Patent Publication Number: US-9851692-B2

Title: 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

Description:
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 mechanism  100  such as that shown in  FIG. 7  is known. The drive transmission mechanism  100  has a frame  101 , a bearing  102 , a drive transmission member  106  and a drive coupling member  107 . Drive which is transmitted to the drive transmission member  106  from drive means (not illustrated) is transmitted to the drive coupling member  107 , and is transmitted to a supply roller  115  from the drive transmission member  106  via the drive receiving member  111 . The drive coupling member  107  which transmits the drive to a driven unit  110  is supported rotatably by a bearing  102  attached on the frame  101 . 
     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. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional diagram of an image forming apparatus relating to a first embodiment; 
         FIG. 2A  is a schematic cross-sectional diagram of a process cartridge according to a first embodiment, and  FIG. 2B  is a schematic cross-sectional diagram of a process cartridge according to the first embodiment; 
         FIG. 3  is a cross-sectional drawing illustrating a mechanism for transmitting driving force to the process cartridge according to the first embodiment; 
         FIG. 4  is a cross-sectional diagram showing the state of a rotating body in a case where the process cartridge has been removed; 
         FIG. 5  is a diagram showing a state where an image bearing member has been positioned on the frame; 
         FIG. 6  is a cross-sectional drawing illustrating a mechanism for transmitting driving force to the process cartridge according to a second embodiment; and 
         FIG. 7  is a cross-sectional drawing illustrating a mechanism for transmitting driving force to the process cartridge according to the prior art. 
     
    
    
     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. 
     (First Embodiment) 
     &lt;Configuration of Image Forming Apparatus&gt; 
       FIG. 1  is a schematic cross-sectional diagram of an image forming apparatus  1  relating to the present embodiment. Firstly, the general configuration of the image forming apparatus  1  will be described with reference to  FIG. 1 . The image forming apparatus  1  is a color laser printer, and a cassette  11  loaded with recording paper is provided in the lower portion of the image forming apparatus  1  so as to be insertable in an apparatus main body. The recording paper loaded in the cassette  11  is separated and paid out, one sheet at a time, by a pick-up roller  12  and paper supply roller  13 , and is conveyed by a conveyance roller pair  14  and a conveyance roller pair  15  towards a secondary transfer roller  25 . Furthermore, the conveyance roller pair  15  has a registration function for synchronizing the toner image formed on the intermediate transfer belt  23 , and the recording material. 
     Moreover, the image forming apparatus  1  has four process cartridges  60  ( 60 Y,  60 M,  60 C,  60 K) (driven units) which can be attached in and removed from the apparatus main body of the image forming apparatus  1 . In  FIG. 1 , the process cartridges  60  are, arranged in order from the left-hand side, a process cartridge  60 Y (yellow), a process cartridge  60 M (magenta), a process cartridge  60 C (cyan) and a process cartridge  60 K (black). Here, in the present embodiment, the configuration of the process cartridges  60 Y to  60 K 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 scanner  21  forms an electrostatic latent image on a photosensitive drum  22  ( 22 Y to  22 K) by irradiating the photosensitive drum  22 , which has been charged by a charging roller, with a laser. Furthermore, the toner held inside the process cartridge  60  is supplied to a developing roller  66  (developer carrying member) by a supply roller  65  ( 65 Y to  65 K) which is a supply member (see  FIG. 2A  and  FIG. 2B ). The developing roller  66  carries toner. A developing bias is applied between the developing roller  66  and the photosensitive drum  22 , and the toner carried on the developing roller  66  is supplied to the photosensitive drum  22 , thereby developing the electrostatic latent image on the photosensitive drum  22 . 
     The toner images formed on the photosensitive drums  22  are primarily transferred onto the intermediate transfer belt  23  by the application of a bias to the primary transfer rollers  24  ( 24 Y to  24 K). 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 belt  23 . Furthermore, the toner image of four colors on the intermediate transfer belt  23  is transferred secondarily onto the recording material by a secondary transfer roller  25 , 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 roller  31 . 
