Abstract:
An image forming apparatus includes a process unit detachably mountable to a main assembly of the apparatus, the process unit including an image bearing member for bearing an electrostatic image and process means actable on the image bearing member, the process means having a rotational shaft; a driving shaft, substantially co-axial with the rotational shaft, for rotating the rotational shaft; and a drive transmitting member, engaged with the driving shaft and with the rotational shaft, for transmitting a driving force to the rotational shaft from the driving shaft; wherein the drive transmitting member is engaged with the driving shaft with a play and is engaged with the rotational shaft with a play.

Description:
FIELD OF THE INVENTION AND RELATED ART  
         [0001]    The present invention relates to an image forming apparatus.  
           [0002]    The service life of the image bearing member, or the like, of an image forming apparatus is shorter than that of the main assembly of the image forming apparatus. Therefore, it is a common practice to render the image forming member or the like exchangeably mountable in the main assembly by placing it in a cartridge, or a so-called process cartridge.  
           [0003]    A process cartridge needs to receive driving force from the main assembly of an image forming apparatus in which it is mounted.  
           [0004]    In one of the methods for transmitting driving force from the main assembly of an image forming apparatus to a process cartridge, the drive shaft on the process cartridge side is directly connected to the drive shaft on the apparatus main assembly side, eliminating the need for driving force transmission gears. In other words, driving force is transmitted through a simple structure.  
           [0005]    However, if a process cartridge is provided with a plurality of members to be driven by the driving force transmitted thereto from the apparatus main assembly side, it is rather difficult to accurately position the drive shafts of the plurality of members on the process cartridge side so that they perfectly align with the corresponding drive shafts on the apparatus main assembly side.  
           [0006]    In a structural arrangement in which a drive shaft is connected to a drive shaft in a virtually straight line as described above, if the position of a drive shaft on the driving side, or a driving shaft, and the position of a drive shaft on the driven side, or a driven shaft, are misaligned in terms of the axial direction of the drive shaft and driven shaft before they are connected, the two shafts become connected in such a manner that their rotational axes remain slanted relative to each other. Such connection makes the contact points between the two shafts nonuniform in terms of the amount of the driving force transmitted through each contact point. As a result, a certain amount of driving force is diverted from the direction in which the driving force is to be transmitted, causing a process cartridge to vibrate.  
         SUMMARY OF THE INVENTION  
         [0007]    The primary object of the present invention is to provide an image forming apparatus, in which even if the shafts of the plurality of components within a process cartridge having been removably mounted in the main assembly of the image forming apparatus, are not in perfect alignment with the corresponding drive shafts on the apparatus main assembly side, driving force is transmitted from the driving shafts, or the drive shafts on the main assembly side, to the shafts to be drive, or the shafts on the process cartridge side, without causing vibrations.  
           [0008]    According to an aspect of the present invention, there is provided an image forming apparatus comprising: a process unit detachably mountable to a main assembly of said apparatus, said process unit including an image bearing member for bearing an electrostatic image and process means actable on said image bearing member, said process means having a rotational shaft; a driving shaft, substantially co-axial with said rotational shaft, for rotating said rotational shaft; and a drive transmitting member, engaged with said driving shaft and with said rotational shaft, for transmitting a driving force to said rotational shaft from said driving shaft, wherein said drive transmitting member is engaged with said driving shaft with a play and is engaged with said rotational shaft with a play.  
           [0009]    According to another aspect of the present invention, there is provided a process cartridge detachably mountable to an image forming apparatus, said process cartridge comprising an image bearing member for bearing an electrostatic image; process means actable on said image bearing member, said process means including a rotational shaft; and a drive transmitting member for receiving a driving force from a driving shaft provided in a main assembly of the apparatus; wherein said drive transmitting member is engageable with said driving shaft with a play and is engaged with said rotational shaft with a play.  
           [0010]    According to a further aspect of the present invention, it is preferable that in said apparatus, said image bearing member has a rotational shaft which is engaged with a driving shaft provided in the main assembly of the apparatus with a play which is smaller than the play with which said drive transmitting member is engaged with said driving shaft or with said rotational shaft.  
           [0011]    According to a further aspect of the present invention, it is preferable that in said process cartridge, said image bearing member has a rotational shaft which is engageable with a driving shaft provided in the main assembly of the apparatus with a play which is smaller than the play with which said drive transmitting member is engaged with said driving shaft or with said rotational shaft.  
           [0012]    These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is a sectional view of the driving force transmitting apparatus in the first embodiment of the present invention, at a plane D-D (line D-D in FIG. 14), for showing the structure thereof.  
         [0014]    [0014]FIG. 2 is a sectional view of the driving force transmitting apparatus in the first embodiment of the present invention, at a plane E-E (line E-E in FIG. 14), for showing the structure thereof.  
         [0015]    [0015]FIG. 3 is a sectional view of the driving force transmitting portion of the driving force transmitting apparatus in the first embodiment of the present invention, for showing the movement thereof.  
         [0016]    [0016]FIG. 4 is a sectional view of the driving force transmitting portion of the driving force transmitting apparatus, at a plane B-B in FIG. 3.  
         [0017]    [0017]FIG. 5 is a sectional view of the driving force transmitting apparatus in the first embodiment of the present invention, in which the rotational axis of the driving shaft of the driving force transmitting apparatus is not in perfect alignment with the rotational axis of the sleeve shaft.  
         [0018]    [0018]FIG. 6 is a sectional view of the driving force transmitting portion of the driving force transmitting apparatus in the first embodiment of the present invention, for analytically showing different aspects of the driving force transmission.  
         [0019]    [0019]FIG. 7 is a sectional view of the driving force transmitting apparatus in the first embodiment of the present invention, at a plane C-C (line C-C) in FIG. 6.  
         [0020]    [0020]FIG. 8 is a rough side view of the coupling of the driving force transmitting apparatus, and the driving shaft, in the first embodiment of the present invention, for depicting process through which the two component engage with each other.  
         [0021]    [0021]FIG. 9 is a rough side view of the coupling (in sectional view) of the driving force transmitting apparatus, and the driving shaft, in the first embodiment of the present invention, for depicting the process through which the two components engage with each other.  
         [0022]    [0022]FIG. 10 is a phantom view of another version of the coupling of the driving force transmitting apparatus in the first embodiment of the present invention.  
         [0023]    [0023]FIG. 11 is a phantom view of the another version of the coupling of the driving force transmitting apparatus in the first embodiment of the present invention.  
         [0024]    [0024]FIG. 12 is a sectional view of the coupling portion of the driving force transmitting apparatus in the first embodiment of the present invention, for showing the method for fitting a pin into the driving shaft of the driving force transmitting apparatus, and for retaining the pin therein.  
         [0025]    [0025]FIG. 13 is a sectional view of an image forming apparatus (full-color copying machine) in accordance with the present invention.  
