Title of Invention: Rotational force transmitting part Abstract: A device for transmitting a rotational force to an electrophotographic photosensitive drum. The device includes a flange connectable with the drum. A coupling member is provided with a rotational force transmitting portion engageable with the flange. Detailed Description: Part general_description_paragraphs: This application is a divisional of co-pending application Ser. No. 11/964,469, filed Dec. 26, 2007. Part FIELD OF THE INVENTION AND RELATED ART: The present invention relates to a rotational force transmitting part for an electrophotographic process cartridge, an electrophotographic image forming apparatus to which the process cartridge is detachably mountable, and an electrophotographic photosensitive drum unit. Examples of the electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (a laser beam printer, an LED printer, and so on), and the like. The process cartridge is prepared by integrally assembling an electrophotographic photosensitive member and process means acting on the electrophotographic photosensitive member into a unit (cartridge) and is mounted to and demounted from a main assembly of the electrophotographic image forming apparatus. For example, the process cartridge is prepared by integrally assembling the electrophotographic photosensitive member and at least one of a developing means, a charging means, and a cleaning means as the process means into a cartridge. Accordingly, examples of the process cartridge include a process cartridge prepared by integrally assembling the electrophotographic photosensitive member and three process means consisting of the developing means, the charging means, and the cleaning means into a cartridge; a process cartridge prepared by integrally assembling the electrophotographic photosensitive member and the charging means as the process means into a cartridge; and a process cartridge prepared by integrally assembling the electrophotographic photosensitive member and two process means consisting of the charging means and the cleaning means. The process cartridge is detachably mountable to an apparatus main assembly by a user by himself (herself). Accordingly, maintenance of the apparatus can be performed by the user by himself without relying on a service person. As a result, operability of the maintenance of the electrophotographic image forming apparatus. In a conventional process cartridge, the following constitution for receiving a rotational driving force, for rotating a drum shaped electrophotographic photosensitive member (hereinafter referred to as a “photosensitive drum”), from an apparatus main assembly is known. On a main assembly side, a rotatable member for transmitting a driving force of a motor and a non circular twisted hole, which is provided at a center portion of the rotatable member and has a cross section integrally rotatable with the rotatable member and provided with a plurality of corners, are provided. On a process cartridge side, a non circular twisted projection, which is provided at one of longitudinal ends of a photosensitive drum and has a cross section provided with a plurality of corners, is provided. When the rotatable member is rotated in an engaged state between the projection and the hole in the case where the process cartridge is mounted to the apparatus main assembly, a rotational force of the rotatable member is transmitted to the photosensitive drum in a state in which an attraction force toward the hole is exerted on the projection. As a result, the rotational force for rotating the photosensitive drum is transmitted from the apparatus main assembly to the photosensitive drum (U.S. Pat. No. 5,903,803). Further, a method in which a photosensitive drum is rotated by engaging a gear fixed to the photosensitive drum constituting a process cartridge has been known (U.S. Pat. No. 4,829,335). However, in the conventional constitution described in U.S. Pat. No. 5,903,803, the rotatable member is required to be moved in a horizontal direction when the process cartridge is mounted to or demounted from the main assembly by being moved in a direction substantially perpendicular to an axial line of the rotatable member. That is, the rotatable member is required to be horizontally moved by an opening and closing operation of a main assembly cover provided to the apparatus main assembly. By the opening operation of the main assembly cover, the hole is moved apart from the projection. On the other hand, by the closing operation of the main assembly cover, the hole is moved toward the projection so as to be engaged with the projection. Accordingly, in the conventional process cartridge, a constitution for moving the rotatable member in a rotational axis direction by the opening and closing operation of the main assembly cover is required to be provided to the main assembly. In the constitution described in U.S. Pat. No. 4,829,335, without moving the driving gear provided to the main assembly along the axial line direction thereof, the cartridge can be mounted to and demounted from the main assembly by being moved in a direction substantially perpendicular to the axial line. However, in this constitution a driving connection portion between the main assembly and the cartridge is an engaging portion between gears, so that it is difficult to prevent rotation non uniformity of the photosensitive drum. Part SUMMARY OF THE INVENTION: A principal object of the present invention is to provide a rotational force transmitting part for a process cartridge, a photosensitive drum unit used in the process cartridge, and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable, capable of solving the above described problems of the conventional process cartridges. Another object of the present invention is to provide a rotational force transmitting part for a process cartridge capable of smoothly rotating a photosensitive drum by being mounted to a main assembly provided with no mechanism for moving a main assembly side coupling member, in its axial line direction, for transmitting a rotational force to the photosensitive drum by an opening and closing operation of a main assembly