Image bearing member, process cartridge and image forming apparatus

Abstract: The present invention provides an image bearing member (9) comprising an image bearing layer (9b) capable of bearing an image, a substrate (9a) for supporting the image bearing layer, and a weight portion (9d) arranged with the substrate asymmetrically with respect to a center of said substrate in a generatrix direction thereof.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic device, an electrostatic recording device and the like, a process cartridge mountable to such image forming apparatus, and an image bearing member such as a photosensitive drum, a dielectric drum and the like used with such apparatus. In image forming apparatuses such as copying machines, a latent image is formed by selectively exposing an image bearing member which has been uniformly charged, and the latent image is then visualized with toner as a toner image which is in turn transferred onto a recording sheet, thereby recording an image on the recording sheet. In such apparatuses, whenever the toner is consumed or used up, new toner must be replenished. However, the toner replenishing operation not only is troublesome, but also often causes the contamination of surroundings. Further, the maintenance of various elements must be performed only by an expert service men, which is inconvenience for the user. To avoid this, a so-called process cartridge wherein a photosensitive drum, a charger, a developing device, a cleaning device and the like are integrally contained in a cartridge housing which can be removably mounted to an image forming apparatus, whereby the replenishment of toner or the exchange of parts service lives of which have been expired can be permitted and the maintenance can be facilitated, and an image forming apparatus to which such process cartridge can be mounted have been proposed and put into practical use. As charger devices used with such image forming apparatus such as an electrophotographic device, in general, a corona discharger has been conventionally utilised. However, recently, since a power source of low voltage type has been developed, a charger of contact type having a roller-shaped or blade-shaped conductive member has been used because of low generation of ozone. In such a charger, when an AC voltage is applied to the charger roller, the photosensitive drum and the charger roller are vibrated at a frequency twice as great as the frequency of the applied AC voltage, thereby generating the charging noise. The present invention is concerned with providing an image bearing member, a process cartridge and an image forming apparatus, in which noise such as the charging noise, vibrating noise or the like is reduced. In accordance with a first aspect of the present invention there is provided an electrophotographic image bearing member as set out in claim 1. It will also be apparent that in order to keep the base potential of the image bearing member constant, the image bearing member is electrically earthed by abutting an elastic drum earth against the image bearing member. However, if the drum earth does follow the vibration of the image bearing member sufficiently, it is feared that a weak vibrating noise can be generated due to the vibration between the drum earth and the image bearing member. To avoid this, the contact pressure between the drum earth and the image bearing member can be increased. However, if such contact pressure is too great, the inner surface of the drum is damaged due to the strong abutment between the drum and the drum earth for a long time, with the result that, whenever a contact portion of the drum earth passes through the damaged portion of the drum, poor contact and a vibrating noise will be generated. In order that the present invention may be more readily understood embodiments thereof will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is an elevational sectional view of a copying machine within which a process cartridge according to a preferred embodiment of the present invention is mounted; Fig. 2 is a perspective view of the copying machine in a condition that a tray is opened; Fig. 3 is a perspective view of the copying machine in a condition that a tray is closed; Fig. 4 is an elevational sectional view of the process cartridge; Fig. 5 is a perspective view of the process cartridge; Fig. 6 is a perspective view of the process cartridge in an inverted condition; Fig. 7 is an exploded sectional view of the process cartridge in a condition that an upper frame and a lower frame are separated; Fig. 8 is a perspective view of the lower frame showing an internal structure thereof; Fig. 9 is a perspective view of the upper frame showing an internal structure thereof; Fig. 10 is a longitudinal sectional view of a photosensitive drum of the process cartridge; Fig. 11 is a schematic view for explaining the measurement of the charging noise; Fig. 12 is a graph showing the result of the measurement of the charging noise regarding a position of a filler; Fig. 13 is a perspective view of an earthing contact for the photosensitive drum; Fig. 14 is a perspective view of an earthing contact for the photosensitive drum, according to another embodiment; Fig. 15 is a perspective view showing an embodiment wherein an earthing contact which is not bifurcated is used with the photosensitive drum; Fig. 16 is a sectional view of the non-bifurcated earthing contat used with the photosensitive drum; Fig. 17 is an elevational view showing an attachment structure for a charger roller; Fig. 18A is a perspective view of an exposure shutter, and Fig. 18B is a partial sectional view of the exposure shutter; Fig. 19 is a sectional view showing a non-magnetic toner feeding mechanism having an agitating vane; Fig. 20 is a longitudinal sectional view showing a positional relation between the photosensitive drum and a developing sleeve and a structure for pressurizing the developing sleeve; Fig. 21A is a sectional view taken along the line A - A of Fig. 20, and Fig. 21B is a sectional view taken along the line B - B of Fig. 20; Fig. 22 is a sectional view for explaining the pressurizing force acting on the developing sleeve; Fig. 23 is a perspective view of a squeegee sheet in a condition that an upper edge of the sheet is tortuous; Fig. 24A is a perspective view showing a condition that a both-sided adhesive tape is protruded from a lower end of the squeegee sheet, and Figs. 24B and 24C are views showing a condition that a sticking tool is adhered to the protruded both-sided adhesive tape; Fig. 25A is a perspective view showing a condition that the squeegee sheet is sticked to a curved attachment surface with a lower end portion of the sheet being curved, and Fig. 25B is a perspective view showing a condition that an upper end portion of the squeegee sheet is tensioned by releasing the curvature of the attachment surface; Fig. 26 is a perspective view of a squeegee sheet according to another embodiment wherein a width of the sheet is widened straightly and gradually from both ends to a central portion thereof; Fig. 27 is a perspective view for explaining the formation of the curvature of the squeegee sheet attachment surface by pressing the surface; Fig. 28 is a view showing conditions that a recording medium is being guided by a lower surface of the lower frame; Fig. 29 is a sectional view showing a condition that the photosensitive drum is finally assembled; Fig. 30 is a sectional view showing a condition that a developing blade and a cleaning blade are sticked; Fig. 31 is an exploded view for explaining the assembling of the process cartridge; Fig. 32 is a view for explaining a position of guide members when the photosensitive drum of the process cartridge is assembled; Fig. 33 is a sectional view of a structure wherein drum guides are arranged at ends of blade supporting members; Fig. 34 is a perspective view for explaining the attachment of bearing members for the photosensitive drum and the developing sleeve; Fig. 35 is a sectional view of the photosensitive drum and the developing sleeve with the bearing members attached thereto; Fig. 36 is a perspective view for explaining a cover film and a tear tape; Fig. 37 is a perspective view showing a condition that the tear tape is protruded from a gripper; Fig. 38 is a schematic view showing a condition that the process cartridge is gripped by an operator's hand; Fig. 39A is a flow chart showing the assembling and shipping line for the process cartridge, and Fig. 39B is a flow chart showing the disassembling and cleaning line for the process cartridge; Fig. 40 is a perspective view showing a condition that the process cartridge is being mounted within the image forming apparatus; Fig. 41 is a perspective view showing a condition that another process cartridge is being mounted within the image forming apparatus; Fig. 42 is a perspective view showing the arrangement of three contacts provided on the image forming apparatus; Fig. 43 is a sectional view showing the construction of the three contacts; Fig. 44 is a sectional view for explaining the