         [0026]    [0026]FIG. 14 is a sectional view of the image forming portion of the image forming apparatus in accordance with the present invention.  
         [0027]    [0027]FIG. 15 is a sectional view of the image forming portion and its drive train in the image forming apparatus in accordance with the present invention.  
         [0028]    [0028]FIG. 16 is an exploded perspective view of a drum cylinder and a drum shaft, for showing the structure for fixing the two components to each other.  
         [0029]    [0029]FIG. 17 is a sectional view of the drum cylinder, drum shaft, and their adjacencies, after the two components have been fixed to each other.  
         [0030]    [0030]FIG. 18 is a sectional view of the drum cylinder and drum shaft, which are coincident in rotational phase, but are in separation.  
         [0031]    [0031]FIG. 19 is a sectional view of the drum cylinder and drum shaft, at a plane H-H in FIG. 18.  
         [0032]    [0032]FIG. 20 is a side view of the drum cylinder and drum shaft.  
         [0033]    [0033]FIG. 21 is a plan view of the drum cylinder and drum shaft.  
         [0034]    [0034]FIG. 22 is a sectional view of the driving force transmitting portion of the driving force transmitting apparatus in the second embodiment of the present invention, at the vertical plane inclusive of the axial line of the driving force transmitting portion, for showing the structure thereof.  
         [0035]    [0035]FIG. 23 is a sectional view of the driving force transmitting portion of the second embodiment of the driving force transmitting apparatus in accordance with the present invention, at the plane F-F in FIG. 22.  
         [0036]    [0036]FIG. 24 is a sectional view of the driving force transmitting portion of the second embodiment of the driving force transmitting apparatus in accordance with the present invention, at the plane F-F in FIG. 22.  
         [0037]    [0037]FIG. 25 is a sectional view of the driving force transmitting portion of the second embodiment of the driving force transmitting apparatus in accordance with the present invention, at the plane G-G in FIG. 22.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    Hereinafter, the preferred embodiments of the present invention will be described with reference to the appended drawings. &lt;Embodiment 1&gt; 
         [0039]    [0039]FIG. 13 is a vertical sectional view of a full-color copying machine as an image forming apparatus in accordance with the present invention. This full-color image forming apparatus is such an apparatus that forms a full-color image by placing in layers four toner images different in color, that is, yellow, magenta, cyan and black toner images.  
         [0040]    Referring to FIG. 13, referential codes  10 Y,  10 M,  10 C and  10 K designate yellow, magenta, cyan and black toner image forming stations. FIG. 14 is an enlarged sectional view of one of the image forming stations.  
         [0041]    A plurality of sheets of recording paper are stored in a cassette  1 , and are fed out of the cassette  1  into the main assembly of the image forming apparatus in a sheet feeding station  2 . Then, the recording paper conveyed to a registration roller  3 , by which the recording paper is rectified in alignment or the like, if it is askew or in the like conditions, and then, is released to be conveyed to a transfer belt  4  with a proper timing. Meanwhile, a latent image is formed on each of the photosensitive drums  11 Y,  11 M,  11 C and  11 K, by signals which reflect image formation data sent from the output apparatus (unshown) of an unshown reading apparatus or computer.  
         [0042]    After being released by the registration roller  3 , the recording paper is electrostatically adhered to a transfer belt  4 , and is conveyed by the transfer belt  4 , passing under the image forming stations  10 Y,  10 M,  10 C and  10 K.  
         [0043]    In the image forming stations  10 Y,  10 M,  10 C and  10 K, LED heads  12 Y,  12 M,  12 C and  12 K, developing apparatuses  13 Y,  13 M,  13 C and  13 K, and charging devices  14 Y,  14 M,  14 C and  14 K are disposed in a manner to surround the peripheral surfaces of the photosensitive drums  11 Y,  11 M,  11 C and  11 K, correspondingly, and yellow, magenta, cyan and black toner images, are formed on the peripheral surfaces of the photosensitive drums  10 Y,  10 M,  10 C and  10 K, correspondingly, through an electrophotographic process. These toner images are consecutively transferred onto the recording paper by the functions of the transferring means  5 Y,  5 M,  5 C and  5 K. In the transfer station, in which the transfer belt  4  comes virtually in contact with the photosensitive drums  11 Y,  11 M,  11 C and  11 K.  
         [0044]    After the four color toner images are transferred onto the recording paper, the transfer paper is separated from the transfer belt, based on the resiliency of the recording paper and the curvature of the transfer belt  4 , and is conveyed to a fixing station  6 , in which the toner images are fixed to the recording paper with the application of heat and pressure. Thereafter, the recording paper is discharged into a delivery tray  7 , ending a single cycle of a copying operation.  
         [0045]    Next, referring to FIGS. 14 and 15, a process cartridge  21  will be described. FIG. 15 is a rough sectional view of the process cartridge and driving train therefor, for showing the structure thereof.  
         [0046]    The process cartridge  21  comprises a photosensitive drum  11 , a developing device  13 , and an injection type charging device  14 , which are integrally supported by the side plates  22  and  23  of the process cartridge  21  as shown in FIG. 15. This image forming apparatus is configured so that the process cartridge  21  can be removably mountable in the main assembly of the image forming apparatus in the front-to-rear direction of the image forming apparatus; in other words, all, one, or some of the components disposed within the process cartridge can be replaced or maintained to maintain the image forming apparatus.  
         [0047]    The position of the photosensitive drum  11  relative to the side walls  22  and  23  is not fixed; it becomes fixed as the photosensitive drum  11  is fitted around the drum shaft  51  when the process cartridge  21  is mounted into the apparatus main assembly. In comparison, the positions of the developing device  13  and injection type charging device  14  relative to the side plates  22  and  23  are fixed. More specifically, fitting a pin  23   a  projecting from the side plate  23  in one end (smaller diameter portion) of the elongated hole  52   a  of the side plate  52  on the main assembly side after fitting the drum shaft  51  into the bearing portions  24  and  25  of the side plates  22  and  23 , respectively, fixes the positional relationship between the side plates  22  and  23  and developing device  13 , as well as the positional relationship between the side plates  22  and  23  and the injection type charging device  14 .  
         [0048]    As for the development sleeve  13   a  of the developing device  13  and the injection sleeve  14   a  of the injection type charging device  14 , their distances from the bearings  24  and  25  are precisely adjusted when they are attached to the side plates  22  and  23 . Thus, the positional relationships between the development sleeve  13   a  and the drum shaft  51 , and between the injection sleeve  14   a  and the drum shaft  51 , in terms of the radius direction of the photosensitive drum  11 , are highly precisely fixed as the process cartridge  21  is mounted into the apparatus main assembly. Further, since the position of the photosensitive drum  11  is also fixed relative to the drum shaft  51 , the clearance (SD gap) between the peripheral surfaces of the development sleeve  13   a  and photosensitive drum  11 , and the clearance (SC gap) between the peripheral surfaces of the photosensitive drum  11  and injection sleeve  14   a , are highly precisely set.  
