion of the image forming apparatus1so as to be insertable in an apparatus main body. The recording paper loaded in the cassette11is separated and paid out, one sheet at a time, by a pick-up roller12and paper supply roller13, and is conveyed by a conveyance roller pair14and a conveyance roller pair15towards a secondary transfer roller25. Furthermore, the conveyance roller pair15has a registration function for synchronizing the toner image formed on the intermediate transfer belt23, and the recording material.

Moreover, the image forming apparatus1has four process cartridges60(60Y,60M,60C,60K) (driven units) which can be attached in and removed from the apparatus main body of the image forming apparatus1. InFIG. 1, the process cartridges60are, arranged in order from the left-hand side, a process cartridge60Y (yellow), a process cartridge60M (magenta), a process cartridge60C (cyan) and a process cartridge60K (black). Here, in the present embodiment, the configuration of the process cartridges60Y to60K is the same, apart from the color of the toner held therein, and therefore unless specifically necessary below, the suffixes Y, M, C and K are omitted below.

The scanner21forms an electrostatic latent image on a photosensitive drum22(22Y to22K) by irradiating the photosensitive drum22, which has been charged by a charging roller, with a laser. Furthermore, the toner held inside the process cartridge60is supplied to a developing roller66(developer carrying member) by a supply roller65(65Y to65K) which is a supply member (seeFIG. 2AandFIG. 2B). The developing roller66carries toner. A developing bias is applied between the developing roller66and the photosensitive drum22, and the toner carried on the developing roller66is supplied to the photosensitive drum22, thereby developing the electrostatic latent image on the photosensitive drum22.

The toner images formed on the photosensitive drums22are primarily transferred onto the intermediate transfer belt23by the application of a bias to the primary transfer rollers24(24Y to24K). The toner images are then conveyed to a secondary transfer position, in a state where the toner images of four colors have been superimposed on each other on the intermediate transfer belt23. Furthermore, the toner image of four colors on the intermediate transfer belt23is transferred secondarily onto the recording material by a secondary transfer roller25, at the secondary transfer position. The toner image transferred secondarily onto the recording material is fixed to the recording material by being heated and pressurized by the fixing roller31.

The recording material on which the toner image has been fixed is then discharged to a paper discharge tray34situated outside the image forming apparatus1, by a discharge roller32. Furthermore, when forming an image on both surfaces of the recording material, the recording material is switched back by a reversal roller33, and is conveyed again to the conveyance roller pair15by the conveyance roller pair41and the conveyance roller pair42. An image is then formed on the rear surface of the recording material, by a similar procedure to that for forming an image on the front surface of the recording material. The recording material having an image formed on the rear surface thereof is then discharged to a paper discharge tray34.

<Configuration of Process Cartridge>

Next, the configuration of the process cartridge60will be described with reference toFIG. 2AandFIG. 2B.FIG. 2AandFIG. 2Bare schematic cross-sectional drawings of a process cartridge60viewed in the direction of the axis of rotation of the photosensitive drum22. As shown inFIG. 2A, the process cartridge60has a photosensitive body unit63having a photosensitive drum22, and a developing unit64having a developing roller66and a supply roller65. The image forming apparatus1is provided with a frame51, which is one portion of the framework of the apparatus. The frame51is a plate-shaped metal member (metal plate) which extends in the vertical direction and in the direction of arrangement of the plurality of photosensitive drums22. The photosensitive drum22is positioned with respect to the frame51by being pressed by pressing means (not illustrated) in the direction of arrow A towards a positioning portion53of the frame51, via a bearing69(bearing member) for the photosensitive drum22. The photosensitive body unit63is registered in position by fitting together of a rotation stopping portion67, which is a fitting portion, and a fit receiving portion (not illustrated) which is provided in the frame51. Furthermore, the developing unit64is supported rotatably about a swinging shaft68, with respect to the photosensitive body unit63.

The developing roller66is impelled by impelling means (not illustrated) in a direction towards the photosensitive drum22. When developing the electrostatic latent image on the photosensitive drum22, the developing roller66makes contact with the photosensitive drum22, as shown inFIG. 2A. On the other hand, when not developing the electrostatic latent image on the photosensitive drum22, as shown inFIG. 2B, the photosensitive drum22and the developing roller66are set to a separated state, due to the developing unit64being pressed in the X direction by a separating member91.