positioning of the relative position between the lower frame and a lens unit; Fig. 45 is a sectional view for explaining the positioning of the relative position between the lower frame and an original glass support; Fig. 46 is a perspective view showing the attachment positions of positioning pegs; Fig. 47 is a schematic elevational view showing the relation between rotary shafts of the drum and of the sleeve and shaft supporting members therefor, and a transmitting direction of a driving force from a drive gear to a flange gear of the photosensitive drum; Fig. 48 is an exploded perspective view of a developing sleeve according to an embodiment wherein it can easily be slid; Fig. 49 is a schematic elevational view of the developing sleeve of Fig. 48; Fig. 50 is an elevational sectional view showing a condition that the upper frame and the lower frame are released; Fig. 51 is a view showing gears and contacts attached to the photosensitive drum; Fig. 52A is an elevational view a developing sleeve receiving member according to another embodiment, and Fig. 52B is an end view of the receiving member of Fig. 52A; Fig. 53 is an elevational view showing an arrangement wherein the developing blade and the cleaning blade can be attached to the interior of the image forming apparatus by pins; Fig. 54 an elevational view showing a condition that the photosensitive drum is being finally assembled, according to another embodiment; Fig. 55 is an elevational sectional view of bearing members for supporting the photosensitive drum and the developing sleeve, according to another embodiment; Fig. 56 is a schematic view of a transmission mechanism for transmitting a driving force from a drive motor of the image forming apparatus to various elements; Figs. 57 and 58 are perspective views showing a condition that the flange gear of the photosensitive drum and a gear integral with the flange gear are protruded from the lower frame; Fig. 59 is a view showing a gear train for transmitting a driving force from the drive gear of the image forming apparatus to the photosensitive drum and the transfer roller; Figs. 60A and 60B are views showing different drive transmitting mechanisms to developing sleeves, wherein magnetic toner is used and non-magnetic toner is used; Fig. 61 is a view of a developing means having stepped portions looked at from a direction that a photosensitive drum is disposed; Fig. 62 is a view of a developing means having stepped portions looked at from a direction that a photosensitive drum is disposed, according to another embodiment; Fig. 63 is a schematic elevational sectional view of a process cartridge; Fig. 64 is a perspective view of a photosensitive drum protecting cover having stepped portions; Fig. 65 is a perspective view of a photosensitive drum protecting cover having stepped portions, according to another embodiment; Fig. 66 is a schematic elevational sectional view of an image forming apparatus within which a process cartridge is mounted; Fig. 67 is an enlarged side view showing an penetrating angle of a recording sheet into a nip between a photosensitive drum and a transfer roller; and Fig. 68 is a graph showing a relation between a character void level and a total pressure of a transfer roller. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First of all, a process cartridge according to a first embodiment of the present invention, and an image forming apparatus utilizing such a process cartridge will be explained with reference to the accompanying drawings. The Whole Construction of a Process Cartridge and an Image Forming System Mounting the Process Cartridge thereon : First of all, the whole construction of the image forming apparatus will briefly be described. Incidentally, Fig. 1 is an elevational sectional view of a copying machine as an example of the image forming apparatus, within which the process cartridge is mounted, Fig. 2 is a perspective view of the copying machine with a tray opened, Fig. 3 is a perspective view of the copying machine with the tray closed, Fig. 4 is an elevational sectional view of the process cartridge, Fig. 5 is a perspective view of the process cartridge, and Fig. 6 is a perspective view of the process cartridge in an inverted condition. As shown in Fig. 1, the image forming apparatus A operates to optically read image information on an original or document 2 by an original reading means 1. A recording medium rested on a sheet supply tray 3 or manually inserted from the sheet supply tray 3 is fed, by a feeding means 5, to an image forming station of the process cartridge B, where a developer (referred to as "toner" hereinafter) image formed in response to the image information is transferred onto the recording medium 4 by a transfer means 6. Thereafter, the recording medium 4 is sent to a fixing means 7 where the transferred toner image is permanently fixed to the recording medium 4. Then, the recording medium is ejected onto an ejection tray 8. The process cartridge B defining the image forming station operates to uniformly charge a surface of a rotating photosensitive drum (image bearing member) 9 by a charger means 10, then to form a latent image on the photosensitive drum 9 by illuminating a light image read by the reading means 1 on the photosensitive drum by means of an exposure means 11, and then to visualize the latent image as a toner image by a developing means 12. After the toner image is transferred onto the recording medium 4 by the transfer means 6, the residual toner remaining on the photosensitive drum 9 is removed by a cleaning means 13. Incidentally, the process cartridge B is formed as a cartridge unit by housing the photosensitive drum 9 and the like within frames which include a first or upper frame 14 and a second or lower frame 15. Further, in the illustrated embodiment, the frames 14, 15 are made of high impact styrol resin (HIPS), and a thickness of the upper frame 14 is about 2 mm and a thickness of the lower frame 15 is about 2.5 mm. However, material and thickness of the frames are not limited to the above, but may be selected appropriately. Next, various parts of the image forming apparatus A and the process cartridge B mountable within the image forming apparatus will be fully described. Image Forming Apparatus First of all, various parts of the image forming apparatus A will be explained. (Original Reading Means) The original reading means 1 serves to optically read the information written on the original, and, as shown in Fig. 1, includes an original glass support 1a which is disposed at an upper portion of a body 16 of the image forming apparatus and on which the original 2 is to be rested. An original hold-down plate 1b having a sponge layer 1b1 on its inner surface is attached to the original glass support 1a for opening and closing movement. The original glass support 1a and the original hold-down plate lb are mounted on the apparatus body 16 for reciprocal sliding movement in the left and right directions in Fig. 1. On the other hand, a lens unit 1c is disposed below the original glass support 1a at the upper portion of the apparatus body 16 and includes a light source 1c1 and a short focus focusing lens array 1c2 therein. With this arrangement, when the original 2 is rested on the original glass support 1a with an image surface thereof faced downside and the light source 1c1 is activated and the original glass support 1a is slid in the left and right direction in Fig. 1, the photosensitive drum 9 of the process cartridge B is exposed by reflection light from the original 2 via the lens array 1c2. (Recording Medium Feeding Means) The feeding means 5 serves to feed the recording medium 4 rested on the sheet supply tray 3 to the image forming station and to feed the recording medium to the fixing means 7. More particularly, after a plurality of recording media 4 are stacked on the sheet supply tray 3 or a single recording medium 4 is manually inserted on the sheet supply tray 3, and leading end(s) of the recording media or medium are abutted against a nip between a sheet supply roller 5a and a friction pad 5b urged against the roller, when a copy start button A3 is depressed, the sheet supply roller 5a is rotated to separate and feed the recording medium 4 to a pair of regist rollers 5c1, 5c2 which, in turn, feed the recording medium is registration with the image forming operation. After the image forming operation, the recording medium 4 is fed to the fixing means 7 by a convey belt 5d and a guide member 5e, and then is ejected onto the ejection tray 8 by a pair of ejector rollers 5f1, 5f2. (Transfer Means) The transfer means 6 serves to transfer the toner image formed on the photosensitive drum 9 onto the recording medium 4 and, in the illustrated embodiment, as shown in Fig. 1, it comprises a transfer roller 6. More particularly, by urging the recording medium 4 against the photosensitive drum 9 in the process cartridge B mounted within the image forming apparatus by means of the transfer roller 6 provided in the image forming apparatus and by applying to the transfer roller 6 a voltage