cover. A further object of the present invention is to provide a photosensitive drum unit used in the process cartridge and an electrophotographic image forming apparatus to which the process cartridge is mountable and from which the process cartridge is demountable. A further object of the present invention is to provide a rotational force transmitting part for a process cartridge demountable from a main assembly of an electrophotographic image forming apparatus provided with a driving shaft in a direction perpendicular to an axial line of the driving shaft. A further object of the present invention is to provide a rotational force transmitting part for a photosensitive drum unit used in the process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable. A further object of the present invention is to provide a rotational force transmitting part for a process cartridge mountable to a main assembly of an electrophotographic image forming apparatus provided with a driving shaft in a direction substantially perpendicular to an axial line of the driving shaft. A further object of the present invention is to provide a rotational force transmitting part for a photosensitive drum unit used in the process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable. A further object of the present invention is to provide a rotational force transmitting part for a process cartridge mountable to and demountable from a main assembly of an electrophotographic image forming apparatus provided with a driving shaft in a direction substantially perpendicular to an axial line of the driving shaft. A further object of the present invention is to provide a rotational force transmitting part for a photosensitive drum unit used in the process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable. A further object of the present invention is to provide a rotational force transmitting part for a process cartridge which compatibly realized that the process cartridge is demountable from a main assembly provided with a driving shaft in a direction substantially perpendicular to an axial line of the driving shaft and is capable of smoothly rotating the photosensitive drum. A further object of the present invention is to provide a rotational force transmitting part for a photosensitive drum unit used in the process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable. A further object of the present invention is to provide a rotational force transmitting part for a process cartridge which compatibly realizes that the process cartridge is mountable to a main assembly provided with a driving shaft in a direction substantially perpendicular to an axial line of the driving shaft and is capable of smoothly rotating the photosensitive drum. A further object of the present invention is to provide a rotational force transmitting part a photosensitive drum unit used in the process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable. A further object of the present invention is to provide a rotational force transmitting part for a process cartridge which compatibly realizes that the process cartridge is mountable to and demountable from a main assembly provided with a driving shaft in a direction substantially perpendicular to an axial line of the driving shaft and is capable of smoothly rotating the photosensitive drum. A further object of the present invention is to provide a rotational force transmitting part for a photosensitive drum unit used in the process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable. According to the present invention, there is provided a rotational force transmitting part for a process cartridge which can be demounted from a main assembly of an electrophotographic image forming apparatus provided with the drive shaft in a direction substantially perpendicular to an axis of a drive shaft. According to the present invention, there is provided a rotational force transmitting part for a photosensitive drum unit usable with the process cartridge and an electrophotographic image forming apparatus to which the process cartridge is detachably mountable. According to the present invention, there is provided a rotational force transmitting part for a process cartridge mountable, in a direction substantially perpendicular to an axis of a drive shaft, to a main assembly of an electrophotographic image forming device provided with the drive shaft. According to the present invention, there is provided a rotational force transmitting part for a photosensitive drum unit usable with the process cartridge and an electrophotographic image forming apparatus with the detachably mountable process cartridge. According to the present invention, there is provided a rotational force transmitting part for a process cartridge which can be mounted and dismounted, in a direction substantially perpendicular to an axis of a drive shaft, to a main assembly of an electrophotographic image forming apparatus provided with the drive shaft. According to the present invention, there is provided a rotational force transmitting part for a photosensitive drum unit usable with the process cartridge and an electrophotographic image forming apparatus relative to which the process cartridge can be mounted and demounted. According to the present invention, a process cartridge is mounted to a main assembly which is not provided with a mechanism for moving a main assembly side drum coupling member for transmitting a rotational force to a photosensitive drum to an axial direction, and can rotate the photosensitive drum smoothly. According to the present invention, a process cartridge can be demounted in a direction substantially perpendicular to an axis of a drive shaft provided in a main assembly, and simultaneously, the smooth rotation of a photosensitive drum can be carried out. According to the present invention, a process cartridge can be mounted in a direction substantially perpendicular to an axis of a drive shaft provided in a main assembly, and simultaneously, the smooth rotation of a photosensitive drum can be carried out. According to the present invention, a process cartridge is mountable and dismountable in a direction substantially