         [0049]    Referring to FIG. 15, the drive shafts  81  and  91  are for driving the development sleeve  13   a  and injection sleeve  14   a , respectively. They are disposed so that they will be connected in a straight line with the rotational shafts of the development sleeve  13   a  and injection sleeve  14   a  as the process cartridge  21  is mounted into the apparatus main assembly. The drive shafts  81  and  91  are equipped with electromagnetic clutches  83  and  93 , respectively, so that they can be rotated with their own predetermined timings. The development sleeve  13   a  and injection sleeve  14   a  are fitted with couplings  61  and  71 , which are on the clutch side, and through which driving force is transmitted to the development sleeve  13   a  and injection sleeve  14   a  from the drive shafts  81  and  91 , respectively.  
         [0050]    Next, the structure of the driving force transmitting portion will be described in detail.  
         [0051]    [0051]FIG. 1 is a sectional view of the development sleeve and the drive shaft therefor, at a plane D-D (line D-D in FIG. 14). FIG. 2 is a sectional view of the development sleeve and drive shaft therefor, at a plane A-A in FIG. 1 (line E-E in FIG. 14). Since the structure of the injection type charging device  14  is the same in the structure of the driving force receiving portion as the developing device  13 , only the structure of the driving force transmitting portion of the developing device  13  will be described.  
         [0052]    The drive shaft  81 , and the sleeve shaft  31  of the development sleeve  13   a , are provided with pins  82  and  32 , which project from the peripheral surfaces of the drive shaft  81  and sleeve shaft  31 , respectively. The coupling  61  is provided with a groove  61   a  and a hole  61   b , the positions of which correspond to the positions of the pins  82  and  32 , respectively. Driving force is transmitted by the engagements between the pins  81  and groove  61   a , and between the pins  32  and holes  61   b . The reason why the holes  61   b  of the coupling  61  are positioned on the sleeve shaft  31  side, and the grooves  61   a  of the coupling  61 , which opens toward the shaft  81 , are positioned on the drive shaft  81  side, is that the coupling  61  is to be permanently attached to the sleeve shaft  31 , and is to be enabled to be connected to, or disconnected from, the drive shaft  81 .  
         [0053]    The coupling  61  is provided with cylindrical portions  61   c  and  61   d , into the hollows of which the ends of the drive shaft  81  and sleeve shaft  31  are inserted, respectively. The external diameter d1 of the drive shaft  81  is 6 mm, whereas the internal diameter D1 of the cylindrical portion  61   c  of the coupling  61  is 7 mm. Further, the external diameter d2 of the sleeve shaft  31  is 8 mm, whereas the internal diameter D2 of the cylindrical portion  61   d  of the coupling  61  is 8.5 mm. Therefore, there are a relatively large amount of play between the drive shaft  81  and the internal surface of the coupling  61 , and also a relatively large amount of play between the sleeve shaft  31  and the internal surface of the coupling  61 , in terms of their radius direction. The pin  82  which is put through the drive shaft  81  is the same in diameter as the pin  32  which is put through the sleeve shaft  31 , and is 2 mm in diameter.  
         [0054]    Play is also provided between the pin  82  and the bottom of the groove  61   a , and between the pin  32  and the wall of the hole  61   b , in terms of the axial direction of the coupling  61 . The amount of the play δz1 in terms of the axial direction of the coupling  61  between the drive shaft  81  and the bottom of the groove  61   a  is 2 mm. The dimension z2 of the pin  32  of the sleeve shaft  31  in terms of the thrust direction of the coupling  61 , that is, the diameter of the pin  32 , is 2 mm, whereas the dimension z2 of the hole  61   b  in terms of the thrust direction of the coupling  61 , that is, the length of the long axis of the hole  61   b , is 3 mm. Therefore, there is a play of 0.5 mm between the pin  32  and each end of the hole  61   b  in terms of the thrust direction of the coupling  61 . The standard for this play is no less than 100 μm on each side of the pin  32 , or a total of no less than 200 μm.  
         [0055]    As described above, in this embodiment, a predetermined amount of play is provided between the drive shaft  81  and the internal surface of the coupling  61  in terms of the radius direction of the coupling  61 , and a predetermined amount of play is provided between the sleeve shaft  31  and the internal surface of the coupling  61  in terms of the radius direction of the coupling  61 . Further, a predetermined amount of play is provided between the pin  82  of the drive shaft  81  and the bottom of the groove  61   a  in terms of the axial direction of the coupling  61 , and a predetermined amount of play is provided between the pin  32  of the sleeve shaft  31  and the opposing ends of the hole  61   b , in terms of the axial direction of the coupling  61 . Therefore, the coupling  61  is allowed to wobble relative to the drive shaft  81  and sleeve shaft  31 .  
         [0056]    Referring to FIG. 3, and FIG. 4 (sectional view at line B-B in FIG. 3), give a rough depiction of the manner in which the coupling  61  is allowed to wobble. Referring to FIG. 3, in which the axis perpendicular to the plane of this drawing is designated by a referential code x; the vertical direction in this drawing is designated by a referential code y, and the horizontal direction in this drawing is designated by a referential code z, the coupling  61  is allowed to pivot about the axis x, relative to the sleeve shaft  31 . Referring to FIG. 4, the coupling  61  is allowed to pivot about the axis y, relative to the sleeve shaft  31 . Since the axes x and y are perpendicular to each other, the coupling  61  is allowed to wobble about the intersection O2 between the axial line of sleeve shaft  31  and the axial line of the pin  32  of the sleeve shaft  31 . Similarly, the coupling  61  is allowed to wobble about the intersection O1 between the axial line of the drive shaft  81  and the axial line of the pin  82  of the drive shaft  81 .  
         [0057]    [0057]FIG. 5 is a drawing for showing the positional relationship between the drive shaft  81  and sleeve shaft  31 , with the interposition of the coupling  61 , in which the axial lines of the two shafts are not in a straight line. As described before, the sleeve shaft  31  is not directly aligned with the drive shaft  81 . Therefore, there is a possibility that the sleeve shaft  31  will become misaligned from the drive shaft  81  by an amount equivalent to the sum of the tolerances of the components interposed between the sleeve shaft  31  and drive shaft  81 . In the case of the positional relationship between the sleeve shaft  31  and drive shaft  81  shown in FIG. 5, the amount of the misalignment e between the two shafts is 0.5 mm.  