having the polarity opposite to that of the toner image formed on the photosensitive drum 9, the toner image on the photosensitive drum 9 is transferred onto the recording medium 4. (Fixing Means) The fixing means 7 serves to fix the toner image transferred to the recording medium 4 by applying the voltage to the transfer roller 6 and, as shown in Fig. 1, comprises a heat-resistive fixing film 7e wound around and extending between a driving roller 7a, a heating body 7c held by a holder 7b and a tension plate 7d. Incidentally, the tension plate 7d is biased by a tension spring 7f to apply a tension force to the film 7e. A pressure roller 7g is urged against the heating body 7c with the interposition of the film 7e so that the fixing film 7e is pressurized against the heating body 7c with a predetermined force required to the fixing operation. The heating body 7c is made of heat-resistive material such as alumina and has a heat generating surface comprised of a wire-shaped or plate-shaped members having a width of about 160 µm and a length (dimension perpendicular to a plane of Fig. 1) of about 216 mm and made of Ta 2 N for example arranged on an under surface of the holder 7b made of insulation material or composite material including insulation, and a protection layer made of Ta 2 O for example and covering the heat generating surface. The lower surface of the heating body 7c is flat, and front and rear ends of the heating body are rounded to permit the sliding movement of the fixing film 7e. The fixing film 7e is made of heat-treated polyester and has a thickness of about 9 µm. The film can be rotated in a clockwise direction by the rotation of the driving roller 7a. When the recording medium 4 to which the toner image was transferred passes through between the fixing film 7e and the pressure roller 7g, the toner image is fixed to the recording medium 4 by heat and pressure. Incidentally, in order to escape or discharge the heat generated by the fixing means 7 out of the image forming apparatus, a cooling fan 17 is provided within the body 16 of the image forming apparatus. The fan 17 is rotated, for example when the copy start button A3 (Fig. 2) is depressed, so as to generate air flows a (Fig. 1) flowing into the image forming apparatus from the recording medium supply inlet and flow out from the recording medium ejecting outlet. The various parts including the process cartridge B are cooled by the air flows so that the heat does not remain in the image forming apparatus. (Recording Medium Supply and Ejection Trays) As shown in Figs. 1 to 3, the sheet supply tray 3 and the ejection tray 8 are mounted on shafts 3a, 8a, respectively within the system body 16 for pivotal movements in directions b in Fig. 2, and for pivotal movements around shafts 3b, 8b in directions c in Fig. 2. Locking projections 3c, 8c are formed on free ends of the trays 3, 8 at both sides thereof, respectively. These projections can be fitted into locking recesses 1b2 formed in an upper surface of the original hold-down plate 1b. Thus, as shown in Fig. 3, when the trays 3, 8 are folded inwardly to fit the locking projections 3c, 8c into the corresponding recesses 1b2, the original glass support 1a and the original hold-down plate 1b are prevented from sliding in the left and right directions. As a result, an operator can easily lift the image forming apparatus A via grippers 16a and transport it. (Setting Buttons for Density and the like) Incidentally, setting buttons for setting the density and the like are provided on the image forming apparatus A. Briefly explaining, in Fig. 2, a power switch A1 is provided to turn ON and OFF the image forming apparatus. A density adjusting dial A2 is used to adjust the fundamental density (of the copied image) of the image forming apparatus. The copy start button A3, when depressed, starts the copying operation of the image forming apparatus. A copy clear button A4, when depressed, interrupts the copying operation and clears the various setting conditions (for example, the set density condition). A copy number counter button A5 serves to set the number of copies when depressed. An automatic density setting button A6, when depressed, automatically sets the density in the copying operation. A density setting dial A7 is provided so that the operator can adjust the copy density by rotating this dial at need. Process Cartridge Next, various parts of the process cartridge B which can be mounted within the image forming apparatus A will be explained. The process cartridge B includes an image bearing member and at least one process means. For example, the process means may comprise a charge means for charging a surface of the image bearing member, a developing means for forming a toner image on the image bearing member and/or a cleaning means for removing the residual toner remaining on the image bearing member. As shown in Figs. 1 and 4, in the illustrated embodiment, the process cartridge B is constituted as a cartridge unit which can be removably mounted within the body 16 of the image forming apparatus, by enclosing the charger means 10, the developing means 12 containing the toner (developer) and the cleaning means 13 which are arranged around the photosensitive drum 9 as the image bearing member by a housing comprising the upper and lower frames 14, 15. The charger means 10, exposure means 11 (opening 11a) and toner reservoir 12a of the developing means 12 are disposed within the upper frame 14, and the photosensitive drum 9, developing sleeve 12d of the developing means 12 and cleaning means 13 are disposed within the lower frame 15. Now, the various parts of the process cartridge B will be fully described regarding the charger means 10, exposure means 11, developing means 12 and cleaning means 13 in order. Incidentally, Fig. 7 is a sectional view of the process cartridge with the upper and lower frames separated from each other, Fig. 8 is a perspective view showing the internal construction of the lower frame, and Fig. 9 is a perspective view showing the internal construction of the upper frame. (Photosensitive Drum) In the illustrated embodiment, the photosensitive drum 9 comprises a cylindrical drum core 9a having a thickness of about 1 mm and made of aluminium, and an organic photosensitive layer as an image bearing layer 9b disposed on an outer peripheral surface of the drum core, so that an outer diameter of the photosensitive drum 9 becomes 24 mm. The photosensitive drum 9 is rotated in a direction shown by an arrow in response to the image forming operation, by transmitting a driving force of a drive motor 54 (Fig. 56) of the image forming apparatus to a flange gear 9c (Fig. 8) secured to one end of the photosensitive drum 9. During the image forming operation, when the photosensitive drum 9 is being rotated, the surface of the photosensitive drum 9 is uniformly charged by applying to the charger roller 10 (contacting with the drum 9) a vibrating voltage obtained by overlapping a DC voltage with an AC voltage. In this case, in order to prevent a pitch variation corresponding to frequence of vibrating voltage, the surface of the photosensitive drum 9, the frequency of the AC voltage applied to the charger roller 10 must be increased. However, if the frequency exceeds about 2000 Hz, the photosensitive drum 9 and the charger roller 10 will be vibrated, thus generating the so-called "charging noise". That is to say, when the AC voltage is applied to the charger roller 10, an electrostatic attraction force is generated between the photosensitive drum 9 and the charger roller 10, so that the attraction force becomes maximum at the maximum and minimum values of the AC voltage, thus attracting the charger roller 10 against the photosensitive drum 9 while elastically deforming the charger roller. On the other hand, at an intermediate value of the AC voltage, the attraction force becomes minimum, with the result that the elastical deformation of the charger roller 10 is restored to try to separate the charger roller 10 from the photosensitive drum 9. Consequently, the photosensitive drum 9 and the charger roller 10 are vibrated at the frequency of twice as that of the applied AC voltage. Further, when the charger roller 10 is attracted against the photosensitive drum 9, the rotations of the drum and the roller are braked, thus causing the vibration due to the stick slip, which also results in the charging noise. In order to reduce the vibration of the photosensitive drum 9, in the illustrated embodiment, as shown in Fig. 10 (sectional view of the drum), a rigid or elastic filler as a weight portion 9d is disposed within the photosensitive drum 9. The filler 9d may be made of metal such as aluminium, brass or the like, cement, ceramics such as gypsum, or rubber material such as natural rubber, in consideration of the productivity, workability, effect of weight and cost. The filler 9d has a solid cylindrical shape or a hollow cylindrical shape, and has an outer diameter smaller than an inner diameter of the photosensitive drum 9 by about 100 µm, and is inserted into the drum