perpendicular to an axis of a drive shaft provided in a main assembly, and simultaneously, the smooth rotation of a photosensitive drum can be carried out. These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. Part DESCRIPTION OF THE PREFERRED EMBODIMENTS: The process cartridge and an electrophotographic image forming apparatus according to according to an embodiment of the present invention will be described. Part Embodiment 1: Part (1) Brief Description of Process Cartridge: A process cartridge B to which an embodiment of the present invention is applied will be described with reference to FIGS. 1 to 4. FIG. 1 is a sectional view of the cartridge B. FIGS. 2 and 3 are perspective views of the cartridge B. FIG. 4 is a sectional view of an electrophotographic image forming apparatus main assembly A (hereinafter referred to as an “apparatus main assembly A”). The apparatus main assembly A corresponds to a portion of the electrophotographic image forming apparatus from which the cartridge B is excluded. Referring to FIGS. 1 to 3, the cartridge B includes an electrophotographic photosensitive drum 107. The photosensitive drum 107 is rotated by receiving a rotational force from the apparatus main assembly A by a coupling mechanism when the cartridge B is mounted in the apparatus main assembly A as shown in FIG. 4. The cartridge B is mountable to and demountable from the apparatus main assembly A by a user. A charging roller 108 as a charging means (process means) is provided in contact with an outer peripheral surface of the photosensitive drum 107. The charging roller 108 electrically charges the photosensitive drum 107 by voltage application from the apparatus main assembly A. The charging roller 108 is rotated by the rotation of the photosensitive drum 107. The cartridge B includes a developing roller 110 as a developing means (process means). The developing roller 110 supplies a developer to a developing area of the photosensitive drum 107. The developing roller 110 develops an electrostatic latent image formed on the photosensitive drum 107 with the developer t. The developing roller 110 contains therein a magnet roller (fixed magnet) 111. In contact with a peripheral surface of the developing roller 110, a developing blade 112 is provided. The developing blade 112 defines an amount of the developer t to be deposited on the peripheral surface of the developing roller 110. The developing blade 112 imparts triboelectric charges to the developer t. The developer t contained in a developer accommodating container 114 is sent to a developing chamber 113a by rotation of stirring members 115 and 116, so that the developing roller 110 supplied with a voltage is rotated. As a result, a developer layer to which the electric charges are imparted by the developing blade 112 is formed on the surface of the developing roller 110. The developer t is transferred onto the photosensitive drum 107 depending on the latent image. As a result, the latent image is developed. The developer image formed on the photosensitive drum 107 is transferred onto a recording medium 102 by a transfer roller 104. The recording medium 102 is used for forming an image of the developer thereon and, e.g., is recording paper, label, OHP sheet, and so on. In contact with the outer peripheral surface of the photosensitive drum 107, an elastic cleaning blade 117a as a cleaning means (process means) is disposed. The cleaning blade 117a elastically contacts the photosensitive drum 107 at its end and removes the developer t remaining on the photosensitive drum 107 after the developer image is transferred onto the recording medium 102. The developer t removed from the surface of the photosensitive drum 107 by the cleaning blade 117a is accommodated in a removed developer reservoir 117b. The cartridge B is integrally constituted by a first frame unit 119 and a second frame unit 120. The first frame unit 119 is constituted by a first frame 113 as a part of a cartridge frame B1. The first frame unit 119 includes the developing roller 110, the developing blade 112, the developing chamber 113a, the developer accommodating container 114, and the stirring members 115 and 116. The second frame unit 120 is constituted by a second frame 118 as a part of the cartridge frame B1. The second frame unit 120 includes the photosensitive drum 107, the cleaning blade 117a, the removed developer reservoir 117b, and the charging roller 108. The first frame unit 119 and the second frame unit 120 are rotatably connected with each other by a pin P. By an elastic member 135 (FIG. 3) provided between the first and second frame units 119 and 120, the developing roller 110 is pressed against the photosensitive drum 107. The user attaches (mounts) the cartridge B to a cartridge mounting portion 130a of the apparatus main assembly A by gripping a grip. During the mounting, as described later, a driving shaft 180 (FIG. 17) of the apparatus main assembly A and a coupling member 150 (described later) as a rotational force transmitting part of the cartridge B are connected with each other in synchronism with the mounting operation of the cartridge B. The photosensitive drum 107 or the like is rotated by receiving the rotational force from the apparatus main assembly A. Part (2) Description of Electrophotographic Image Forming Apparatus: With reference to FIG. 4, the electrophotographic image forming apparatus using the above described cartridge B will be described. In the following, a laser beam printer will be described as an example of the apparatus main assembly A. During image formation, the surface of the rotating photosensitive drum 107 is electrically charged uniformly by the charging roller 108. Then, the surface of the photosensitive drum 107 is irradiated with laser light, depending on image information, emitted from an optical means 101 including unshown members such as a laser diode, a polygonal mirror, a lens, and a reflecting mirror. As a result, on the photosensitive drum 107, an electrostatic latent image depending on the image information is formed. The latent image is developed by the above described developing roller 110. On the other hand, in synchronism with the image