         [0058]    Further, the angle θ (θ&lt;180 deg.) between the axial line of the driving force transmitting means, and the driving shaft or driven shaft, is approximately 2.2 deg. The range of the pivoting of the driving force transmitting means in terms of the angle relative to its radius direction is approximately 2.4 deg., and the range of the wobbling of the driving force transmitting means in terms of the angle relative to its axial line is approximately 4.8 deg. As is evident from the above description, since the range of the wobbling angle of the driving force transmitting means is rendered greater than the angle between the axial line of the driving force transmitting means and the axial line of the drive shaft or driven shaft, the driving force transmitting means is allowed to operate without interfering with the movements of the two shafts.  
         [0059]    In other words, in this embodiment, the drive shaft  81  and sleeve shaft  31  are indirectly connected to each other with the interposition of the coupling  61  which is allowed to wobble. Therefore, even if the drive shaft  81  and sleeve shaft  31  are not in alignment with each other, driving force is smoothly transmitted from the drive shaft  81  to the sleeve shaft  31  through the coupling  61 . Therefore, it does not occur that the process cartridge  21 , which is a unit to be driven, does not vibrates as driving force is transmitted thereto. Next, the reason why the process cartridge  21  does not vibrate even if the drive shaft  81  and sleeve shaft  31  are not in alignment with each other will be described in more detail.  
         [0060]    Referring to FIG. 5, when the drive shaft  81  is not in alignment with the sleeve shaft  31 , the coupling  61  becomes tilted. In this situation, the axial line of the coupling  61  intersects with both the intersection O1 of the axial lines of the pin  82  and drive shaft  81  and the intersection O2 of the axial lines of the pin  32  and sleeve shaft  31 .  
         [0061]    Thus, the coupling  61  is allowed to remain tilted while it rotates as the drive shaft  81  rotates, because the coupling  61  is allowed to pivot about the aforementioned two axes x and y, relative to the drive shaft  81  as described with reference to FIGS. 3 and 4. The relationship between the coupling  61  and sleeve shaft  31  are the same as that between the coupling  61  and drive shaft  81 .  
         [0062]    In this structural arrangement, the axial line of the drive shaft  81  intersects with the axial line L of the coupling  61  at the point at which drive force transmission occurs (contact point between pin  82  and the wall of the groove  61   a ), and the axial line of the sleeve shaft  31  intersects with the axial line L of the coupling  61  at the point at which driving force transmission occurs (contact point between pin  32  and the wall of the hole  61   b ). Therefore, a plurality of the contact points between the pin  82  and the wall of the groove  61 , and between the pin  32  and the wall of the hole  61   b , which are on the same cylindrical plane, and at which driving force is transmitted, become equal in the amount of driving force to be transmitted; driving force is evenly distributed among the plurality of driving force transmission points, as it is transmitted. Consequently, driving force, or torque, is simply transmitted as torque, without being partially turned into unwanted force, or the vibration causing force, as it is transmitted. Therefore, vibrations do not occur. As is evident from the above description, this embodiment can prevent driving force from being partially turned into the vibration causing force as it is transmitted, preventing therefore the driven unit from vibrating.  
         [0063]    In this embodiment, the groove  61   a  and hole  61   b  of the coupling  61  are differentiated from each other by 90 deg. in rotational phase. Next, the reason therefor will be described.  
         [0064]    Referring to FIGS. 3 and 4, attention will be paid to the movements of the sleeve shaft  31  and coupling  61  relative to each other. As shown in the drawings, the coupling  61  is pivotable about the axes x and y, relative to the sleeve shaft  31 . However, the pivotal movement of the coupling  61  about the axis x is different in dynamics from the pivotal movement of the coupling  61  about the axis y. More specifically, the pivotal movement of the coupling  61  relative to the sleeve shaft  31  shown in FIG. 3 involves the movements of the pin  32  and the hole  61   b  relative to each other, whereas the pivotal movement of the coupling  61  relative to the sleeve shaft  31  shown in FIG. 4 does not involve the movements of the pin  32  and hole  61   b  shown in FIG. 3. More specifically, the former causes the peripheral surface of the pin  32  and the wall of the hole  61   b  to slide against each other in the axial direction of the coupling  61 , whereas the latter causes the peripheral surface of the pin  32  and the wall of the hole  61   b  to slide against each other in the circumferential direction of the pin  32 . Thus, the former is greater in slide resistance (frictional resistance) than the latter.  
         [0065]    As the coupling  61  and sleeve shaft  31  rotate while being misaligned with each other, the state depicted in FIG. 3 and the state depicted in FIG. 4 alternately occur, causing the amount of the slide resistance (frictional resistance) to periodically fluctuate.  
         [0066]    In the case of the driving force transmitting means shown in FIG. 6, and FIG. 7 (sectional view at line C-C in FIG. 6), the groove  61   a  and hole  61   b  are rendered coincidental in rotational phase, which is different from the structural arrangement shown in FIGS. 3 and 4. In the state shown in FIG. 6, the sleeve shaft  31  and drive shaft  81  are both relatively small in slide resistance (frictional resistance), whereas in the state shown in FIG. 7, they are both relatively large in the slide resistance (frictional resistance). In other words, in the case of the structure shown in FIGS. 6 and 7, the periodic fluctuation in slide resistance (frictional resistance) between the shafts  31  and the coupling  61 , which is caused by their rotation, and the periodic fluctuation in slide resistance (frictional resistance) between the drive shaft  81  and the coupling  61 , which is caused by their rotation, become coincidental in phase. Therefore, the amplitude of the periodic fluctuation in the total slide resistance (frictional resistance) of the coupling  61  is the simple sum of the slide resistance (frictional resistance) on the sleeve shaft side and the slide resistance (frictional resistance) on the drive shaft side, that is, virtually twice the slide resistance (frictional resistance) on one side. In other words, the amplitude is quite large. If the change in the amplitude of the periodic fluctuation in the slide resistance (frictional resistance) is as large as the above described one, the change sometimes causes changes in rotational load, which results in an undesirably phenomenon; for example, the change in rotational load causes the driven shaft to irregularity rotate, and/or causes the driving portion on the upstream side of the driving shaft to vibrate (in the case of an image forming apparatus, it is possible that image density irregularity will be caused by the rotational irregularity).  
         [0067]    In comparison, in the case of the structural arrangement shown in FIGS. 3 and 4, the groove  61   a  is differentiated by 90 deg. in rotational phase from the hole  61   b . Therefore, the periodic fluctuation in the slide resistance (frictional resistance) on the sleeve shaft  31  side, which is caused by the rotation, become differentiated by 90 deg. in rotational phase from that on the drive shaft  81  side. Thus, when the slide resistance on one side is large, the slide resistance on the other side is small. Consequently, the overall slide resistance (frictional resistance) involving the coupling  61 , or the sum of the slide resistance on both the sleeve shaft  31  side and drive shaft  81  side, becomes smaller than each of the slide resistance on the sleeve shaft  31  side and the slide resistance on the drive shaft  81  side, preventing the rotational load from significantly fluctuating.  