     The recording material on which the toner image has been fixed is then discharged to a paper discharge tray  34  situated outside the image forming apparatus  1 , by a discharge roller  32 . Furthermore, when forming an image on both surfaces of the recording material, the recording material is switched back by a reversal roller  33 , and is conveyed again to the conveyance roller pair  15  by the conveyance roller pair  41  and the conveyance roller pair  42 . 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 tray  34 . 
     &lt;Configuration of Process Cartridge&gt; 
     Next, the configuration of the process cartridge  60  will be described with reference to  FIG. 2A  and  FIG. 2B .  FIG. 2A  and  FIG. 2B  are schematic cross-sectional drawings of a process cartridge  60  viewed in the direction of the axis of rotation of the photosensitive drum  22 . As shown in  FIG. 2A , the process cartridge  60  has a photosensitive body unit  63  having a photosensitive drum  22 , and a developing unit  64  having a developing roller  66  and a supply roller  65 . The image forming apparatus  1  is provided with a frame  51 , which is one portion of the framework of the apparatus. The frame  51  is a plate-shaped metal member (metal plate) which extends in the vertical direction and in the direction of arrangement of the plurality of photosensitive drums  22 . The photosensitive drum  22  is positioned with respect to the frame  51  by being pressed by pressing means (not illustrated) in the direction of arrow A towards a positioning portion  53  of the frame  51 , via a bearing  69  (bearing member) for the photosensitive drum  22 . The photosensitive body unit  63  is registered in position by fitting together of a rotation stopping portion  67 , which is a fitting portion, and a fit receiving portion (not illustrated) which is provided in the frame  51 . Furthermore, the developing unit  64  is supported rotatably about a swinging shaft  68 , with respect to the photosensitive body unit  63 . 
     The developing roller  66  is impelled by impelling means (not illustrated) in a direction towards the photosensitive drum  22 . When developing the electrostatic latent image on the photosensitive drum  22 , the developing roller  66  makes contact with the photosensitive drum  22 , as shown in  FIG. 2A . On the other hand, when not developing the electrostatic latent image on the photosensitive drum  22 , as shown in  FIG. 2B , the photosensitive drum  22  and the developing roller  66  are set to a separated state, due to the developing unit  64  being pressed in the X direction by a separating member  91 . 
       FIG. 3  is a cross-sectional diagram of the developing unit  64  and the drive transmission mechanism  90  of the image forming apparatus  1 , as viewed in a direction perpendicular to the direction of the axis of rotation of the supply roller  65 . In the developing unit  64 , as shown in  FIG. 3 , the drive transmitted to the drive receiving member (driving force receiving portion)  61  can be transmitted to the supply roller  65  via a joint  62 . The driving force transmitted to the supply roller  65  is transferred to the developing roller  66  via a gear (not illustrated). 
     When an electrostatic latent image on the photosensitive drum  22  is not being developed in the process cartridge  60  as described above, then the photosensitive drum  22  and the developing roller  66  are separated from each other. It will now be explained why it is necessary to separate the photosensitive drum  22  and the developing roller  66 . If a toner image is formed on the photosensitive drum  22 , firstly, the photosensitive drum  22  rotates in a state where the photosensitive drum  22  and the developing roller  66  are separated. The photosensitive drum  22  is irradiated with a laser from the scanner  21 , thereby forming an electrostatic latent image on the photosensitive drum  22 . 
     Next, the developing roller  66  is made to contact the photosensitive drum  22 , in a state where the developing roller  66  and the supply roller  65  are rotating. By applying a bias to the developing roller  66  in a state where the photosensitive drum  22  and the developing roller  66  are in contact with each other, the electrostatic latent image on the photosensitive drum  22  is developed. Here, the photosensitive drum  22  and the developing roller  66  rotate at different speeds of rotation. Therefore, when the rotating photosensitive drum  22  and the rotating developing roller  66  make contact, rubbing occurs between the photosensitive drum  22  and the developing roller  66 , leading to abrasion and wearing of the photosensitive drum  22  and the developing roller  66 . This abrasion and wearing shorten the life of the photosensitive drum  22  and the developing roller  66 . Consequently, by reducing the rubbing time between the photosensitive drum  22  and the developing roller  66 , it is possible to lengthen the life of the photosensitive drum  22  and the developing roller  66 . Therefore, the photosensitive drum  22  and the developing roller  66  are separated when not developing an electrostatic latent image. 