FIG. 3is a cross-sectional diagram of the developing unit64and the drive transmission mechanism90of the image forming apparatus1, as viewed in a direction perpendicular to the direction of the axis of rotation of the supply roller65. In the developing unit64, as shown inFIG. 3, the drive transmitted to the drive receiving member (driving force receiving portion)61can be transmitted to the supply roller65via a joint62. The driving force transmitted to the supply roller65is transferred to the developing roller66via a gear (not illustrated).

When an electrostatic latent image on the photosensitive drum22is not being developed in the process cartridge60as described above, then the photosensitive drum22and the developing roller66are separated from each other. It will now be explained why it is necessary to separate the photosensitive drum22and the developing roller66. If a toner image is formed on the photosensitive drum22, firstly, the photosensitive drum22rotates in a state where the photosensitive drum22and the developing roller66are separated. The photosensitive drum22is irradiated with a laser from the scanner21, thereby forming an electrostatic latent image on the photosensitive drum22.

Next, the developing roller66is made to contact the photosensitive drum22, in a state where the developing roller66and the supply roller65are rotating. By applying a bias to the developing roller66in a state where the photosensitive drum22and the developing roller66are in contact with each other, the electrostatic latent image on the photosensitive drum22is developed. Here, the photosensitive drum22and the developing roller66rotate at different speeds of rotation. Therefore, when the rotating photosensitive drum22and the rotating developing roller66make contact, rubbing occurs between the photosensitive drum22and the developing roller66, leading to abrasion and wearing of the photosensitive drum22and the developing roller66. This abrasion and wearing shorten the life of the photosensitive drum22and the developing roller66. Consequently, by reducing the rubbing time between the photosensitive drum22and the developing roller66, it is possible to lengthen the life of the photosensitive drum22and the developing roller66. Therefore, the photosensitive drum22and the developing roller66are separated when not developing an electrostatic latent image.

However, since the photosensitive drum22and the developing roller66may be in a separated state, then there may be cases where drive is transmitted to the developing roller66in this separated state. When the photosensitive drum22and the developing roller66are in a separated state, the positions of the rotational center axis72A of the drive coupling member (driving force transmission rotating body)72(seeFIG. 3) and the rotational center axis of the supply roller65deviate while maintaining a parallel relationship. The joint62is provided in the process cartridge60in such a manner that drive is transmitted to the supply roller65even in this state. In the present embodiment, an Oldham coupling is used as the joint62, but the joint62may also be a disk coupling, or the like. Here, as shown inFIG. 3, the process cartridge60has a drive receiving member61and a joint62. The drive receiving member61has a driving force receiving portion61a, and by engagement of the driving force receiving portion61aand the drive coupling portion72aof the drive coupling member72, drive is transmitted from the drive coupling member72to the drive receiving member61. The joint62can transmit drive from the drive coupling member72to the supply roller65, even if there is deviation between the rotational center axis72A of the drive coupling member72and the rotational center axis of the supply roller65.

<Configuration for Transmitting Drive to Process Cartridge>

Next, the mechanism for transmitting drive to the process cartridge60will be described with reference toFIG. 3toFIG. 5.FIG. 3is a cross-sectional drawing illustrating a mechanism for transmitting driving force to the process cartridge60according to a first embodiment of the invention.FIG. 4is a cross-sectional diagram showing the state of a drive input rotating body70in a case where the process cartridge60has been removed.FIG. 5is a diagram showing a state where the photosensitive drum22has been positioned on the frame51.

As shown inFIG. 3, the drive transmission mechanism90includes the frame51, a cylindrical projecting portion52which is provided to project in the main body portion of the frame51, and the drive input rotating body70which is supported rotatably on the projecting portion52. Furthermore, the drive input rotating body70includes the drive transmission member71and the drive coupling member72. The drive transmission member71has a drive transmission portion71a, which is a gear tooth surface, and the drive coupling member72has a drive coupling portion72afor transmitting drive to the process cartridge60.