         [0068]    As described above, differentiating the groove  61   a  of the coupling  61  by 90 deg. in rotational phase from the hole  61   b  of the coupling  61  prevents the rotational load from significantly fluctuating, which in turn prevents such problems as irregular rotation.  
         [0069]    Next, the process through which coupling  61  becomes engaged with the drive shaft  81  as the process cartridge  21  is inserted into the image forming apparatus main assembly will be described.  
         [0070]    Referring to FIG. 9, before the process cartridge  21  is mounted into the apparatus main assembly, the coupling  61  is resting on the sleeve shaft  31 , tilting downward on the drive shaft  81  side. The pin  82  of the drive shaft  81  and the groove  61   a  of the coupling  61  are not in a specific relationship in terms of rotational phase.  
         [0071]    [0071]FIG. 8 shows the state of the coupling  61  and its adjacencies, in which the pin  82  is differentiated by 90 deg. in rotational phase from the groove  61   a . In order to facilitate the engagement between the pin  82  of the drive shaft  81  and the groove  61   a  of the coupling  61 , which are in a random relationship in terms of rotational phase, (not in alignment with each other in terms of the axial direction of the coupling  61 ) as shown in FIG. 8, while aligning the pin  82  and groove  61   a , the coupling  61  is provided with a couple of tapered portions with slanted surfaces  61   e ,  61   f ,  61   g  and  61   h . As the process cartridge  21  is pushed into the apparatus main assembly, the pins  82  of the drive shaft  81  come into contact with the slanted surfaces  61   e ,  61   f ,  61   g  or  61   h . As the process cartridge  21  is pushed further into the apparatus main assembly, the drive shaft  81  or sleeve shaft  31  is forced to rotate by the contact between the slanted surfaces and the pin  82  of the drive shaft  81 . Eventually, the pin  82  and groove  61   a  are aligned in terms of the axial direction of the coupling  61 , and the pin  82  engages into the groove  61   a , ending the engagement between the coupling  61  and the drive shaft  81 .  
         [0072]    In this structure, an electromagnetic clutch (see FIG. 15) is provided between the drive shaft  81  and a mechanical power source. Therefore, the load exerted by the drive shaft  81  during the idling of the apparatus is in a range of 50-100 gf/cm. In comparison, the load exerted by the development sleeve  13   a  and the load exerted by the injection sleeve  14   a  are each in a range of 700-2000 gf/cm. Therefore, the drive shaft  81  side, which is lower in load, rotates. Further, the vertices of the slanted surfaces  61   e ,  61   f ,  61   g  and  61   h  are differentiated by 90 deg. in rotational phase from the groove  61   a . Therefore, the maximum amount of the rotation which the drive shaft  81  must make in order for the pin  82  of the drive shaft  81  to engage into the groove  61   b  is 90 deg.  
         [0073]    Referring to FIG. 8, the coupling  61  is tilted downward on the end drive shaft  81  side. Therefore, if the vertices  61   i  and  61   j  of the tapered portions are rendered the same in height in terms of the axial direction of the coupling  61 , the pins  82  come into contact with the slanted surfaces  61   e  and  61   g , that is, the slanted surfaces on the top side, one for one, making it impossible for the drive shaft  81  to rotate. In order to prevent the coupling  61  from preventing the drive shaft  81  from rotating, the vertices  61   i  and  61   j  of the tapered portions are differentiated in height as shown in FIG. 8. With the provision of this structural arrangement, as the coupling  61  is moved toward the drive shaft  81 , one end of the pin  82  comes into contact with the slanted surface  61   e , causing the drive shaft  81  to rotate. Then, after he drive shaft  81  is rotated by the further advancement of the coupling  61 , the other end of the pin  82  comes in contact with the slanted surface  61   h . Therefore, the aforementioned engagement failure between the pins  82  and groove  61   b  can be avoided.  
         [0074]    Next, the avoidance of the head-on collision between the leading end of the coupling  61  in terms of the cartridge insertion, and the end surface of the drive shaft  81  on the coupling  61  side, will be described.  
         [0075]    Referring to FIG. 9, in this embodiment, the cylindrical portion  61   c  of the coupling  61  is provided to portions different in internal diameter, and therefore, there is a step between the two portions different in internal diameter. The double-dot chain line in the FIG. 9 represents a coupling, the cylindrical portion  61   c  of which is uniform in internal diameter D1 in terms of its axial direction. In this case, the position of a point  61   k ; that is, the position of the intersection between the vertex  61   i  of the tapered portion of the cylindrical portion  61   c  of the coupling  61 , and the internal surface of the cylindrical portion  61   c  o the coupling  61 , is lower than the highest point  81   k  of the end surface  81   a  of the drive shaft  81 , on the coupling  61  side. Therefore, as the process cartridge  21  is inserted into the apparatus main assembly, the leading end  61   i  of the coupling  61  collides with the end surface  81   a  of the drive shaft  81 , on the coupling  61  side. Thus, in this embodiment, in order to prevent the occurrence of this head-on collision between the coupling  61  and drive shaft  81 , the drive shaft  81  side of the cylindrical portion  61   c  of the coupling  61  is rendered greater in internal diameter to raise the position of the inward end  61   k  of the leading end  61   i , or the position of the inward end of the vertex  61   i  of the tapered portion of the coupling  61 . More concretely, the internal diameter of the drive shaft  81  side of the cylindrical portion  61   c  of the coupling  61  is increased enough to create a step with a rise of 1 mm, between the internal surface of the inward side of the cylindrical portion  61   c  and the internal surface of the drive shaft  81  side of the cylindrical portion  61   c . Consequently, the positional relationship between the highest point  81   k  of the end surface  81   a  of the drive shaft  81  and the leading end  61   k  of the coupling  61  in terms of the vertical direction reverses, preventing the occurrence of the aforementioned engagement failure.  
         [0076]    According to an aspect of the present invention, a certain amount of play is provided between the pin  82  and the bottom of the groove  61   a , and also between the pin  32  and the wall of the hole  61   b , in terms of the axial direction of the coupling  61 . In terms of the circumferential direction of the coupling  61 , however, play is unnecessary since the same effects as those described above can be obtained without the provision of play in the circumferential direction of the coupling  61 .  
         [0077]    As described above, even if the above described play in terms of the circumferential direction of the coupling  61  is not provided, the shaft and coupling are allowed to wobble relative to each other as they rotate. Therefore, rotational driving force is smoothly transmitted; rotational driving force is transmitted without causing vibrations. Also in the case of a structure in which play is provided in terms of the circumferential direction, the shaft and coupling are allowed to wobble relative to each other, and therefore, the same effects as those described above are realized, which is obvious.  
         [0078]    Next, referring to FIG. 10, the structure in which play is provided in terms of the circumferential direction will be concretely describe, regarding the shapes and measurements of the components related to the play.  