     However, since the photosensitive drum  22  and the developing roller  66  may be in a separated state, then there may be cases where drive is transmitted to the developing roller  66  in this separated state. When the photosensitive drum  22  and the developing roller  66  are in a separated state, the positions of the rotational center axis  72 A of the drive coupling member (driving force transmission rotating body)  72  (see  FIG. 3 ) and the rotational center axis of the supply roller  65  deviate while maintaining a parallel relationship. The joint  62  is provided in the process cartridge  60  in such a manner that drive is transmitted to the supply roller  65  even in this state. In the present embodiment, an Oldham coupling is used as the joint  62 , but the joint  62  may also be a disk coupling, or the like. Here, as shown in  FIG. 3 , the process cartridge  60  has a drive receiving member  61  and a joint  62 . The drive receiving member  61  has a driving force receiving portion  61   a , and by engagement of the driving force receiving portion  61   a  and the drive coupling portion  72   a  of the drive coupling member  72 , drive is transmitted from the drive coupling member  72  to the drive receiving member  61 . The joint  62  can transmit drive from the drive coupling member  72  to the supply roller  65 , even if there is deviation between the rotational center axis  72 A of the drive coupling member  72  and the rotational center axis of the supply roller  65 . 
     &lt;Configuration for Transmitting Drive to Process Cartridge&gt; 
     Next, the mechanism for transmitting drive to the process cartridge  60  will be described with reference to  FIG. 3  to  FIG. 5 .  FIG. 3  is a cross-sectional drawing illustrating a mechanism for transmitting driving force to the process cartridge  60  according to a first embodiment of the invention.  FIG. 4  is a cross-sectional diagram showing the state of a drive input rotating body  70  in a case where the process cartridge  60  has been removed.  FIG. 5  is a diagram showing a state where the photosensitive drum  22  has been positioned on the frame  51 . 
     As shown in  FIG. 3 , the drive transmission mechanism  90  includes the frame  51 , a cylindrical projecting portion  52  which is provided to project in the main body portion of the frame  51 , and the drive input rotating body  70  which is supported rotatably on the projecting portion  52 . Furthermore, the drive input rotating body  70  includes the drive transmission member  71  and the drive coupling member  72 . The drive transmission member  71  has a drive transmission portion  71   a , which is a gear tooth surface, and the drive coupling member  72  has a drive coupling portion  72   a  for transmitting drive to the process cartridge  60 . 
     When drive means (not illustrated) is driven, driving force is transmitted to the drive transmission member  71  due to a gear (not illustrated) engaging with the drive transmission portion  71   a . Due to the engagement of the drive transmission member  71  and the drive coupling member  72 , the driving force transmitted to the drive transmission member  71  is transmitted to the drive coupling member  72 . A groove (not illustrated) is provided in the drive transmission member  71 , and a rib (not illustrated) is provided in the drive coupling member  72 . The rib provided in the drive coupling member  72  engages with the groove provided in the drive transmission member  71 , whereby the driving force is transmitted from the drive transmission member  71  to the drive coupling member  72 . 
     The driving force transmitted to the drive coupling member  72  is transmitted to the drive receiving member  61 . A groove-shaped drive coupling portion  72   a  is provided in the drive coupling member  72 , and a driving force receiving portion  61   a , which is a rib, is provided in the drive receiving member  61 . Due to the drive coupling portion  72   a  provided on the drive coupling member  72  engaging with the driving force receiving portion  61   a  provided on the drive receiving member  61 , driving force is transmitted from the drive coupling member  72  to the drive receiving member  61 . Furthermore, similarly, a rib (not illustrated) is provided on the drive receiving member  61  and a groove (not illustrated) is provided in the joint  62 . The rib provided on the drive receiving member  61  engages with the groove provided in the joint  62 , whereby the driving force is transmitted from the drive receiving member  61  to the drive joint  62 . 
     In this way, in the present embodiment, the drive input rotating body  70  includes the drive transmission member  71  and the drive coupling member  72 . Here, the drive transmission member  71  is positioned by a shaft  75 , and the drive coupling member  72  is positioned by the projecting portion  52 . Supposing that the drive transmission member  71  and the drive coupling member  72  are formed by a single member as the drive input rotating body  70 , then if there is deviation in the position where the axis of rotation of the drive input rotating body  70  is supported, the drive input rotating body  70  is rotated in an inclined state. 