core 9a. That is to say, a gap between the drum core 9a and the filler 9d is set to have a value of 100 µm at the maximum, and an adhesive (for example, cyanoacrylate resin, epoxy resin or the like) 9e is applied on the outer surface of the filler 9d or on the inner surface of the drum core 9a, and the filler 9d is inserted into the drum core 9a, thus adhering them to each other. Now, the test results performed by the inventors, wherein the relation between the position of the filler 9d and the noise pressure (noise level) was checked by varying the position of the filler 9d in the photosensitive drum 9 will be explained. As shown in Fig. 11, the noise pressure was measured by a microphone M arranged at a distance of 30 cm from the front surface of the process cartridge B disposed in a room having the background noise of 43 dB. As result, as shown in Fig. 12, when the filler having a weight of 80 grams was arranged, at a central position in the longitudinal direction of the photosensitive drum 9, the noise pressure was 54.5 - 54.8 dB. Whereas, when the filler having a weight of 40 grams was arranged at a position offset from the central position toward the flange gear 9c by 30 mm, the noise pressure was minimum. From this result, it was found that it was more effective to arrange the filler 9d in the photosensitive drum 9 offset from the central position toward the flange gear 9c. The reason seems that one end of the photosensitive drum 9 is supported via the flange gear 9c while the other end of the drum 9 is supported by a bearing member 26 having no flange, so that the construction of the photosensitive drum 9 is not symmetrical with respect the central position c in the longitudinal (generatrix) direction of a substrate of the drum. That is, the center of filler 9d is apart from the central position c. Thus, in the illustrated embodiment, as shown in Fig. 10, the filler 9d is arranged in the photosensitive drum 9 offset from the central position c (in the longitudinal direction of the drum) toward the flange gear 9c, i.e., toward the drive transmission mechanism to the photosensitive drum 9. Incidentally, in the illustrated embodiment, a filler 9d comprising a hollow aluminium member having a length L3 of 40 mm and a weight of about 20 - 60 grams, preferably 35 - 45 grams (most preferably about 40 grams) is positioned within the photosensitive drum 9 having a longitudinal length L1 of 257 mm at a position offset from the central position c toward the flange gear 9c by a distance L2 of 9 mm. By arranging the filler 9d within the photosensitive drum 9, the latter can be rotated stably, thus suppressing the vibration due to the rotation of the photosensitive drum 9 in the image forming operation. Therefore, even when the frequency of the AC voltage applied to the charger roller 10 is increased, it is possible to reduce the charging noise. Further, in the illustrated embodiment, as shown in Fig. 10, an earthing contact 18a is contacted with the inner surface of the substrate of photosensitive drum 9 and the other end of the earthing contact is abutted against a drum earth contact pin 35a, thereby electrically earthing the photosensitive drum 9. The earthing contact 18a is arranged at the end of the photosensitive drum opposite to the end adjacent to the flange gear 9c. The earthing contact 18a is made of spring stainless steel, spring bronze phosphate or the like and is attached to the bearing member 26. More particularly, as shown in Fig. 13, the earthing contact comprises a base portion 18a1 having a locking opening 18a2 into which a boss formed on the bearing member 26 can be fitted, and two arm portions 18a3 extending from the base portion 18a1, each arm portion being provided at its free end with a semi-circular projection 18a4 protruding downwardly. When the bearing member 26 is attached to the photosensitive drum 9, the projections 18a4 of the earthing contact 18a are urged against the inner surface of the photosensitive drum 9 by the elastic force of the arm portions 18a3. In this case, since the earthing contact 18a is contacted with the photosensitive drum at plural points (two points), the reliability of the contact is improved, and, since the earthing contact 18a is contacted with the photosensitive drum via the semi-circular projections 18a4, the contact between the earthing contact and the photosensitive drum 9 is stabilized. Incidentally, as shown in Fig. 14, lengths of the arm portions 18a3 of the earthing contact 18a may be different from each other. With this arrangement, since positions where the semi-circular projections 18a4 are contacted with the photosensitive drum 9 are offset from each other in the circumferential direction of the drum, even if there is a crack portion extending in the axial direction in the inner surface of the photosensitive drum 9, both projections 18a4 do not contact with such crack portion simultaneously, thereby maintaining the earthing contact (between the contact and the drum) without fail. Incidentally, when the lengths of the arm portions 18a3 are different, the contacting pressure between one of the arm portions 18a3 and the photosensitive drum is different from the contacting pressure between the other arm portion and the drum. However, such difference can be compensated, for example, by changing the bending angles of the arm portions 18a3. In the illustrated embodiment, while the earthing contact 18a had two arm portions 18a3 as mentioned above, three or more arm portions may be provided, or, when the earthing contact is contacted with the inner surface of the photosensitive drum 9 without fail, a single arm portion 18a3 (not bifurcated) having no projection may be used, as shown in Figs. 15 and 16. Now, if the contacting pressure between the earthing contact 18a and the inner surface of the photosensitive drum 9 is too weak, the semi-circular projections 18a4 cannot follow the unevenness of the inner surface of the photosensitive drum, thus causing the poor contact between the earthing contact and the photosensitive drum and generating the noise due to the vibration of the arm portions 18a3. In order to prevent such poor contact and-noise, the contacting pressure must be increased. However, if the contacting pressure is too strong, when the image forming apparatus is used for a long time, the inner surface of the photosensitive drum will be damaged by the high pressure of the semi-circular projections 18a4. Consequently, when the semi-circular projections 18a4 pass through such damaged portion, the vibration occurs, thus causing the poor contact and the vibration noise. In consideration of the above affairs, it is preferable that the total contacting pressure between the earthing contact 18a and the inner surface of the photosensitive drum is set in a range between about 10 grams and about 200 grams. That is to say, according to the test result effected by the inventors, when the contacting pressure was smaller than about 10 grams, it was feared that the poor contact was likely to occur in response to the rotation of the photosensitive drum, thus causing the radio wave jamming regarding other electronic equipments. On the other hand, when the contacting pressure was greater than about 200 grams, it was feared that the inner surface of the photosensitive drum 9 was damaged due to the sliding contact between the drum inner surface and the earthing contact 18a for a long time, thus causing the abnormal noise and/or poor contact. Incidentally, although the generation of the above noise and the like sometimes cannot be eliminated completely because of the inner surface condition of the photosensitive drum, it is possible to reduce the vibration of the photosensitive drum 9 by arranging the filler 9d within the drum 9, and it is also possible to prevent the damage of the drum and the poor contact more effectively by disposing the conductive grease on the contacting area between the earthing contact 18a and the inner surface of the photosensitive drum 9. Further, since the earthing contact 18a positioned on the bearing member 26 is situated remote from the filler 9d offset toward the flange gear 9c, the earthing contact can easily be attached to the bearing member. (Charger Means) The charger means serves to charge the surface of the photosensitive drum 9. In the illustrated embodiment, the charger means is of so-called contact charging type as disclosed in the Japanese Patent Laid-open Appln. No. 63-149669. More specifically, as shown in Fig. 4, the charger roller 10 is rotatably mounted on the inner surface of the upper frame 14 via a slide bearing 10c. The charger roller 10 comprises a metallic roller shaft 10b (for example, a conductive metal core made of iron, SUS or the like), an elastic rubber layer made of EPDM, NBR or the like and arranged around the roller shaft, and an urethane rubber layer dispersing carbon therein and arranged around the elastic rubber layer, or comprise a metallic roller shaft and a foam urethane rubber layer dispersing carbon therein. The roller shaft 10b of the charger roller 10 is held by bearing