When drive means (not illustrated) is driven, driving force is transmitted to the drive transmission member71due to a gear (not illustrated) engaging with the drive transmission portion71a. Due to the engagement of the drive transmission member71and the drive coupling member72, the driving force transmitted to the drive transmission member71is transmitted to the drive coupling member72. A groove (not illustrated) is provided in the drive transmission member71, and a rib (not illustrated) is provided in the drive coupling member72. The rib provided in the drive coupling member72engages with the groove provided in the drive transmission member71, whereby the driving force is transmitted from the drive transmission member71to the drive coupling member72.

The driving force transmitted to the drive coupling member72is transmitted to the drive receiving member61. A groove-shaped drive coupling portion72ais provided in the drive coupling member72, and a driving force receiving portion61a, which is a rib, is provided in the drive receiving member61. Due to the drive coupling portion72aprovided on the drive coupling member72engaging with the driving force receiving portion61aprovided on the drive receiving member61, driving force is transmitted from the drive coupling member72to the drive receiving member61. Furthermore, similarly, a rib (not illustrated) is provided on the drive receiving member61and a groove (not illustrated) is provided in the joint62. The rib provided on the drive receiving member61engages with the groove provided in the joint62, whereby the driving force is transmitted from the drive receiving member61to the drive joint62.

In this way, in the present embodiment, the drive input rotating body70includes the drive transmission member71and the drive coupling member72. Here, the drive transmission member71is positioned by a shaft75, and the drive coupling member72is positioned by the projecting portion52. Supposing that the drive transmission member71and the drive coupling member72are formed by a single member as the drive input rotating body70, then if there is deviation in the position where the axis of rotation of the drive input rotating body70is supported, the drive input rotating body70is rotated in an inclined state.

When the drive input rotating body70is rotated in an inclined fashion, rotational non-uniformities occur in the supply roller65, since the drive ceases to be transmitted satisfactorily from the drive input rotating body70to the drive receiving member61, and there is a risk of deterioration in the image quality. However, in the present embodiment, the drive input rotating body70is configured by mutual engagement of separate members, namely, the drive transmission member71and the drive coupling member72. Due to the occurrence of play between the drive transmission member71and the drive coupling member72, it is possible to transmit drive from the drive transmission member71and the drive coupling member72, without inclination of the drive transmission member71. Consequently, it is possible to suppress inclination of the tooth surface of the drive transmission portion71a(gear) in the drive transmission member71, and therefore it is possible to suppress rotational non-uniformities occurring due to intermeshing of the tooth surfaces of the gears.

Here, in the first embodiment, a cylindrical projecting portion52is formed in the frame51. The cylindrical projecting portion52supports the drive coupling member72in a rotatable fashion. Furthermore, the central axis52A of the cylindrical projecting portion52coincides with the rotational center axis72A of the drive coupling member72. The circumferential surface52sof the cylindrical projecting portion52supports the drive coupling member72rotatably about the rotational center axis72A. As shown inFIG. 3, the circumferential surface52sis the inner circumferential surface of the cylindrical projecting portion52. In the present embodiment, the projecting portion52is formed on the frame51by which the photosensitive drum22is positioned in the process cartridge60. Furthermore, the frame51and the projecting portion52are made from a metallic material. The material of the frame51is not necessarily limited to this. The frame51and the projecting portion52may be, for example, made from a resin material which has excellent strength and heat resistance. For example, the frame51may be made from a polymer alloy material including a polycarbonate resin and an acrylonitrile butadiene styrene (ABS) resin.

Furthermore, in the present embodiment, as described above, the frame51is made from a metallic material. Consequently, it is possible to improve the heat conductivity of the frame51, compared to a case where the frame51is made from a resin material. In the present embodiment, the photosensitive drum22and the developing roller66are in a separated state in the process cartridge60, except when forming an image. In this separated state, drive is transmitted from the drive coupling member72to the supply roller65, in a state where there is great deviation between the central axes of rotation of the drive coupling member72and the supply roller65. Consequently, a load is applied to the drive coupling member72in a direction perpendicular to the direction of the rotational center axis of the drive coupling member72.

Furthermore, in recent years, the speed of image formation in an image forming apparatus1has been increasing. In accordance with this, the speed of rotation of the drive coupling member72has become dramatically faster. When the load on the drive coupling member72and the speed of rotation of the drive coupling member72are high, abrasion and wear occurs in the drive coupling member72due to increase in the temperature of the rubbing portions of the drive coupling member72and the projecting portion52, as a result of the heat of friction.