     When the drive input rotating body  70  is rotated in an inclined fashion, rotational non-uniformities occur in the supply roller  65 , since the drive ceases to be transmitted satisfactorily from the drive input rotating body  70  to the drive receiving member  61 , and there is a risk of deterioration in the image quality. However, in the present embodiment, the drive input rotating body  70  is configured by mutual engagement of separate members, namely, the drive transmission member  71  and the drive coupling member  72 . Due to the occurrence of play between the drive transmission member  71  and the drive coupling member  72 , it is possible to transmit drive from the drive transmission member  71  and the drive coupling member  72 , without inclination of the drive transmission member  71 . Consequently, it is possible to suppress inclination of the tooth surface of the drive transmission portion  71   a  (gear) in the drive transmission member  71 , 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 portion  52  is formed in the frame  51 . The cylindrical projecting portion  52  supports the drive coupling member  72  in a rotatable fashion. Furthermore, the central axis  52 A of the cylindrical projecting portion  52  coincides with the rotational center axis  72 A of the drive coupling member  72 . The circumferential surface  52   s  of the cylindrical projecting portion  52  supports the drive coupling member  72  rotatably about the rotational center axis  72 A. As shown in  FIG. 3 , the circumferential surface  52   s  is the inner circumferential surface of the cylindrical projecting portion  52 . In the present embodiment, the projecting portion  52  is formed on the frame  51  by which the photosensitive drum  22  is positioned in the process cartridge  60 . Furthermore, the frame  51  and the projecting portion  52  are made from a metallic material. The material of the frame  51  is not necessarily limited to this. The frame  51  and the projecting portion  52  may be, for example, made from a resin material which has excellent strength and heat resistance. For example, the frame  51  may 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 frame  51  is made from a metallic material. Consequently, it is possible to improve the heat conductivity of the frame  51 , compared to a case where the frame  51  is made from a resin material. In the present embodiment, the photosensitive drum  22  and the developing roller  66  are in a separated state in the process cartridge  60 , except when forming an image. In this separated state, drive is transmitted from the drive coupling member  72  to the supply roller  65 , in a state where there is great deviation between the central axes of rotation of the drive coupling member  72  and the supply roller  65 . Consequently, a load is applied to the drive coupling member  72  in a direction perpendicular to the direction of the rotational center axis of the drive coupling member  72 . 
     Furthermore, in recent years, the speed of image formation in an image forming apparatus  1  has been increasing. In accordance with this, the speed of rotation of the drive coupling member  72  has become dramatically faster. When the load on the drive coupling member  72  and the speed of rotation of the drive coupling member  72  are high, abrasion and wear occurs in the drive coupling member  72  due to increase in the temperature of the rubbing portions of the drive coupling member  72  and the projecting portion  52 , as a result of the heat of friction. 
     Furthermore, if the frame  51  is made from resin, there is a risk of burning of the frame  51  if the temperature in the rubbing portions of the drive coupling member  72  and the projecting portion  52  becomes higher than the thermal resistance temperature of the resin. Consequently, by forming a frame  51  from 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 member  72  and the projecting portion  52 , and the occurrence of abrasion or wear, or burning, etc. in the frame  51 , can be suppressed. Furthermore, although a large load is applied to the projecting portion  52 , by using a metallic plate material which has greater rigidity than a resin material as the material of the frame  51 , it is possible to suppress the occurrence of elastic deformation and/or creep in the projecting portion  52 , and to position the drive coupling member  72  accurately. 
     Furthermore, in the present embodiment, the cylindrical projecting portion  52  is formed by a burring process. The drive transmission member  71  is supported rotatably by the shaft  75 , and furthermore, the drive coupling member  72  is supported movably in the direction of the rotational center axis of the drive coupling member  72 . The drive coupling member  72  is disposed on the side nearer to the process cartridge  60  than the drive transmission member  71  (the side of the driven unit). Furthermore, an impelling member  76  is attached on the drive transmission member  71  and the drive coupling member  72 , thereby impelling the drive coupling member  72  towards the process cartridge  60 . 