formation, the recording medium 102 set in a cassette 103a is conveyed to a transfer position by a feeding roller 103b and conveying roller pairs 103c, 103d and 103e. At the transfer position, the transfer roller 104 as a transfer means is disposed. To the transfer roller 104, a voltage is applied. As a result, the developer image formed on the photosensitive drum 107 is transferred onto the recording medium 102. The recording medium 102 onto which the developer image is transferred is conveyed to a fixing means 105 through a guide 103f. The fixing means 105 includes a driving roller 105c and a fixing roller 105b containing therein a heater 105a. To the passing recording medium 102, heat and pressure are applied, so that the developer image is fixed on the recording medium 102. As a result, on the recording medium 102, an image is formed. Thereafter, the recording medium 102 is conveyed by roller pairs 103g and 103h and discharged on a tray 106. The above described roller 103b, the conveying roller pairs 103c, 103d and 103e, the guide 103f, the roller pairs 103g and 103h, and the like constitute a conveying means 103 for conveying the recording medium 102. The cartridge mounting portion 130a is a portion (space) for mounting the cartridge B therein. In a state in which the cartridge B is positioned in the space, the coupling member 150 (described later) of the cartridge B is connected with the driving shaft of the apparatus main assembly A. In this embodiment, the mounting of the cartridge B to the mounting portion 130a is referred to as mounting of the cartridge B to the apparatus main assembly A. Further, demounting (removal) of the cartridge B from the mounting portion 130b is referred to as demounting of the cartridge B from the apparatus main assembly A. Part (3) Description of Constitution of Drum Flange: First, a drum flange at a side where the rotational force is transmitted from the apparatus main assembly A to the photosensitive drum 107 (hereinafter simply referred to a “drive side”) will be described with reference to FIG. 5. FIG. 5(a) is a perspective view of the drum flange at the drive side and FIG. 5(b) is a sectional view of the drum flange taken along S1-S1 line shown in FIG. 5(a). Incidentally, with respect to an axial line direction of the photosensitive drum, a side opposite from the drive side is referred to as a “non-drive side”). A drum flange 151 is formed of a resinous material by ejection molding. Examples of the resinous material may include polyacetal, polycarbonate, and so on A drum shaft 153 is formed of a metallic material such as iron, stainless steel, or the like. Depending on a load torque for rotating the photosensitive drum 107, it is possible to select appropriately the materials for the drum flange 151 and the drum shaft 153. For example, the drum flange 151 may also be formed of the metallic material and the drum shaft 153 may also be formed of the resinous material. When both of the drum flange 151 and the drum shaft 153 are formed of the resinous material, they can be integrally molded. The flange 151 is provided with an engaging portion 151a which engages with an inner surface of the photosensitive drum 107, a gear portion (helical gear or spur gear) 151c for transmitting a rotational force to the developing roller 110, and an engaging portion 151d rotatably supported on a drum bearing. More specifically, as for the flange 151, the engaging portion 151a engages with one end of a cylindrical drum 107a as will be described hereinafter. These are disposed co-axially with a rotation axis L1 of the photosensitive drum 107. And, the drum engaging portion 151a has a cylindrical shape, and a base 151b perpendicular thereto is provided. The base 151b is provided with a drum shaft 153 outwardly projected with respect to the direction of the axis L1. This drum shaft 153 is co-axial with the drum engaging portion 151a. These are fixed so as to be co-axial with the rotation axis L1. As for the fixing method thereof the press-fitting, the bonding, the insert molding, and so on are available, and they are selected properly. The drum shaft 153 comprises the circular column portion 153a which has a projection configuration, and is disposed so as to be co-axially with the rotation axis of the photosensitive drum 107. The drum shaft 153 is provided on the end part of the photosensitive drum 107 on the axis L1 of the photosensitive drum 107. In addition, the drum shaft 153 is about 5-15 mm in diameter in consideration of the material, the load, and the space. A free end portion 153b of the circular column portion 153a has a semi-spherical surface configuration so that it can incline smoothly, when an axis of a drum coupling member 150 which is a rotating force transmitting portion inclines, as will be described in detail hereinafter. In addition, in order to receive the rotational force from the drum coupling member 150, a rotating force transmitting pin (rotating force receiving member (portion) 155 are provided on the photosensitive drum 107 side of the free end of the drum shaft 153. The pin 155 is extended in the direction substantially perpendicular to the axis of the drum shaft 153. The pin 155 as the rotational force receiving member has a cylindrical shape which has a diameter smaller than that of the circular column portion 153a of the drum shaft 153, and is made of the metal or the resin material. And, it is fixed by press-fitting, bonding, and so on to the drum shaft 153. And, the pin 155 is fixed in the direction which the axis thereof intersects the axis L1 of the photosensitive drum 107. Preferably, it is desirable to dispose the axis of the pin 155 so as to pass the center P2 of the spherical surface of the free end portion 153b of the drum shaft 153 (FIG. 5(b)). Although the free end portion 153b is the semi-spherical surface configuration actually, the center P2 is the center of a phantom spherical surface that the semispherical surface makes the part thereof. In addition, the number of the pins 155 can be selected properly. In this embodiment, a single pin 155 is used from the standpoint of the assembling property and in order to transmit driving torque assuredly. The pin 