slide guide pawls 10d of the upper frame 14 via the slide bearing 10c so that it cannot detached from the upper frame and it can slightly be moved toward the photosensitive drum 9. The roller shaft 10b is biased by a spring 10a so that the charger roller 10 is urged against the surface of the photosensitive drum 9. Thus, the charger means is constituted by the charger roller 10 incorporated into the upper frame 14 via the bearing 10c. In the image forming operation, when the charger roller 10 is driven by the rotation of the photosensitive drum 9, the surface of the photosensitive drum 9 is uniformly charged by applying the overlapped DC and AC voltage to the charger roller 10 as mentioned above. Now, the voltage applied to the charger roller 10 will be described. Although the voltage applied to the charger roller 10 may be the DC voltage alone, in order to achieve the uniform charging, the vibration voltage obtained by overlapping the DC voltage and the AC voltage as mentioned above should be applied to the charger roller. Preferably, the vibration voltage obtained by overlapping the DC voltage having the peak-to-peak voltage value greater, by twice or more, than the charging start voltage when the DC voltage alone is used, and the AC voltage is applied to the charger roller 10 to improve the uniform charging (refer to the Japanese Patent Laid-open Appln. No. 63-149669). The "vibration voltage" described herein means a voltage the voltage value whereof is periodically changed as a function of time and preferably has the peak-to-peak voltage greater, by twice or more, than the charging start voltage when the surface of the photosensitive drum is charged only by the DC voltage. Further, the wave form of the vibration voltage is not limited to the sinusoidal wave, but may be rectangular wave, triangular wave or pulse wave. However, the sinusoidal wave not including the higher harmonic component is preferable in view of the reduction of the charging noise. The DC voltage may include a voltage having the rectnagular wave obtained by periodically turning ON/OFF a DC voltage source, for example. As shown in Fig. 17, the application of the voltage to the charger roller 10 is accomplished by urging one end 18c1 of a charging bias contact 18c against a charging bias contact pin of the image forming apparatus as will be described later, and the other end 18c2 of the charging bias contact 18c is urged against the metallic roller shaft 10b, thereby applying the voltage to the charger roller 10. Incidentally, since the charger roller 10 is biased by the elastic contact 18c toward the right in Fig. 17, the charger roller bearing 10c disposed remote from the contact 18c has a hooked stopper portion 10c1. Further, a stopper portion 10e depending from the upper frame 14 is arranged near the contact 18c in order to prevent the excessive axial movement of the charger roller 10 when the process cartridge B is dropped or vibrated. In the illustrated embodiment, with the arrangement as mentioned above, the voltage of 1.6 - 2.4 KVVpp, - 600 VV DC (sinusoidal wave) is applied to the charger roller 10. When the charger roller 10 is incorporated into the upper frame 14, first of all, the bearing 10c is supported by the guide pawls 10d of the upper frame 14 and then the roller shaft 10b of the charger roller 10 is fitted into the bearing 10c. And, when the upper frame 14 is assembled with the lower frame 15, the charger roller 10 is urged against the photosensitive drum 9, as shown in Fig. 4. Incidentally, the bearing 10c for the charger roller 10 is made of conductive bearing material including a great amount of carbon filler, and the voltage is applied to the charger roller 10 from the charging bias contact 18c via the metallic spring 10a so that the stable charging bias can be supplied. (Exposure Means) The exposure means 11 serves to expose the surface of the photosensitive drum 9 uniformly charged by the charger roller 10 with a light image from the reading means 1. As shown in Figs. 1 and 4, the upper frame 14 is provided with an opening 11a through which the light from the lens array 1c2 of the image forming apparatus is illuminated onto the photosensitive drum 9. Incidentally, when the process cartridge B is removed from the image forming apparatus A, if the photosensitive drum 9 is exposed by the ambient light through the opening 11a, it is feared that the photosensitive drum is deteriorated. To avoid this, a shutter member 11b is attached to the opening 11a so that when the process cartridge B is removed from the image forming apparatus A the opening 11a is closed by the shutter member 11b and when the process cartridge is mounted within the image forming apparatus the shutter member opens the opening 11a. As shown in Figs. 18A and 18B, the shutter member 11b has an L-shaped cross-section having a convex portion directing toward the outside of the cartridge, and is pivotally mounted on the upper frame 14 via pins 11b1. A torsion coil spring 11c is mounted around one of the pins 11b1 so that the shutter member 11b is biased by the coil spring 11c to close opening 11a in a condition that the process cartridge B is dismounted from the image forming apparatus A. As shown in Fig. 18A, abutment portions 11b2 are formed on the outer surface of the shutter member 11b so that, when the process cartridge B is mounted within the image forming apparatus A and an upper opening/closing cover 19 (Fig. 1) openable with respect to the body 16 of the image forming apparatus is closed, a projection 19a formed on the cover 19 is abutted against the abutment portions 11b2, thereby rotating the shutter member 11b in a direction shown by the arrow e (Fig. 18B) to open the opening 11a. In the opening and closing operation of the shutter member 11b, since the shutter member 11b has the L-shaped cross-section and the abutment portions 11b2 are disposed outwardly of the contour of the cartridge B and near the pivot pins 11b1, as shown in Figs. 4 and 18B, the shutter member 11b is abutted against the projection 19a of the cover 19 outwardly of the contour of the process cartridge B. As a result, even when the opening and closing angle of the shutter member 11b is small, a leading end of the rotating shutter member 11b is surely opened, thereby surely illuminating the light from the lens array 1c2 disposed above the shutter member onto the photosensitive drum to form the good electrostatic latent image on the surface of the photosensitive drum 9. By constituting the shutter member 11b as mentioned above, when the process cartridge B is inserted into the image forming apparatus, it is not necessary to retard the cartridge B from the shutter opening projection 19a of the cover 19 of the image forming apparatus, with the result that it is possible to shorten the stroke of the projection, thereby making the process cartridge B and the image forming apparatus A small-sized. (Developing Means) Next, the developing means 12 will be explained. The developing means 12 serves to visualize the electrostatic latent image formed on the photosensitive drum 9 by the exposure means with toner as a toner image. Incidentally, in this image forming apparatus A, although magnetic toner or non-magnetic toner can be used, in the illustrated embodiment, the developing means in the process cartridge B includes the magnetic toner as one-component magnetic developer. Binder resin of the one-component magnetic toner used in the developing operation may be the following or a mixture of the following polymer of styrene and substitute thereof such as polystyrene and polyvinyltoluene; styrene copolymer such as styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styreneacrylic acid ethyl copolymer or styrene-acrylic acid butyl copolymer; polymethylmethacrylate, polybutylmethacrylate, polyvinylacetate, polyethylene, polypropylene, polyvinylbutyral, polyacrylic acid resin, rosin, modified rosin, turpentine resin, phenolic resin, aliphatic hydrocarbon resin, alicyclic hydrocarbon resin, aromatic petroleum resin, paraffin wax, carnauba wax or the like. As for the coloring material added to the magnetic toner it may be known carbon black, copper phthalocyanine, iron black or the like. The magnetic fine particles contained in the magnetic toner may be of the material magnetizable when placed in the magnetic field, such as ferromagnetic powder of metal such as iron, cobalt, and nickel, powder of metal alloy or powder of compound such as magnetite or ferrite. As shown in Fig. 4, the developing means 12 for forming the toner image with the magnetic toner has a toner reservoir 12a for containing the toner, and a toner feed mechanism 12b disposed within the toner reservoir 12a and adapted to feed out the toner. Further, the developing means is so designed that the developing sleeve 12d having a magnet 12c therein is rotated to form a thin toner layer on a surface of the developing sleeve. When the toner layer is being formed on the developing sleeve 12d, the developable frictional charging charges are applied to the electrostatic latent image on the photosensitive