     Next, the positional relationship between the drive coupling member  72  and the projecting portion  52  in a state where the process cartridge  60  has been removed from the image forming apparatus  1  will be described.  FIG. 4  is a cross-sectional drawing showing the vicinity of the drive coupling member  72 , when the process cartridge has been removed, as viewed in a direction perpendicular to the rotational center axis  72 A. The process cartridge  60  is removed from the image forming apparatus  1  in a direction B 1  parallel to the rotational center axis  72 A, away from the drive transmission member  71  with respect to the frame  51 . 
     Here, the drive coupling member  72  can be moved with respect to the projecting portion  52 , in the direction of the rotational center axis  72 A of the drive coupling member  72 . In  FIG. 4 , the drive coupling member  72  can be moved in the direction of B 1  and the direction of B 2  which is opposite to B 1 . When the process cartridge  60  and the drive coupling member  72  are in an engaged state, then as shown in  FIG. 3 , the drive coupling member  72  moves in the direction of B 1 , and thereby moves to the side where the drive receiving member  61  of the process cartridge  60  is disposed. In a state where the drive coupling member  72  has been moved to the side where the drive receiving member  61  of the process cartridge  60  is disposed, the drive coupling member  72  and the drive receiving member  61  can be engaged with each other. Due to the drive coupling member  72  moving in the direction B 1  when the process cartridge  60  has been attached on the image forming apparatus  1 , the drive coupling member  72  moves towards the process cartridge  60 , and the driving force receiving portion  61   a  and the drive coupling portion  72   a  engage with each other. 
     Furthermore, as shown in  FIG. 4 , the drive coupling member  72  can also be moved in a direction B 2  which is opposite to the side where the process cartridge  60  is disposed. When the process cartridge  60  is removed from the image forming apparatus  1 , as shown in  FIG. 4 , the drive coupling member  72  moves in the direction B 2 , moves towards the drive transmission member  71 , and abuts against the shaft  75 . In the present embodiment, even if the drive coupling member  72  has moved to the side of the drive transmission member  71 , as shown in  FIG. 4 , the drive coupling member  72  still projects out to the side where the drive receiving member  61  of the process cartridge  60  is disposed (the downstream side in direction B 1 ), beyond the front end of the projecting portion  52 , in the direction of the rotational center axis  72 A. Here, the end portion of the drive coupling member  72  on the side where the drive receiving member  61  of the process cartridge  60  is disposed, in the direction of the rotational center axis  72 A of the drive coupling member  72 , is called end portion  72 B. In the present embodiment, in the direction of the rotational center axis  72 A of the drive coupling member  72 , the end portion  72 B is positioned closer to the side where the drive receiving member  61  of the process cartridge  60  is disposed (the downstream side in direction B 1 ), than the front end  52 B of the projecting portion  52  in the direction of the central axis  52 A of the projecting portion  52  is positioned. 
     In the present embodiment, when the process cartridge  60  is removed from the image forming apparatus  1 , a user may directly touch the drive coupling member  72  or the cylindrical projecting portion  52 , etc. Therefore, it is desirable if the frame  51  is made from a hard material, such as a metallic material, thereby making the user less liable to touch the edges of the front end  52 B of the cylindrical projecting portion  52 . 
     Furthermore, the drive coupling member  72  can be moved between a transmission position, which is a position for when transmitting drive by engaging with the drive receiving member  61 , and a retracted position, which is a position withdrawn (moved) in the B 2  direction (a direction away from the drive receiving member  61 ), from the transmission position. Furthermore, at least the surface of the drive coupling member  72  is made from a resin material. However, as shown in  FIG. 4 , even in a state where the drive coupling member  72  is situated in the retracted position, the drive coupling member  72  projects towards the drive receiving member  61  in the process cartridge  60 , with respect to the front end  52 B of the projecting portion  52 , in the direction of the rotational center axis  72 A. Consequently, it is possible to make the user less liable to touch the edges of the front end  52 B of the projecting portion  52 . 