155 passes said center P2, and is through the drum shaft 153. And, the pin 155 is outwardly projected at the positions of the peripheral surface of the drum shaft 153 which are diametrically opposite (155a1, 155a2). More particularly, the pin 155 is projected in the direction perpendicular to the axis (axis L1) of the drum shaft 153 relative to the drum shaft 153 at the two opposite places (155a1, 155a2). By this, the drum shaft 153 receives the rotational force from the drum coupling member 150 at the two places. In this embodiment, the pin 155 is mounted to the drum shaft 153 in the range of 5 mm from the free end of the drum shaft 153. However, this does not limit the present invention. In addition, a space portion 151e formed by the engaging portion 151d and the base 151b receives a part of drum coupling member 150, in mounting the drum coupling member 150 (which will be described hereinafter) to the flange 151. In this embodiment, the gear portion 151a for transmitting the rotational force to the developing roller 110 is mounted to the flange 151. However, the rotation of the developing roller 110 may be transmitted not through the flange 151. In that case, the gear portion 151c is unnecessary. However, in the case of disposing the gear portion 151a at the flange 151, integral molding, with the flange 151, of the gear portion 151a can be utilized. The flange 151, the drum shaft 153, and the pin 155 function as the rotational force receiving member which receives the rotational force from the drum coupling member 150 as will be described hereinafter. Part (4) Structure of Electrophotographic Photosensitive Member Drum Unit: Referring to FIG. 6 and FIG. 7, the structure of an electrophotographic photosensitive member drum unit (“drum unit”) will be described. FIG. 6(a) is a perspective view, as seen from the driving side, of the drum unit U1, and FIG. 6(b) is a perspective view as seen from the non-driving side. In addition, FIG. 7 is a sectional view taken along S2-S2 of FIG. 6(a). The photosensitive drum 107 has a cylindrical drum 107a coated with a photosensitive layer 107b on the peripheral surface. The cylindrical drum 107a has an electroconductive cylinder, such as the aluminum, and the photosensitive layer 107b applied thereon. The opposite ends thereof are provided with the drum surface and the substantially co-axial opening 107a1, 107a2, in order to engage the drum flange (151, 152). More particularly, the drum shaft 153 is provided on the end part of the cylindrical drum 107a co-axially with the cylindrical drum 107a. Designated by 151c is a gear and transmits a rotational force which the coupling 150 received from a drive shaft 180 to a developing roller 110. The gear 151c is integrally molded with the flange 15. The cylinder 107a may be hollow or solid. As to the drum flange 151 of the driving side, since it has been described in the foregoing, the description is omitted. A drum flange 152 of the non-driving side is made of the resin material similarly to the driving side with injection molding. And, a drum engaging portion 152b and a bearing portion 152a are substantially co-axially disposed with each other. In addition, the flange 152 is provided with a drum grounding plate 156. The drum grounding plate 156 is an electroconductive thin plate (metal). The drum grounding plate 156 includes contact portions 156b1, 156b2 which contact the inner surface of the electroconductive cylindrical drum 107a, and a contact portion 156a which contacts the drum grounding shaft 154 (which will be described hereinafter). And, for the purpose of grounding the photosensitive drum 107, the drum grounding plate 156 is electrically connected with the apparatus main assembly A. A drum flange 152 of the non-driving side is made of the resin material, similarly to the driving side with injection molding. And, a drum engaging portion 152b and a bearing portion 152a are substantially co-axially disposed with each other. In addition, the flange 152 is provided with a drum grounding plate 156. The drum grounding plate 156 is an electroconductive thin plate (metal). The drum grounding plate 156 includes contact portions 156b1, 156b2 which contact the inner surface of the electroconductive cylindrical drum 107a, and a contact portion 156a which contacts the drum grounding shaft 154 (which will be described hereinafter). And, for the purpose of grounding the photosensitive drum 107, the drum grounding plate 156 is electrically connected with the apparatus main assembly A. Although it has been described that the drum grounding plate 156 is provided in the flange 152, the present invention is not limited to such an example. For example, the drum grounding plate 156 may be disposed at the drum flange 151, and it is possible to select properly the position which can be connected with the ground. Thus, the drum unit U1 comprises the photosensitive drum 107 which has the cylinder 107a, the flange 151, the flange 152, the drum shaft 153, the pin 155, and the drum grounding plate 156. Part (5) Rotational Force Transmitting Portion (Drum Coupling Member): The description will be made, referring to FIG. 8 as to an example of the drum coupling member which is the rotational force transmitting portion. FIG. 8(a) is a perspective view, as seen from the apparatus main assembly side, of the drum coupling member, FIG. 8(b) is a perspective view, as seen from the photosensitive drum side, of the drum coupling member, and FIG. 8(c) is a view seen in the direction perpendicular to the direction of the coupling rotation shaft L2. In addition, FIG. 8(d) is the side view, as seen from the apparatus main assembly side, of the drum coupling member, FIG. 8(e) is the Figure, as seen from the photosensitive drum side, and FIG. 8(f) is a sectional view taken along S3 in FIG. 8(d). The drum coupling member (“coupling”) 150 engages with a drive shaft 180 (FIG. 17) of the apparatus main assembly A in the state where the cartridge B is mounted set to the installation section 130a. In addition, the coupling 150 is disengaged from the drive shaft 180, when the cartridge B is taken out from the apparatus main assembly A. And, the coupling 150 receives a