drum 9 by the friction between the toner and the developing sleeve 12d. Further, in order to regulate a thickness of the toner layer, a developing blade 12e is urged against the surface of the developing sleeve 12d. The developing sleeve 12d is disposed in a confronting relation to the surface of the photosensitive drum 9 with a gap of about 100 - 400 µm therebetween. As shown in Fig. 4, the magnetic toner feed mechanism 12b has feed members 12b1 made of polypropylene (PP), acrylobutadienestyrol (ABS), high-impact styrol (HIPS) or the like and reciprocally shiftable in a direction shown by the arrows f along a bottom surface of the toner reservoir 12a. Each feed member 12b1 has a substantial triangular cross-section and is provided with a plurality of long rod members extending along the rotation axis of the photosensitive drum (direction perpendicular to the plane of Fig. 4) for scraping the whole bottom surface of the toner reservoir 12a. The rod members are interconnected at their both ends to constitute an integral structure. Further, there are three feed members 12b1, and the shifting range of the feed members are selected to be greater than a bottom width of the triangular cross-section so that all of the toner on the bottom surface of the toner reservoir can be scraped. In addition, an arm member 12b2 is provided at its free end with a projection 12b6, thereby preventing the feed members 12b1 from floating and being disordered. The feed member 12b1 has a lock projection 12b4 at its one longitudinal end, which projection is rotatably fitted into a slot 12b5 formed in the arm member 12b2. The arm member 12b2 is rotatably mounted on the upper frame 14 via a shaft 12b3 and is connected to an arm (not shown) disposed outside the toner reservoir 12a. Further, a drive transmitting means is connected to the feed members 12b1 so that, when the process cartridge B is mounted within the image forming apparatus A, the driving force from the image forming apparatus is transmitted to the feed members to swing the arm member 12b2 around the shaft 12b3 by a predetermined angle. Incidentally, as shown in Fig. 7 and the like, the feed members 12b1 and the arm member 12b2 may be integrally formed from resin such as polypropylene, polyamide or the like so that they can be folded at a connecting portion therebetween. Accordingly, in the image forming operation, when the arm member 12b2 is rocked by the predetermined angle, the feed members 12b1 are reciprocally shifted along the bottom surface of the toner reservoir 12a in directions f between a condition shown by the solid lines and a condition shown by the broken lines. Consequently, the toner situated near the bottom surface of the toner reservoir 12a is fed toward the developing sleeve 12d by the feed members 12b1. In this case, since each feed member 12b1 has the triangular cross-section, the toner is scraped by the feed members and is gently fed along inclined surfaces of the feed members 12b1. Thus, the toner near the developing sleeve 12d is hard to be agitated, and, therefore, the toner layer formed on the surface of the developing sleeve 12d is hard to be deteriorated. Further, as shown in Fig. 4, a lid member 12f of the toner reservoir 12a is provided with a depending member 12f1. A distance between a lower end of the depending member 12f1 and the bottom surface of the toner reservoir is selected so as to be slightly greater than a height of the triangular cross-section of each toner feed member 12b1. Accordingly, the toner feed member 12b1 is reciprocally shifted between the bottom surface of the toner reservoir and the depending member 12f1, with the result that, if the feed member 12b1 tries to float from the bottom surface of the toner reservoir, such floating is limited or regulated, thus preventing the floating of the feed members 12b1. Incidentally, the image forming apparatus A according to the illustrated embodiment can also receive a process cartridge including the non-magnetic toner. In this case, the toner feed mechanism is driven to agitate the non-magentic toner near the developing sleeve 12d. That is to say, when the non-magnetic toner is used, as shown in Fig. 19, an elastic roller 12g rotated in a direction same as that of the developing sleeve 12d feeds the non-magnetic toner fed from the toner reservoir 12a by the toner feed mechanism 12h toward the developing sleeve 12d. In this case, at a nip between the developing sleeve 12d and the elastic roller 12g, the toner on the elastic roller 12g is frictionally charged by the sliding contact between the toner and the developing sleeve 12d to be adhered onto the developing sleeve 12d electrostatically. Thereafter, during the rotation of the developing sleeve 12d, the non-magnetic toner adhered to the developing sleeve 12d enters into an abutment area between the developing blade 12e and the developing sleeve 12d to form the thin toner layer on the developing sleeve, and the toner is frictionally charged by the sliding contact between the toner and the developing sleeve with the polarity sufficiently to develop the electrostatic latent image. However, when the toner remains on the developing sleeve 12d, the remaining toner is mixed with the new toner fed to the developing sleeve 12d and is fed to the abutment area between the developing sleeve and the developing blade 12e. The remaining toner and the new toner are frictionally charged by the sliding contact between the toner and the developing sleeve 12d. In this case, however, although the new toner is charged with the proper charge, since the remaining toner is further charged from the condition that it has already been charged with the proper charge, it is over-charged. The over-charged or excessively charged toner has the adhesion force (to the developing sleeve 12d) stronger than that of the property charged toner, thus becoming harder to use in the developing operation. To avoid this, in the illustrated embodiment, regarding the process cartridge containing the non-magnetic toner, as shown in Fig. 19, the non-magnetic toner feed mechanism 12h comprises a rotary member 12h1 disposed in the toner reservoir 12a, which rotary member 12h1 has an elastic agitating vane 12h2. When the non-magnetic toner cartridge is mounted within the image forming apparatus A, the drive transmitting means is connected to the rotary member 12h1 so that the latter is rotated by the image forming apparatus in the image forming operation. In this way, when the image is formed by using the cartridge containing the non-magnetic toner and mounted within the image forming apparatus, the toner in the toner reservoir 12a is greatly agitated by the agitating vane 12h2. As a result, the toner near the developing sleeve 12d is also agitated to be mixed with the toner in the toner reservoir 12a, thereby dispersing the charging charges removed from the developing sleeve 12d in the toner within the toner reservoir to prevent the deterioration of the toner. By the way, the developing sleeve 12d on which the toner layer is formed is arranged in a confronting relation to the photosensitive drum 9 with a small gap therebetween (about 300 µm regarding the process cartridge containing the magnetic toner, or about 200 µm regarding the process cartridge containing the non-magnetic toner). Accordingly, in the illustrated embodiment, abutment rings each having an outer diameter greater than that of the developing sleeve by an amount corresponding to the small gap are arranged in the vicinity of both axial ends of the developing sleeve 12d and outside the toner layer forming area so that these rings are abutted against the photosensitive drum 9 at zones outside the latent image forming area. Now, the positional relation between the photosensitive drum 9 and the developing sleeve 12d will be explained. Fig. 20 is a longitudinal sectional view showing a positional relation between the photosensitive drum 9 and the developing sleeve 12d and a structure for pressurizing the developing sleeve, Fig. 21A is a sectional view taken along the line A - A of Fig. 20, and Fig. 21B is a sectional view taken along the line B - B of Fig. 20. As shown in Fig. 20, the developing sleeve 12d on which the toner layer is formed is arranged in a confronting relation to the photosensitive drum 9 with the small gap therebetween (about 200 - 300 µm). In this case, the photosensitive drum 9 is rotatably mounted on the lower frame 15 by rotatably supporting a rotary shaft 9f of the flange gear 9c at the one end of the drum via a supporting member 33. The other end of the photosensitive drum 9 is also rotatably mounted on the lower frame 15 via a bearing portion 26a of the bearing member 26 secured to the lower frame. The developing sleeve 12d has the above-mentioned abutment rings 12d1 each having the outer diameter greater than that of the developing sleeve by the amount corresponding to the small gap and arranged in the vicinity of both axial ends of the developing sleeve and outside the toner layer forming area so that these rings are abutted against the photosensitive drum 9 at the