         [0079]    The groove  61   a  in which the pin  82  of the drive shaft  81  fits has an U-shaped cross section, and its width B1 is in a range of, for example, 3-3.5 mm, whereas the width b1 of the pin  82 , or the counterpart of the groove  61   a , is 2 mm. Therefore, there is a generous amount of play between the pin  82  and the side walls of the groove  61   a  in terms of the circumferential direction.  
         [0080]    FIGS.  11 ( a ) and  11 ( b ) show examples of the shape of the hole  61   b  in which the pin  32  of the sleeve shaft  31  fits. The hole  61   b  is round or rectangular in cross section. The width B2 of the hole  61   b  is in a range of, for example, 3 mm, whereas the width b1 of the pin  32 , or the counterpart of the hole  61   b , is 2 mm. Therefore, there is a generous amount of play between the pin  32  and the wall of the hole  61   b  in terms of the circumferential direction.  
         [0081]    The provision of play in the circumferential direction, on the drive shaft  81  side, allows the unit to be more smoothly inserted into, or removed from, the apparatus main assembly. The provision of play in the circumferential direction, on the sleeve shaft  31  side, makes it easier to put the pin  32  through the hole  61   b  when assembling the driving force transmitting portion, because the provision makes the diameter of the hole  61   b  larger.  
         [0082]    Next, some of the methods for attaching the pins to the shaft will be described.  
         [0083]    As the methods for attaching the pins, there are press-fitting methods and insert-fitting methods. In a press-fitting method, a parallel pin or a spring pin is pressed into a hole of a shaft. In the case of the structure in this embodiment, a press-fitting method is suitable for attaching the pins on the drive shaft  81  side. However, a press-fitting method is not suitable for attaching the pins on the sleeve shaft  31  side, in consideration of the removal of the coupling  61  and the assembly efficiency.  
         [0084]    Next, an insert-fitting method will be described with reference to FIGS.  12 ( a ) and  12 ( b ). FIG. 12( b ) is a plan view of the driving force transmitting portion in FIG. 12( a ).  
         [0085]    The diameter of the pin  32  is 2 mm, whereas the diameter of the hole  31   p  of the sleeve shaft  31  is rendered slightly larger than that of the pin  32 , for example, 2.1 mm. The pin  32  is inserted into the hole  31   p  of the sleeve shaft  31  after the coupling  61  is fitted around the sleeve shaft  31 . Next, in order to prevent the pin  32  from slipping out, a pin retainer  66  is attached to the coupling  61  to cover the hole  61   b  of the coupling  61  with the pin retainer  66 . The pin retainer  66  is held to the coupling  61  with the use of a snap pawl  66   a . Thus, the disengagement of the snap pawl  66   a  allows the pin retainer  66 , pin  32 , and coupling  61 , to be removed in this order.  
         [0086]    Although the above described structural arrangement is for attaching the coupling  61  to the sleeve shaft  31 , the coupling  61  may be attached to the drive shaft  81  to provide the driving force transmitting portion with the same functions and effects as those described above.  
         [0087]    Further, in the above described structural arrangement, the process cartridge  21  comprises the developing device  13 , injection type charging device  14 , and photosensitive drum  11 . However, the structural arrangement for the process cartridge  21  to which the present invention is applicable is not limited to the above described one. In other words, the present invention is applicable to any process cartridge having a single or plurality of drive shafts to be driven.  
         [0088]    Next, referring to FIGS.  16 - 21 , the structural arrangement for fixing the drum cylinder  131  of the photosensitive drum  11  ( 11 C,  11 M,  11 Y and  11 K) to the drum shaft  51 .  
         [0089]    [0089]FIG. 16 is an exploded perspective view of the photosensitive drum  11  and its adjacencies, for showing the structural arrangement for fixing the drum cylinder  131  to the drum shaft  51 , and FIG. 17 is a sectional view of one end of the photosensitive drum  11  and its adjacencies, for showing how the drum cylinder  131  and drum shaft  51  are fixed to each other. FIG. 18 is a sectional view of the drum cylinder and drum shaft, which are in separation, but are coincidental in rotational phase. FIG. 19 is a sectional view of the drum cylinder and drum shaft, at a plane H-H in FIG. 18. FIG. 20 is a side view of the drum cylinder and drum shaft and FIG. 21 is a plan view of the drum cylinder and drum shaft.  
         [0090]    Referring to FIG. 16, a referential code  131  designates a drum cylinder. One end of the drum cylinder  131  is fitted with a drum flange  132 , which is press-fitted into the drum cylinder  131 . A referential code  51  designates a drum shaft, which is provided with a pin  134 . The pin  134  is attached to the drum shaft  51  by press-fitting, and both end portions of the pin  134  project from the peripheral surface of the drum shaft  51  by a predetermined distance.  
         [0091]    The drum flange  132  is provided with a pair of grooves  135  into which the end portions of the above described pin  134  loosely fit. Referring to FIGS. 18 and 19, the bottom end of each groove  135  is tapered in V-shape, constituting a V-shaped tapered portion  136 . This tapered portion  136  is kept pressed upon the pin  134  of the drum shaft  51  by a pressure applying means, which will be described later, to take up the play between the drum flange  132  and drum shaft  51  in terms of their circumferential direction.  
         [0092]    As this time, the means for applying pressure upon the drum cylinder  131  will be described.  
         [0093]    The drum flange  132  is provided with two projections  137 , which are on the front end of the drum flange  132 , projecting inwardly in the radius direction of the drum flange  132 , from the wall of the through hole which extends through the drum flange  132  in the axial direction of the drum flange  132 , whereas the drum shaft  51  is provided with two slots  138 , into which the two projections  137  of the drum flange  132  loosely fit one for one.  
         [0094]    Referring gain to FIG. 16, designated by referential code  139  is a knob, the end portion  139   a  of which is threaded and is screwed into the female threaded hole  133   a  in the drum shaft  51 . A referential code  140  stands for a guiding member, which is rotationally fitted around the knob  139 . The external diameter of the guiding member  140  is rendered slightly smaller than the internal diameter of the drum shaft  51 . Further, the guiding member  140  is provided with two projections  140   a , which engage into the aforementioned slots  138  of the drum shaft  51 . The height of each projection  140   a  of the guiding member  140  is made to be low enough to prevent the projection  140   a  from reaching beyond the peripheral surface of the drum shaft  51 .  
         [0095]    When the projections  137  of the drum flange  132  are in alignment with the slots  138  of the drum shaft  51  in terms of the axial direction of the drum cylinder  131 , the drum shaft  51  is inserted into the drum flange  132  deep enough for the V-shaped tapered portions  136  to come into contact with the pins  134  press-fitted through the drum shaft  51 .  