Furthermore, if the frame51is made from resin, there is a risk of burning of the frame51if the temperature in the rubbing portions of the drive coupling member72and the projecting portion52becomes higher than the thermal resistance temperature of the resin. Consequently, by forming a frame51from a material having a high thermal conductivity, such as a metal, the heat radiating properties are raised in the rubbing portions of the drive coupling member72and the projecting portion52, and the occurrence of abrasion or wear, or burning, etc. in the frame51, can be suppressed. Furthermore, although a large load is applied to the projecting portion52, by using a metallic plate material which has greater rigidity than a resin material as the material of the frame51, it is possible to suppress the occurrence of elastic deformation and/or creep in the projecting portion52, and to position the drive coupling member72accurately.

Furthermore, in the present embodiment, the cylindrical projecting portion52is formed by a burring process. The drive transmission member71is supported rotatably by the shaft75, and furthermore, the drive coupling member72is supported movably in the direction of the rotational center axis of the drive coupling member72. The drive coupling member72is disposed on the side nearer to the process cartridge60than the drive transmission member71(the side of the driven unit). Furthermore, an impelling member76is attached on the drive transmission member71and the drive coupling member72, thereby impelling the drive coupling member72towards the process cartridge60.

Next, the positional relationship between the drive coupling member72and the projecting portion52in a state where the process cartridge60has been removed from the image forming apparatus1will be described.FIG. 4is a cross-sectional drawing showing the vicinity of the drive coupling member72, when the process cartridge has been removed, as viewed in a direction perpendicular to the rotational center axis72A. The process cartridge60is removed from the image forming apparatus1in a direction B1parallel to the rotational center axis72A, away from the drive transmission member71with respect to the frame51.

Here, the drive coupling member72can be moved with respect to the projecting portion52, in the direction of the rotational center axis72A of the drive coupling member72. InFIG. 4, the drive coupling member72can be moved in the direction of B1and the direction of B2which is opposite to B1. When the process cartridge60and the drive coupling member72are in an engaged state, then as shown inFIG. 3, the drive coupling member72moves in the direction of B1, and thereby moves to the side where the drive receiving member61of the process cartridge60is disposed. In a state where the drive coupling member72has been moved to the side where the drive receiving member61of the process cartridge60is disposed, the drive coupling member72and the drive receiving member61can be engaged with each other. Due to the drive coupling member72moving in the direction B1when the process cartridge60has been attached on the image forming apparatus1, the drive coupling member72moves towards the process cartridge60, and the driving force receiving portion61aand the drive coupling portion72aengage with each other.

Furthermore, as shown inFIG. 4, the drive coupling member72can also be moved in a direction B2which is opposite to the side where the process cartridge60is disposed. When the process cartridge60is removed from the image forming apparatus1, as shown inFIG. 4, the drive coupling member72moves in the direction B2, moves towards the drive transmission member71, and abuts against the shaft75. In the present embodiment, even if the drive coupling member72has moved to the side of the drive transmission member71, as shown inFIG. 4, the drive coupling member72still projects out to the side where the drive receiving member61of the process cartridge60is disposed (the downstream side in direction B1), beyond the front end of the projecting portion52, in the direction of the rotational center axis72A. Here, the end portion of the drive coupling member72on the side where the drive receiving member61of the process cartridge60is disposed, in the direction of the rotational center axis72A of the drive coupling member72, is called end portion72B. In the present embodiment, in the direction of the rotational center axis72A of the drive coupling member72, the end portion72B is positioned closer to the side where the drive receiving member61of the process cartridge60is disposed (the downstream side in direction B1), than the front end52B of the projecting portion52in the direction of the central axis52A of the projecting portion52is positioned.

In the present embodiment, when the process cartridge60is removed from the image forming apparatus1, a user may directly touch the drive coupling member72or the cylindrical projecting portion52, etc. Therefore, it is desirable if the frame51is made from a hard material, such as a metallic material, thereby making the user less liable to touch the edges of the front end52B of the cylindrical projecting portion52.