zones outside the latent image forming area. Further, the developing sleeve 12d is rotatably supported by sleeve bearings 12i disposed between the abutment rings 12d1 in the vicinity of both axial ends of the developing sleeve and outside the toner layer forming area, which sleeve bearings 12i are mounted on the lower frame 15 in such a manner that they can be slightly shifted in directions shown by the arrow g in Fig. 20. Each sleeve bearing 12i has a rearwardly extending projection around which an urging spring 12j having one end abutted against the lower frame 15 is mounted. Consequently, the developing sleeve 12d is always biased toward the photosensitive drum 9 by these urging springs. With this arrangement, the abutment rings 12d1 are always abutted against the photosensitive drum 9, with the result that the predetermined gap between the developing sleeve 12d and the photosensitive drum 9 is always maintained, thereby transmitting the driving force to the flange gear 9c of the photosensitive drum 9 and a sleeve gear 12k of the developing sleeve 12d meshed with the flange gear 9c. The sleeve gear 12k also constitutes a flange portion of the developing sleeve 12d. That is to say, according to the illustrated embodiment, the sleeve gear 12k and the flange portion are integrally formed from resin material (for example, polyacetylene resin). Further, a metallic pin 12d2 having a small diameter (for example, made of stainless steel) and having one end rotatably supported by the lower frame 15 is press-fitted into and secured to the sleeve gear 12k (flange portion) at its center. This metallic pin 12d2 acts as a rotary shaft at one end of the developing sleeve 12d. According to the illustrated embodiment, since the sleeve gear and the flange portion can be integrally formed from resin, it is possible to facilitate the manufacturing of the developing sleeve and to make the developing sleeve 12d and the process cartridge B light-weighted. Now, the sliding directions of the sleeve bearings 12i will be explained with reference to Fig. 22. First of all, the driving of the developing sleeve 12d will be described. When the driving force is transmitted from the drive source (drive motor 54) of the image forming system to the flange gear 9c and then is transmitted from the flange gear 9c to the sleeve gear 12k, the meshing force between the gears is directed to a direction inclined or offset from a tangential line contacting a meshing pitch circle of the flange gear 9c and a meshing pitch circle of the sleeve gear 12k by a pressure angle (20° in the illustrated embodiment). Thus, the meshing force is directed to a direction shown by the arrow P in Fig. 22 ( ≃ 20°). In this case, if the sleeve bearings 12i are slid in a direction parallel to a line connecting the center of rotation of the photosensitive drum 9 and the center of rotation of the developing sleeve 12d, when the meshing force P is divided into a force component Ps of a horizontal direction parallel with the sliding direction and a force component Ph of a vertical direction perpendicular to the sliding direction, as shown in Fig. 22, the force component of the horizontal direction parallel with the sliding direction is directed away from the photosensitive drum 9. As a result, regarding the driving of the developing sleeve 12d, the distance between the photosensitive drum 9 and the developing sleeve 12d is easily varied in accordance with the meshing force between the flange gear 9c and the sleeve gear 12k, with the result that the toner on the developing sleeve 12d cannot be moved to the photosensitive drum 9 properly, thus worsening the developing ability. To avoid this, in the illustrated embodiment, as shown in Fig. 21A, in consideration of the transmission of the driving force from the flange gear 9c to the sleeve gear 12k, the sliding direction of the sleeve bearing 12i at the driving side (side where the sleeve gear 12k is disposed) is coincided with directions shown by the arrow Q. That is to say, an angle  formed between the direction of the meshing force P (between the flange gear 9c and the sleeve gear 12k) and the sliding direction is set to have a value of about 90° (92° in the illustrated embodiment). With this arrangement, the force component Ps of the horizontal direction parallel with the sliding direction is negligible, and, in the illustrated embodiment, the force component Ps acts to slightly bias the developing sleeve 12d toward the photosensitive drum 9. In such a case, the developing sleeve 12d is pressurized by an amount corresponding to spring pressure α of the urging springs 12j to maintain the distance between the photosensitive drum 9 and the developing sleeve 12d constant, thereby ensuring the proper development. Next, the sliding direction of the slide bearing 12i at the non-driving side (side where the sleeve gear 12k is not arranged) will be explained. At the non-driving side, unlike to the above-mentioned driving side, since the slide bearing 12i does not receive a driving force, as shown in Fig. 21B, the sliding direction of the slide bearing 12i is selected to be substantially parallel with a line connecting a center of the photosensitive drum 9 and a center of the developing sleeve 12d. In this way, when the developing sleeve 12d is pressurized toward the photosensitive drum 9, by changing the urging angle for urging the developing sleeve 12d at the driving side from that at the non-driving side, the positional relation between the developing sleeve 12d and the photosensitive drum 9 is always maintained properly, thus permitting the proper development. Incidentally, the sliding direction of the slide bearing 12i at the driving side may be set to be substantially parallel with the line connecting the center of the photosensitive drum 9 and the center of the developing sleeve 12d as in the case of the non-driving side. That is to say, as described in the above-mentioned embodiment, at the driving side, since the developing sleeve 12d is urged away from the photosensitive drum 9 by the force component Ps (of the meshing force between the flange gear 9c and the sleeve gear 12k) directing toward the sliding direction of the slide bearing 12i, in this embodiment, the urging force of the urging spring 12j at the driving side may be set to have a value greater than that at the non-driving side by an amount corresponding to the force component Ps. That is, when the urging force of the urging spring 12j to the developing sleeve 12d at the non-driving side is P, the urging force P2 of the urging spring 12j at the driving side is set to have a relation P2 = P1 + Ps, with the result that the developing sleeve 12d is always subjected to the proper urging force, thus ensuring the constant distance between the developing sleeve and the photosensitive drum 9. (Cleaning Means) The cleaning means 13 serves to remove the residual toner remaining on the photosensitive drum 9 after the toner image on the photosensitive drum 9 has been transferred to the recording medium 4 by the transfer means 6. As shown in Fig. 4, the cleaning means 13 comprises an elastic cleaning blade 13a contacting with the surface of the photosensitive drum 9 and adapted to remove or scrape off the residual toner remaining on the photosensitive drum 9, a squeegee sheet 13b slightly contacting with the surface of the photosensitive drum 9 and disposed below the cleaning blade 13a to receive the removed toner, and a waste toner reservoir 13c for collecting the waste toner received by the sheet 13b. Incidentally, the squeegee sheet 13b is slightly contacted with the surface of the photosensitive drum 9 and the serves to permit the passing of the residual toner remaining on the photosensitive drum, but to direct the toner removed from the photosensitive drum 9 by the cleaning blade 13a to a direction away from the surface of the photosensitive drum 9. Now, a method for attaching the squeegee sheet 13b will be described. The squeegee sheet 13b is adhered to an attachment surface 13d of the waste toner reservoir 13c via both-side adhesive tape 13e. In this case, the waste toner reservoir 13c is made of resin material (for example, high-impact styrol (HIPS) or the like) and has a slight uneven surface. Thus, as shown in Fig. 23, if the both-sided adhesive tape 13e is merely sticked to the attachment surface 13d and the squeegee sheet 13b is merely attached to the adhesive tape 13e, it is feared that a free edge of the squeegee sheet 13b (to be contacted with the photosensitive drum 9) is tortuous shown by x. If such a tortuous edge x of the squeegee sheet 13b is generated, the squeegee sheet 13b does not closely contact with the surface of the photosensitive drum 9, so that it cannot surely receive the toner removed by the cleaning blade 13a. In order to avoid this, it is considered that, when the squeegee sheet 13b is attached to the attachment surface, as shown in Fig. 24A, the attachment surface 13d at a lower portion of the waste toner reservoir is pulled downwardly by a pulling tool 20 to elastically deform the attachment surface to for a curvature