rotational force from a motor provided in the apparatus main assembly A through the drive shaft 180 in the state where it is engaged with the drive shaft 180. In addition, the coupling 150 transmits the rotational force thereof to the photosensitive drum 107. The materials available for the coupling 150 are the resin materials, such as polyacetal and the polycarbonate PPS. However, in order to raise a rigidity of the coupling 150, the glass fibers, the carbon fibers, and so on may be mixed in the above described resin material correspondingly to a required load torque. In the case of mixing said material, the rigidity of the coupling 150 can be raised. In addition, in the resin material, the metal may be inserted, then the rigidity may further be raised, and the whole coupling may be manufactured from the metal and so on. The coupling 150 mainly comprises three portions. The first portion is engageable with the drive shaft 180 (which will be described hereinafter), and it is a coupling side driven portion 150a for receiving the rotational force from the rotational force transmitting pin 182 which is a rotational force applying portion (main assembly side rotational force transmitting portion) provided on the drive shaft 180. In addition, the second portion is engageable with the pin 155, and it is a coupling side driving portion 150b for transmitting the rotational force to the drum shaft 153. In addition, the third portion is a connecting portion 150c for connecting the driven portion 150a and the driving portion 150b with each other (FIGS. 8(c) and (f)). The driven portion 150a, the driving portion 150b, and the connecting portion 150c may be molded integrally, or, alternatively, the separate parts may be connected with each other. In this embodiment, these are integrally molded with resin material. By this, the manufacturing of the coupling 150 is easy and the accuracy as the parts is high. As shown in FIG. 8(f) the driven portion 150a is provided with a drive shaft insertion opening portion 150m which expands toward the rotation axis L2 of the coupling 150. The driving portion 150b has a drum shaft insertion opening portion 150l. which expands toward the rotation axis L2. The opening 150m has a conical driving shaft receiving surface 150f as an expanded part which expands toward the drive shaft 180 side in the state where the coupling 150 is mounted to the apparatus main assembly A. The receiving surface 150f constitutes a recess 150z as shown in FIG. 8(f). The recess 150z includes the opening 150m at a position opposite the side adjacent the photosensitive drum 107 with respect to the direction of the axis L2. By this, regardless of rotation phase of the photosensitive drum 107 in the cartridge B, the coupling 150 can pivot among a rotational force transmitting angular position, a pre-engagement angular position, and a disengaging angular position relative to the axis L1 of the photosensitive drum 107 without being prevented by the free end portion of the drive shaft 180. The rotational force transmitting angular position, the pre-engagement angular position, and the disengaging angular position will be described hereinafter. A plurality of projections (the engaging portions) 150d1-150d4 are provided at equal intervals on a circumference about the axis L2 on an end surface of the recess 150z. Between the adjacent projections 150d1, 150d2, 150d3, 150d4, the standing-by portions 150k1, 150k2, 150k3, 150k4 are provided. An intervals between the adjacent projections 150d1-150d4 is larger than the outer diameter of the pin 182, so that the rotational force transmitting pins of the drive shaft 180 provided in the apparatus main assembly A (rotational force applying portions) 182 are received. The recesses between the adjacent projections are the standing-by portions 150k1-k4. When the rotational force is transmitted to the coupling 150 from the drive shaft 180, the transmission pins 182a1, 182a2 are received by any of the standing-by portions 150k1-k4. In addition, in FIG. 8(d), the rotational force reception surfaces (rotational force receiving portions) 150e crossing with a rotational direction of the coupling 150 and (150e1-150e4) are provided in the downstream with respect to the clockwise direction (X1) of each projection 150d. More particularly, the projection 150d1 has a receiving surface 150e1, the projection 150d2 has a receiving surface 150e2, the projection 150d3 has a receiving surface 150e3, and, and, a projection 150d4 has a receiving surface 150e4. In the state where the drive shaft 180 rotates, the pin 182a1, 182a2 contacts to any of the receiving surface 150e1-150e4. By doing so, the receiving surface 150e contacted by the pin 182a1, 182a2 is pushed by the pin 182. By this, the coupling 150 rotates about the axis L2. The receiving surface 150e1-150e4 is extended in the direction crossing with the rotational direction of the coupling 150. In order to stabilize the running torque transmitted to the coupling 150 as much as possible, it is desirable to dispose the rotational force receiving surfaces 150e on the same circumference that has the center on the axis L2. By this, the rotational force transmission radius is constant and the running torque transmitted to the coupling 150 is stabilized. In addition, as for the projections 150d1-150d4, it is preferable that the position of the by coupling 150 is stabilized by the balance of the forces which the coupling receives. For that reason, in this embodiment, the receiving surfaces 150e are disposed at the diametrically opposed positions (180 degrees). More particularly, in this embodiment, the receiving surface 150e1 and the receiving surface 150e3 are diametrically opposed relative to each other, and the receiving surface 150e2 and the surface 150e4 are diametrically opposed relative to each other (FIG. 8(d)). By this arrangement, the forces which the coupling 150 receives constitute a force couple. Therefore, the coupling 150 can continue rotary motion only by receiving the force couple. For this reason, the coupling 150 can rotate without the necessity of being specified in the position of the rotation axis L2 thereof. In addition, as for the number