Furthermore, the drive coupling member72can be moved between a transmission position, which is a position for when transmitting drive by engaging with the drive receiving member61, and a retracted position, which is a position withdrawn (moved) in the B2direction (a direction away from the drive receiving member61), from the transmission position. Furthermore, at least the surface of the drive coupling member72is made from a resin material. However, as shown inFIG. 4, even in a state where the drive coupling member72is situated in the retracted position, the drive coupling member72projects towards the drive receiving member61in the process cartridge60, with respect to the front end52B of the projecting portion52, in the direction of the rotational center axis72A. Consequently, it is possible to make the user less liable to touch the edges of the front end52B of the projecting portion52.

Next, the positional relationship between the components that constitute the process cartridge60, and the frame51, will be described.FIG. 5is a diagram showing a state where the photosensitive drum22has been positioned on the frame51, and the developing roller66has been placed in contact with the photosensitive drum22. As described above, the photosensitive drum22is positioned with respect to the frame51by abutting against the positioning portion53in the frame51via the bearing69for the photosensitive drum22. A cutaway region (cutaway hole)54which is larger than the bearing69for the photosensitive drum22is formed in the frame51, which is made of plate metal. The cutaway portion54is a portion which is cut out from the frame51. The edge of the cutaway portion54forms a positioning portion53. In other words, in the present embodiment, the photosensitive drum22in the process cartridge60is positioned on the frame51, and the projecting portion52is formed integrally with a portion of the frame51. The circumferential surface52sof the projecting portion52indicated by the dotted line inFIG. 5is a circumferential surface which is coaxial with the supply roller65.

In this way, in the present embodiment, the process cartridge60is positioned by the positioning portion53in the frame51, and the drive coupling member72is supported rotatably by the projecting portion52in the frame51. By supporting the drive coupling member72on the frame51which positions the process cartridge60, without any other intervening components, it is possible to improve the positioning accuracy of the drive coupling member72with respect to the process cartridge60.

Consequently, it is possible to suppress deviation between the rotational center axis of the drive receiving member61in the process cartridge60and the rotational center axis72A of the drive coupling member72, and rotational non-uniformity in the rotating body that is used in the process cartridge60can be suppressed. Furthermore, by supporting the drive coupling member72with the frame51, without an intervening bearing, then it is possible to reduce the number of components used in the image forming apparatus1and the costs can be lowered.

Since rotational non-uniformity of the rotating body used in the process cartridge60can be suppressed, it is possible to effectively suppress density non-uniformity in the image formed on the recording medium. In the process cartridge60, density non-uniformities are liable to occur in the image, if rotational non-uniformity occurs in the rotating body used when forming the electrostatic latent image on the photosensitive drum22, when developing the electrostatic latent image, or when transferring the developer image. Furthermore, in general, the drive transmission mechanism which transmits drive to the process cartridge60and/or intermediate transfer belt23, and the like, has a greater effect on the density non-uniformity of the image, than the mechanisms used in the paper supply device which supplies the recording material, or the fixing device which fixes the toner image on the recording medium, and the like. However, in the present embodiment, since the rotational non-uniformity can be suppressed in the drive transmission mechanism90which transmits drive to the process cartridge60, then it is possible to effectively suppress density non-uniformities occurring the image.

Furthermore, as described above, in the mechanism for transmitting drive to the process cartridge60, there is a risk of density non-uniformities occurring in the image, even if only a slight rotational non-uniformity occurs. Consequently, it is desirable to be able to transmit drive to the process cartridge60by using the minimum necessary members. For example, in the developing unit64, by transmitting drive to the developing roller66by a drive transmission member71which is supported on the projecting portion52, it is thought that the number of components used in the process cartridge60can be reduced.

In this case, as shown inFIG. 5, a cutaway portion54is formed in the frame51and constitutes a positioning portion53by which the bearing69supporting the rotational shaft of the photosensitive drum22is positioned. When the drive coupling member72is disposed on the rotational center axis of the developing roller66, the cutaway portion54and the projecting portion52overlap with each other in the frame51, and therefore it is not possible to form a cylindrical projecting portion52in the frame51. In the present embodiment, the drive coupling member72transmits drive to the supply roller65which is disposed at a position sufficiently distanced from the cutaway portion54. Therefore, it is possible to support the drive coupling member72rotatably by the projecting portion52.