     Next, the positional relationship between the components that constitute the process cartridge  60 , and the frame  51 , will be described.  FIG. 5  is a diagram showing a state where the photosensitive drum  22  has been positioned on the frame  51 , and the developing roller  66  has been placed in contact with the photosensitive drum  22 . As described above, the photosensitive drum  22  is positioned with respect to the frame  51  by abutting against the positioning portion  53  in the frame  51  via the bearing  69  for the photosensitive drum  22 . A cutaway region (cutaway hole)  54  which is larger than the bearing  69  for the photosensitive drum  22  is formed in the frame  51 , which is made of plate metal. The cutaway portion  54  is a portion which is cut out from the frame  51 . The edge of the cutaway portion  54  forms a positioning portion  53 . In other words, in the present embodiment, the photosensitive drum  22  in the process cartridge  60  is positioned on the frame  51 , and the projecting portion  52  is formed integrally with a portion of the frame  51 . The circumferential surface  52   s  of the projecting portion  52  indicated by the dotted line in  FIG. 5  is a circumferential surface which is coaxial with the supply roller  65 . 
     In this way, in the present embodiment, the process cartridge  60  is positioned by the positioning portion  53  in the frame  51 , and the drive coupling member  72  is supported rotatably by the projecting portion  52  in the frame  51 . By supporting the drive coupling member  72  on the frame  51  which positions the process cartridge  60 , without any other intervening components, it is possible to improve the positioning accuracy of the drive coupling member  72  with respect to the process cartridge  60 . 
     Consequently, it is possible to suppress deviation between the rotational center axis of the drive receiving member  61  in the process cartridge  60  and the rotational center axis  72 A of the drive coupling member  72 , and rotational non-uniformity in the rotating body that is used in the process cartridge  60  can be suppressed. Furthermore, by supporting the drive coupling member  72  with the frame  51 , without an intervening bearing, then it is possible to reduce the number of components used in the image forming apparatus  1  and the costs can be lowered. 
     Since rotational non-uniformity of the rotating body used in the process cartridge  60  can be suppressed, it is possible to effectively suppress density non-uniformity in the image formed on the recording medium. In the process cartridge  60 , 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 drum  22 , 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 cartridge  60  and/or intermediate transfer belt  23 , 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 mechanism  90  which transmits drive to the process cartridge  60 , 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 cartridge  60 , 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 cartridge  60  by using the minimum necessary members. For example, in the developing unit  64 , by transmitting drive to the developing roller  66  by a drive transmission member  71  which is supported on the projecting portion  52 , it is thought that the number of components used in the process cartridge  60  can be reduced. 
     In this case, as shown in  FIG. 5 , a cutaway portion  54  is formed in the frame  51  and constitutes a positioning portion  53  by which the bearing  69  supporting the rotational shaft of the photosensitive drum  22  is positioned. When the drive coupling member  72  is disposed on the rotational center axis of the developing roller  66 , the cutaway portion  54  and the projecting portion  52  overlap with each other in the frame  51 , and therefore it is not possible to form a cylindrical projecting portion  52  in the frame  51 . In the present embodiment, the drive coupling member  72  transmits drive to the supply roller  65  which is disposed at a position sufficiently distanced from the cutaway portion  54 . Therefore, it is possible to support the drive coupling member  72  rotatably by the projecting portion  52 . 
     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 surface  52   s  of 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 surface  52   s  centered on the rotational center axis  72 A is formed only in a portion of the circumferential direction, such that the circumferential surface  52 s can rotatably support the drive coupling member  72 . 
     (Second Embodiment) 
     Next, a second embodiment will be described with reference to  FIG. 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 mechanism  85 , a constricted portion  83  formed bya constricting process is provided on the frame  81  which is made from plate metal, and a cylindrical projecting portion  82  is formed in the vicinity of the center of the constricted portion  83 . A circular circumferential surface  82   s  which is centered on a central axis  82 A coinciding with the rotational center axis  72 A is formed on the projecting portion  82 , and the circular circumferential surface  82   s  rotatably supports the drive coupling member  72 . 
     The constricted portion  83  is formed in a concave shape on the side where the process cartridge  60  is not disposed, and is formed in a convex shape on the side where the process cartridge  60  is disposed. In the present embodiment, the front end  82 B of the projecting portion  82  in the direction of the central axis  82 A of the cylindrical projecting portion  82  projects in the opposite direction from the side where the process cartridge  60  is disposed. The cylindrical projecting portion  82  supports the drive coupling member  72  in 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. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     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.