thereof, as long as the pins 182 of the drive shaft 180 (the rotational force applying portion) can enter the standing-by portions 150k1-150k2, it is possible to select suitably. In this embodiment, as shown in FIG. 8 the four receiving surfaces are provided. This embodiment is not limited to this example. For example, the receiving surfaces 150e (projections 150d1-150d4) do not need to be disposed on the same circumference (the phantom circle C1 and FIG. 8(d)). Or, it is not necessary to dispose at the diametrically opposed positions. However, the effects described above can be provided by disposing the receiving surfaces 150e as described above. Here, in this embodiment, the diameter of the pin is approximately 2 mm, and a circumferential length of the stand-by portion 150k is approximately 8 mm. The circumferential length of the stand-by portion 150k is an interval between adjacent projections 150d (on the phantom circle). The dimensions are not limiting to the present invention. Similarly to the opening 150m, a drum shaft insertion opening portion 150l has a conical rotational force receiving surface 150i of an as an expanded part which expands toward the drum shaft 153 in the state where it is mounted to the cartridge B. The receiving surface 150i constitutes a recess 150q, as shown in FIG. 8(f). By this, irrespective of the rotation phase of the photosensitive drum 107 in the cartridge B, the coupling 150 can pivot among a rotational force transmitting angular position, a pre-engagement angular position, and a disengaging angular position to the drum axix L1 without being prevented by the free end portion of the drum shaft 153. The recess 150q is constituted in the illustrated example by a conical receiving surface 150i which it has centering on the axis L2. The standby openings 150g1 or 150g2 (“opening”) are provided in the receiving surface 150i (FIG. 8b). As for the coupling 150, the pins 155 can be inserted into the inside of this opening 150g1 or 150g2 so that it may be mounted to the drum shaft 153. And, the size of the openings 150g1 or 150g2 is larger than the outer diameter of the pin 155. By doing so, irrespective of the rotation phase of the photosensitive drum 107 in the cartridge B, the coupling 150 is pivotable among the rotational force transmitting angular position and the pre-engagement angular position (or disengaging angular position) as will be described hereinafter without being prevented by the pin 155. More particularly, the projection 150d is provided adjacent to the free end of the recess 150z. And, the projections (projections) 150d project in the intersection direction crossing with the rotational direction in which the coupling 150 rotates, and are provided with the intervals along the rotational direction. And, in the state where the cartridge B is mounted to the apparatus main assembly A, the receiving surfaces 150e engage to or abutted to the pin 182, and are pushed by the pin 182. By this, the receiving surfaces 150e receive the rotational force from the drive shaft 180. In addition, the receiving surfaces 150e are disposed in equidistant from the axis L2, and constitute a pair interposing the axis L2 they are constituted by the surface in the intersection direction in the projections 150d. In addition, the standing-by portions (recesses) 150k are provided along the rotational direction, and they are depressed in the direction of the axis L2. The standing-by portion 150k is formed as a space between the adjacent projections 150d. In the state where the cartridge B is mounted to the apparatus main assembly A, the pin 182 enters the standing-by portion 150k, and it stands by for being driven. And, when the drive shaft 180 rotates, the pin 182 pushes the receiving surface 150e. By this, the coupling 150 rotates. The rotational force receiving surface (rotational force receiving member (portion)) 150e may be disposed inside of the driving shaft receiving surface 150f. Or, the receiving surface 150e may be provided in the portion outwardly projected from the receiving surface 150f with respect to the direction of the axis L2. When the receiving surface 150e is disposed inside of the receiving surface 150f, the standing-by portion 150k is disposed inside of the receiving surface 150f. More particularly, the standing-by portion 150k is the recess provided between the projections 150d in the inside of the arc part of the receiving surface 150f. In addition, when the receiving surface 150e is disposed at the position which outwardly projects, the standing-by portion 150k is the recess positioned between the projections 150d. Here, the recess may be a through hole extended in the direction of the axis L2, or it may be closed at one end thereof. More particularly, the recess is provided by the space region provided between the projection 150d. And, what is necessary is just to be able to enter the pin 182 into the region in the state where the cartridge B is mounted to the apparatus main assembly A. These structures of the standing-by portion apply similarly to the embodiments as will be described hereinafter. In FIG. 8(e), the rotational force transmission surfaces (the rotational force transmitting portions) 150h and (150h1 or 150h2) are provided in the upstream, with respect to the clockwise direction (X1), of the opening 150g1 or 150g2. And, the rotational force is transmitted to the photosensitive drum 107 from the coupling 150 by the convection sections 150h1 or 150h2 contacting to any of the pins 155a1, 155a2. More particularly, the transmitting surfaces 150h1 or 150h2 push the side surface of the pin 155. By this, the coupling 150 rotates with the center thereof aligned with the axis L2. The transmitting surface 150h1 or 150h2 is extended in the direction crossing with the rotational direction of the coupling 150. Similarly to the projection 150d, it is desirable to dispose the transmitting surfaces 150h1 or 150h2 diametrically opposed relative to each other on the same circumference. At the time of manufacturing the drum coupling member 150 with an injection molding, the connecting portion 150c may become thin. This is because the coupling is manufactured so that the driving