As described above, in the first embodiment, the drive transmission mechanism has a frame including a positioning portion which positions the driven unit. The driving force transmission rotating body is supported rotatably by the circumferential surface provided in one portion of the frame. Consequently, it is possible to position the drive transmission mechanism accurately with respect to the driven unit. By suppressing rotational non-uniformity of the rotating bodies used in the driven unit, density non-uniformity in the image formed on the recording material is suppressed.

Furthermore, in the present embodiment, the end portion of the driving force transmission rotating body on the side of the driving force receiving portion is positioned further towards the driving force receiving portion than the front end of the projecting portion on the side of the driving force receiving portion, in the direction of the rotational center axis of the driving force transmission rotating body. Consequently, even if the driven unit is removed from the image forming apparatus, it is still possible to prevent the user from directly contacting the projecting portion, and therefore injury to the user due to touching the projecting portion can be suppressed.

Furthermore, in the present embodiment, the frame is made from a metallic material. Since metal has a high thermal conductivity, then even if heat of friction occurs between the driving force transmission rotating body and the projecting portion, it is possible to radiate the heat of friction by means of the metal frame.

In the present embodiment, the circumferential surface52sof the projecting portion was a cylindrical surface which is circular in the whole of the circumferential direction, but it is also possible to adopt a configuration in which the circumferential surface52scentered on the rotational center axis72A is formed only in a portion of the circumferential direction, such that the circumferential surface52s can rotatably support the drive coupling member72.

Next, a second embodiment will be described with reference toFIG. 6. In the second embodiment, the shape of the projecting portion of the frame differs from the first embodiment. In the second embodiment, the portions which have the same functions as the first embodiment are labelled with the same reference numerals and description thereof is omitted here. In the present embodiment, in the drive transmission mechanism85, a constricted portion83formed bya constricting process is provided on the frame81which is made from plate metal, and a cylindrical projecting portion82is formed in the vicinity of the center of the constricted portion83. A circular circumferential surface82swhich is centered on a central axis82A coinciding with the rotational center axis72A is formed on the projecting portion82, and the circular circumferential surface82srotatably supports the drive coupling member72.

The constricted portion83is formed in a concave shape on the side where the process cartridge60is not disposed, and is formed in a convex shape on the side where the process cartridge60is disposed. In the present embodiment, the front end82B of the projecting portion82in the direction of the central axis82A of the cylindrical projecting portion82projects in the opposite direction from the side where the process cartridge60is disposed. The cylindrical projecting portion82supports the drive coupling member72in a rotatable fashion, similarly to the first embodiment.

As described above, in the second embodiment, it is possible to produce a similar beneficial effect to the first embodiment. Furthermore, in the second embodiment, the front end of the projecting portion is disposed at an end extending from the side where the driving force receiving portion is disposed, towards an opposite side to the side where the driving force receiving portion is disposed. Consequently, even ina state where the driven unit has been removed from the image forming apparatus, it is possible to prevent injury to the user due to touching the front end of the projecting portion.

In each of the embodiments, the cylindrical projecting portion does not necessarily have to be formed by a burring process. The cylindrical projecting portion may also be formed by a plasticizing process or extrusion process, or the like. There are no limitations on the configuration of the projecting part, provided that the projecting part is configured integrally with the frame, and is also capable of rotatably holding the driving force transmission rotating body.

Furthermore, in the present embodiment, the frame does not necessarily have to be made from metal. There are no limitations in particular on the material of the frame, provided that the material has high thermal conductivity and high rigidity.

In the respective embodiments, the driving force transmission rotating body which is supported rotatably on the projecting portion does not necessarily have to transmit drive to the process cartridge. For example, the driving force transmission rotating body supported rotatably by the projecting portion may also transmit drive to a driven unit, such as an intermediate transfer belt or fixing device. There are no limitations on the configuration of the driving force transmission rotating body, provided that the rotating body is capable of transmitting drive to the units to which drive is transmitted.

This application claims the benefit of Japanese Patent Application No. 2015-121163, filed Jun. 16, 2015, which is hereby incorporated by reference herein in its entirety.