         [0096]    Next, the knob  139  is put through the guiding member  140 , and the threaded portion  139   a  of the knob  139  is screwed into the female-threaded hole  133   a  of the drum shaft  51 . Prior to this process, the projections  140   a  of the guiding member  140  are aligned with the slots  138  of the drum shaft  51  in the axial direction of the drum cylinder  131 .  
         [0097]    Thus, although the movement of the guiding member  140  in the circumferential direction of the drum cylinder  131  is regulated by the slots  138  of the drum shaft  51 , the guiding member  140  and knob  139  are enabled to freely rotate relative to each other. Therefore, there is nothing to interfere with the screwing of the knob  139  into the drum shaft  51 . As the knob  139  is screwed into the drum shaft  51 , the guiding member  140  is forced to gradually move toward the drum shaft  51 . Eventually, the projections  140   a  of the guiding member  140  come into contact with the projections  137  of the drum flange  132 , and presses the drum flange  132  in the inward direction of the drum shaft  51  in terms of the axial direction of the drum shaft  51 .  
         [0098]    Next, the mechanism for matching the drum flange  132  and drum shaft  51  in rotational phase will be described.  
         [0099]    Referring to FIGS. 18 and 19, the inward end of the drum flange  132  is tapered like a lead cam. As the drum shaft  51  is inserted into the drum flange  132 , the pins  134  projecting from the drum shaft  51  press against the surfaces  141  of the tapered portion, causing the drum flange  132  to rotate until the drum flange  132  and drum shaft  51  are matched in rotational phase, that is, until the pin  134  of the drum shaft  51  align with the grooves  135  of the drum flange  132  in the axial direction of the drum cylinder  131 . When the pin  134  begins to be guided by the grooves  135 , the projections  137  of the drum flange  132  are yet to engage into the slots  138  of the drum shaft  51 , but the drum flange  132  and drum shaft  51  have been matched in rotational phase, making it possible for the drum shaft  51  to be inserted into the drum flange  132 . As the drum shaft  51  is inserted further into the drum flange  132 , the in  134  of the drum shaft  51  comes into contact with the tapered portions  136  of the drum flange  132 .  
         [0100]    Thereafter, the knob  139 , which has been put through the guiding member  140  as described above, is screwed into the female threaded hole  133   a  of the drum shaft  51  to complete the process for fixing the drum flange  132  and drum shaft  51  to each other.  
         [0101]    As is evident from the above description, in this embodiment, the force for pressing the drum flange  132  and drum shaft  51  toward each other, and then keeping them pressed upon each other in terms of the axial direction of the drum cylinder  131 , is transmitted to the drum flange  132  and drum shaft  51  through only the theoretical space occupied by the hypothetical extension of the drum shaft  51 . Therefore, an ordinary bearing, the internal diameter of which is the same as the external diameter of the drum shaft  51  can be used as a bearing  114   a  fitted in an alignment plate  114  for supporting and accurately positioning the drum shaft  51 , outside the drum flange  132 . Further, the drum cylinder  131  and drum shaft  51  can be engaged to each other from outward side of the aligning plate  114 .  
         [0102]    &lt;Embodiment 2&gt; 
         [0103]    Next, referring to FIGS.  22 - 25 , the second embodiment of the present invention will be described. FIG. 22 is a sectional view of the driving force transmitting portion of the second embodiment of the driving force transmitting apparatus in accordance with the present invention, for depicting the structure thereof. In these drawings, the same components and portions as those in FIG. 1 are given the same referential codes as those in FIG. 1, and their descriptions will be omitted.  
         [0104]    In the structure in this embodiment, the drive shaft  81  and sleeve shaft  31  are fitted with couplings  62  and  63 , respectively.  
         [0105]    The coupling  62  is provided with a groove  62   a  and a pair of pawls  62   b  as driving force transmitting portions. Into the groove  62   a , the pin  82  of the drive shaft  81  fits, and the pawls  62   b  engages with the pawls  63   b  of the coupling  63  on the sleeve shaft  31  side to transmit driving force.  
         [0106]    The coupling  62  is provided with a cylindrical portion  62   c , which is fitted around the drive shaft  81  with an eternal diameter of d1, with the provision of a play in their radius direction, being therefore supported by the drive shaft  81 . More specifically, the external diameter d1 of the drive shaft  81  is 8 mm, whereas the internal diameter D1 of the coupling  62  is 8.5 mm.  
         [0107]    The coupling  62  is loosely held to the drive shaft  81  with the use of a pin  82  and an E-shaped retainer ring  84 . The amount of the play δz1 between the pin  82  and the walls of the groove  62   a  is 0.5 mm.  
         [0108]    The provision of play in both the radius and axial directions allows the coupling  62  to pivot about both the axis x perpendicular to the plane of FIG. 22, and the axis y parallel to the vertical direction in the drawing, allowing therefore the coupling  62  and the drive shaft  81  to pivot relative to each other. More specifically, the coupling  62  is allowed to wobble relative to the drive shaft  81 , with the intersection O1 between the axial line of the pin  82  and the axial line of the drive shaft  81  functioning like a fulcrum, as they rotate.  
         [0109]    In this embodiment, the width b1 of the pin  82  and the width B1 of the groove  62   a  are made to be 2 mm and 3 mm, respectively, to provide a certain amount of play between the pin  82  and the walls of the groove  62   a  to improve assembly efficiency as in the first embodiment.  
         [0110]    On the other hand, the coupling  63  on the sleeve shaft  31  side is fitted around the sleeve shaft  31 , with the provision of play between the pin  32  and the walls of the groove  63   a  in both the radius direction of the pin  32  and the axial direction of the sleeve shaft  31 , as is the coupling  62  on the drive shaft  81  side. The external diameter d2 of the sleeve shaft  31  is 8 mm, whereas the internal diameter D2 of the cylindrical portion  63   c  of the coupling  63  is 8.5 mm. The play δz2 between the pin  32  and the walls of the groove  63   a  in the axial direction of the sleeve shaft  31  is 0.5 mm. Therefore, the coupling  63  is allowed to wobble relative to the sleeve shaft  31 , with the intersection O2 between the axial line of the pin  32  and the axial line of the sleeve shaft  31  functioning like a fulcrum.  
         [0111]    With the provision of the above described structural arrangement, the two coupling  62  and  63  are either firmly connected to each other and rotate like a single coupling, or are loosely connected to each other and rotate while being afforded a certain amount of latitude in terms of the alignment between their axial lines. In the former case, the driving force transmitting portion in this embodiment functions like the driving force transmitting portion in the first embodiment (only a coupling  61 ), whereas in the latter case, the driving force transmitting portion in this embodiment is afforded a higher level of latitude in terms of the alignment between their axial lines.  