force receiving portion 150a, the driving portion 150b and the connecting portion 150c have a substantially uniform thickness. When the rigidity of the connecting portion 150c is insufficient, therefore, it is possible to make the connecting portion 150c thick so that driven portion 150a, the driving portion 150b, and the connecting portion 150c have the substantially equivalent thickness. Part (6) Drum Bearing Member: The description will be made, referring to FIG. 9, about a drum bearing member. FIG. 9(a) is a perspective view, as seen from a drive shaft side, and FIG. 9(b) is a perspective view, as seen from the photosensitive drum side. The drum bearing member 157 rotatably supports the photosensitive drum 107 on the second frame 118. In addition, the bearing member 157 has a function of positioning the second frame unit 120 in the apparatus main assembly A. Further, it has the function of retaining the coupling 150 so that the rotational force can be transmitted to the photosensitive drum 107. As shown in FIG. 9 an engaging portion 157d positioned to the second frame 118 and a peripheral part 157c positioned in the apparatus main assembly A are substantially co-axially disposed. The engaging portion 157d and the peripheral part 157c are annular. And, the coupling 150 is disposed in the space portion 157b inside thereof. The engaging portion 157d and the peripheral part 157c are provided with a rib 157e for retaining the coupling 150 in the cartridge B in the neighborhood of the central portion with respect to the axial direction. The bearing member 157 is provided with holes 157g1 or 157g2 which penetrate the abutment surface 157f and the fixing screw for fixing the bearing member 157 to the second frame 118. As will be described hereinafter, the guide portion 157a for mounting and demounting on and the cartridge B relative to the apparatus main assembly A is integrally provided on the bearing member 157. Part (7) Coupling Mounting Method: Referring to FIG. 10-FIG. 16, the description will be made as to the mounting method of the coupling. FIG. 10(a) is an enlarged view, as seen from the driving side surface, of the major part around the photosensitive drum. FIG. 10(b) is an enlarged view, as seen from the non-driving side surface, of the major part. FIG. 10(c) is a sectional view taken along S4-S4 of FIG. 10(a). FIGS. 11(a) and (b) are an exploded perspective views which illustrate the state before attachment of the primary members of the second frame unit. FIG. 11(c) is a sectional view taken along S5-S5 in FIG. 11(a). FIG. 12 is a sectional view which illustrates a state after attaching. FIG. 13 is a sectional view taken along S6-S6 of FIG. 11(a). FIG. 14 is a sectional view which illustrates a state after rotating the coupling and the photosensitive drum through 90 degrees from the state of FIG. 13. FIG. 15 is a perspective view which illustrates the combined state of the drum shaft and the coupling. FIGS. 15(a1)-(a5) are front views, as seen from the axial direction of the photosensitive drum, and FIGS. 15(b1)-(b5) are perspective views. FIG. 16 is a perspective view which illustrates the state where the coupling is inclined in the process cartridge. As shown in FIG. 15 the coupling 150 is mounted so that the axis L2 thereof can incline in any direction relative to the axis L1 of the drum shaft 153 (coaxial with the photosensitive drum 107). In FIG. 15(a1) and FIG. 15(b1), the axis L2 of the coupling 150 is co-axial with the axis L1 of the drum shaft 153. The state when the coupling 150 is inclined upward from this state is illustrated in FIGS. 15(a2) and (b2). As shown in this Figure, when the coupling 150 is inclined toward the opening 150g side, the opening 150g moves along the pin 155. As a result, the coupling 150 is inclined about an axis AX perpendicular to the axis of the pin 155. In FIGS. 15(a3) and (b3), the state where the coupling 150 is inclined rightward is shown. As shown in this Figure, when the coupling 150 inclines in the orthogonality direction of the opening 150g, the opening 150g rotates about the pin 155. The axis of rotation is the axis line AY of the pin 155. The state where the coupling 150 is inclined downward is shown in FIGS. 15(a4) and (b4), and the state where the coupling 150 is inclined leftward is shown in FIGS. 15(a5) and (b5). The rotation axes AX and AY have been described in the foregoing. In the directions different from the inclining direction described in the foregoing, for example, in the 45-degree direction in FIG. 15(a1) and so on, the inclination is made by combining the rotations in the axes AX and the directions of AY. Thus, the axis L2 can be pivoted in any direction relative to the axis L1. More particularly, the transmitting surface (rotational force transmitting portion) 150h is movable relative to the pin (rotational force receiving portion) 155. The pin 155 has the transmitting surface 150 in the movable condition. And, the transmitting surface 150h and the pin 155 are engaged to each other in the rotational direction of the coupling 150. In this manner, the coupling 150 is mounted to the cartridge. In order to accomplish this, the gap is provided between the transmitting surface 150h and the pin 155. By this, the coupling 150 is pivotable in all directions substantially relative to the axis L1. As described above, the opening 150g is extended in the direction (the rotational axis direction of the coupling 150) crossing with the projection direction of the pins dnewton@example.org. Therefore, as has been described hereinbefore, the coupling 150 is pivotable in all the directions. It has been mentioned that the axis L2 is slantable or inclinable in any direction relative to the axis L1. However, the axis L2 does not necessarily need to be linearly slantable to the predetermined angle in the full range of 360-degree direction in the coupling 150. For example, the opening 150g can be selected to be slightly wider in
{'bibliographic_information': "{'country': 'US', 'doc-number': '13617916', 'kind': 'B2', 'date': '20120914', 'invention_title': 'Rotational force transmitting part'}", 'source_file': './grant/2013/ipg130528.xml', 'source_data': 'USPTO-Grant'}