         [0112]    In either case, when the drive shaft  81  and sleeve shaft  31  are not in alignment with each other, the axial lines of the drive shaft  81  and coupling  62  intersect at the point at which driving force is transmitted (contact point between the pin  32  and the wall of the groove  63   a ), and so do the axial lines of the sleeve shaft  31  and coupling  63 . Therefore, a plurality of the contact points, which are on the same cylindrical plane, and at which driving force is transmitted, become equal in the amount of driving force to be transmitted; driving force is evenly distributed among the plurality of driving force transmission points, as it is transmitted. Consequently, driving force, or torque, is simply transmitted as torque, without being partially turned into unwanted force, or the vibration causing force, as it is transmitted. Therefore, vibrations do not occur. As is evident from the above description, this embodiment can also prevent driving force from being partially turned into the vibration causing force as it is transmitted, preventing therefore the occurrence of the vibration.  
         [0113]    Next, the process in which the couplings  62  and  63  are engaged with each other as the process cartridge  21  is mounted will be described.  
         [0114]    The coupling  63  is structured so that it can be slid toward the sleeve shaft  31  in its axial direction. A spring  33  is a compression spring for exerting rightward pressure upon the coupling  63  as the coupling  63  is moved leftward in FIG. 22. When the coupling  63  is at the normal position as shown in FIG. 22, it is in its natural sate, exerting no pressure upon the coupling  63 . Therefore, the provision of the spring  33  does not eliminates the play δz2, assuring the presence of the play δz2.  
         [0115]    [0115]FIG. 23 is a plan view of the driving force transmitting portion as seen from a plane F-F in the direction indicated by arrow marks. The end surface of the coupling  63  is provided with a pair of pawls  63   b  (FIG. 22 shows only one of the pair of pawls since it is a sectional view). The end surface  63   d  of each pawl  63   d  is flat and is perpendicular to the axial line of the coupling  63 . The driving force transmission surface  63   e  aligns with the axial line of the coupling  63  in terms of the radius direction of the coupling  63 .  
         [0116]    The reason why the pawl  63   b  is given the flat end instead of a pointed one is for preventing the couplings  62  and  63  from improperly engaging with each other (misalignment between the pawls  62   b  and  63   b ). More specifically, when the couplings  62  and  63  are in the proper alignment with each other, the pawls  62   b  of the coupling  62  and the pawls  63   b  of the coupling  63  are alternately positioned in terms of the circumferential direction of the two couplings. However, if the end portions of the pawls  62   b  and  63   b  are pointed, the pawls  62   b  and  63   b  sometimes fail to be alternately positioned in terms of the circumferential direction of the two couplings. This problem occurs when the centers of the couplings  62  and  63  fail to align with each other in terms of the axial direction of the two couplings because of the misalignment between the axial lines of the couplings  62  and  63  and/or the tilting of the couplings  62  and  63  relative to the axial lines of the drive shaft  81  and sleeve shaft  31 , respectively.  
         [0117]    Making the end surface of the pawls  62   b  and  63   b  flat can prevent the aforementioned improper engagement between the couplings  62  and  63 . However, it is likely to cause the ends  62   d  and  63   d  of the pawls  62  and  63 , respectively, to collide head-on with each other. This is why the coupling  63  is enabled to retreat in its axial direction in this embodiment. With the provision of this structural arrangement, as the two couplings collide head-on, the coupling  63  retreats while exerting pressure upon the spring  33 . Then, as the two couplings are made to coincide in rotational phase, by the rotation of the drive shaft  81 , the pawls  62   b  and  63   b  properly engage with each other as the coupling  63  is returned to the normal position by the resiliency of the spring  33 .  
         [0118]    As is evident from the above description, the present invention is also applicable to a drive train in which the two shafts are not allowed to rotate relative to each other.  
         [0119]    The drive train in the first embodiment is an example of a drive train in which the two shafts are allowed to rotate relative to each other. Even if a drive than in which the two shafts are not allowed to rotate relative to each other is provided with only one coupling, the present invention can be embodied by enabling the coupling to slide in its axial direction as described above.  
         [0120]    In this embodiment, the operational effects, which will be described below, can be realized by specifying the shapes (phase) of the components.  
         [0121]    Referring to FIG. 23, the driving force transmission surface  63   e  of the coupling  63 , and the groove  63   a , are differentiated in rotational phase by 45 deg. Further, the couplings  62  and  63  are rendered the same in as many component as possible, so that common components can be used.  
         [0122]    [0122]FIG. 24 is a plan view of the portion of the driving force transmitting portion indicated by a line F-F, as seen from the direction indicated by the arrow marks, and depicts the coupling  63  and sleeve shaft  31 . As shown in FIG. 24, the pin  32  of the sleeve shaft  31  is positioned 45 deg. away from the driving force transmission surface  63   e  of the coupling  63  in the counterclockwise direction.  
         [0123]    [0123]FIG. 25 is a phantom plan view of the couplings  62  and  63  as seen from the portion indicated by a line G-G in FIG. 22, from the direction indicated by the arrow marks, and shows together the two couplings  62  and  63  and two pins  32  and  82 . An arrow mark Q indicates the rotational direction of the driving force transmitting portion. The pin  82  of the drive shaft  81  is positioned 45 deg. apart from the driving force transmission surfaces  62   e  and  63   e  of the two couplings  62  and  63 , respectively, in terms of the clockwise direction. Therefore, the pin  82  of the drive shaft  81  and the pin  32  of the sleeve shaft  31  are differentiated by 90 deg. (45 deg.+45 deg.) in rotational phase (the two pins  82  and  32  are perpendicular to each other).  
         [0124]    Since the pins  32  and  82  are differentiated by 90 deg. in rotational phase (perpendicular to each other), the same mechanism as the above described mechanism in the first embodiment prevents the rotational load from fluctuating. Therefore, problems such as irregular rotation does not occur. Further, in this embodiment, the same functional effects as those realized by the first embodiment can be realized while using the common components for the drive shaft side and sleeve shaft side.  
         [0125]    As described above, in this embodiment, in order to prevent the rotational velocity of the photosensitive member subjected to image exposure, from fluctuating, the sleeve shaft of the photosensitive member is enabled to be accurately connected to the drive shaft on the apparatus main assembly side, to make the rotational centers of the sleeve shaft and drive shaft coincide.  
         [0126]    Further, a slight difference in peripheral velocity between the charge sleeve and development sleeve does not affect image quality. Therefore, the driving force transmitting portion is structured so that driving force can be transmitted from the driving shaft to the driven shaft, which do not coincide with the drive shaft in rotational axis. Therefore, even if the photosensitive, charge sleeve, or development sleeve, is slightly misaligned from the corresponding drive shaft, vibrations do not occur.  
         [0127]    The application of the present invention is not limited to the structural components of an image forming apparatus, which have the above described measurements, materials, shapes, and positional relationship, unless specific notations are provided.  
         [0128]    While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.