and then the squeegee sheet 13b is sticked to the curved attachment surface, and, thereafter the curvature of the attachment surface is released to apply the tension to the free edge of the squeegee sheet 13b, thereby preventing the free edge from becoming tortuous. However, in the recent small-sized process cartridges B, since the dimension of the attachment surface 13d is small, if the squeegee sheet 13b is sticked to the curved attachment surface 13d, as shown in Fig. 24A, both lower ends or corners 13b1 of the squeegee sheet 13b will be protruded from the attachment surface 13d downwardly. And, when the squeegee sheet 13b is protruded downwardly from the attachment surface 13d, as apparent from the sectional view of Fig. 1, it is feared that the recording medium 4 is interfered with the protruded squeegee sheet 13b. Further, it the squeegee sheet 13b is attached to the curved attachment surface 13d, as shown in Fig. 24A, the both-sided adhesive tape 13e will be protruded from the lower end of the squeegee sheet 13b. Thus, in this condition, when the squeegee sheet 13b is urged against the both-sided adhesive tape 13e by a sticking tool 21, as shown in Fig. 24B, the protruded portion of the both-sided adhesive tape 13e is sticked to the sticking tool 21, with the result that, when the sticking tool 21 is removed, as shown in Fig. 24C, the both-sided adhesive tape 13e is peeled from the attachment surface 13d, thus causing the poor attachment of the squeegee sheet 13b. To avoid this, in the illustrated embodiment, as shown in Fig. 25A, the configuration of the lower end of the squeegee sheet 13b becomes substantially the same as the curvature configuration of the attachment surface 13d which has been curved by the pulling tool 20. That is to say, a width of the squeegee sheet 13b is varied from both longitudinal ends to a central portion so that the latter becomes greater than the former (for example, width at the central portion is about 7.9 mm, and width at both ends is about 7.4 mm). In this way, when the squeegee sheet 13b is attached to the attachment surface, the curved both-sided adhesive tape 13e does not protrude from the squeegee sheet 13b. Further, when the pulling tool 20 is removed to release the curvature of the attachment surface 13d thereby to apply the tension to the upper edge of the squeegee sheet 13b as shown in Fig. 25B, the lower end of the squeegee sheet does not protrude from the attachment surface 13d downwardly. Therefore, the above-mentioned interference between the recording medium 4 and the squeegee sheet 13b and the poor attachment of the squeegee sheet 13b can be prevented. Incidentally, in view of the workability and the service life of a working tool, it is desirable that the lower edge of the squeegee sheet 13b is straight. Thus, as shown in Fig. 26, the width of the squeegee sheet 13b may be varied straightly so that the width at the central portion becomes greater than those at both longitudinal ends in correspondence to the amount of the curvature of the attachment surface 13d. In the above-mentioned embodiment, while the attachment surface 13d was curved by pulling it by the pulling tool 20, it is to be understood that, as shown in Fig. 27, the attachment surface 13d may be curved by pushing toner reservoir partition plates 13c1 integrally formed with the attachment surface 13d by pushing tools 20a. Further, in the illustrated embodiment, while the squeegee sheet attachment surface 13d was formed on the lower portion of the waste toner reservoir 13c, the squeegee sheet 13b may be sticked to a metallic plate attachment surface independently formed from the waste toner reservoir 13c and then metallic plate may be incorporated into the waste toner reservoir 13c. Incidentally, in the illustrated embodiment, the squeegee sheet 13b is made of polyethylene terephthalate (PET) and has a thickness of about 38 µm, a length of about 241.3 mm, a-central width of about 7.9 mm, end widths of about 7.4 mm and an appropriate radius of curvature of about 14556.7 mm. (Upper and Lower Frames) Next, the upper and lower frames 14, 15 constituting the housing of the process cartridge B will be explained. As shown in Figs. 7 and 8, the photosensitive drum 9, the developing sleeve 12d and developing blade 12e of the developing means 12, the cleaning means 13 are provided in the lower frame 15. On the other hand, as shown in Figs. 7 and 9, the charger roller 10, the toner reservoir 12a of the developing means 12 and the toner feed mechanism 12b are provided in the upper frame 14. In order to assemble the upper and lower frames 14, 15 together, four pairs of locking pawls 14a are integrally formed with the upper frame 14 and are spaced apart from each other equidistantly in a longitudinal direction of the upper frame. Similarly, locking openings 15a and locking projections 15b for engaging by the locking pawls 14a are integrally formed on the lower frame 15. Accordingly, when the upper and lower frames 14, 15 are forcibly urged against each other to engage the locking pawls 14a by the corresponding locking openings 15a and locking projections 15b, the upper and lower frames 14, 15 are interconnected. Incidentally, in order to ensure the interconnection between the upper and lower frames, as shown in Fig. 8, a locking pawl 15c and a locking opening 15d are formed near both longitudinal ends of the lower frame 15, respectively, whereas, as shown in Fig. 9, a locking opening 14b (to be engaged by the locking pawl 15c) and a locking pawl 14c (to be engaged by the locking opening 15d) are formed near both longitudinal ends of the upper frame 14, respectively. When the parts constituting the process cartridge B are separately contained within the upper and lower frames 14, 15 as mentioned above, by arranging the parts which should be positioned with respect to the photosensitive drum 9 (for example, developing sleeve 12d, developing blade 12e and cleaning blade 13a) within the same frame (lower frame 15 in the illustrated embodiment), it is possible to ensure the excellent positioning accuracy of each part and to facilitate the assembling of the process cartridge B. Further, as shown in Fig. 8, fitting recesses 15n are formed in the lower frame 15 in the vicinity of one lateral edge thereof. On the other hand, as shown in Fig. 9, fitting projections 14h (to be fitted into the corresponding fitting recesses 15n) are formed on the upper frame 14 in the vicinity of one lateral edge thereof at intermediate locations between the adjacent locking pawls 14a. Further, in the illustrated embodiment, as shown in Fig. 8, fitting projections 15e are formed on the lower frame 15 near two corners thereof, whereas fitting recesses 15f are formed in the lower frame near the other two corners. On the other hand, as shown in Fig. 9, fitting recesses 14d (to be engaged by the corresponding fitting projections 15e) are formed in the upper frame 14 near two conrers thereof, whereas fitting projections 14e (to be fitted into the corresponding fitting recesses 15f) are formed in the lower frame near the other two corners. Accordingly, when the upper and lower frames 14, 15 are interconnected, by fitting the fitting projections 14h, 14e, 15e (of the upper and lower frames 14, 15) into the corresponding fitting recesses 15n, 15f, 14d, the upper and lower frames 14, 15 are firmly interconnected to each other so that, even if a torsion force is applied to the interconnected upper and lower frames 14, 15, they are not disassembled. Incidentally, the positions of the above-mentioned fitting projections and fitting recesses may be changed so long as the interconnected upper and lower frames 14, 15 are not disassembled by any torsion force applied thereto. Further, as shown in Fig. 9, a protection cover 22 is rotatably mounted on the upper frame 14 via pivot pins 22a. The protection cover 22 is biased toward a direction shown by the arrow h in Fig. 9 by torsion coil springs (not shown) arranged around the pivot pins 22a, so that the projection cover 22 closes or covers the photosensitive drum 9 in the condition that the process cartridge B is removed from the image forming apparatus A as shown in Fig. 4. More specifically, as shown in Fig. 1, the photosensitive drum 9 is so designed that it is exposed from an opening 15g formed in the lower frame 15 to be opposed to the transfer roller 6 in order to permit the transferring of the toner image from the photosensitive drum onto the recording medium 4. However, in the condition that the process cartridge B is removed from the image forming apparatus A, if the photosensitive drum 9 is exposed to the atmosphere, it will be deteriorated by the ambient light and the dirt and the like will be adhered to the photosensitive drum 9. To avoid this, when the process cartridge B is dismounted from the image forming apparatus A, the opening 15g is closed by the protection cover 22, thereby protecting the photosensitive drum 9 from the ambient light and dirt. Incidentally, when the process cartridge B is mounted within the image forming apparatus A, the protection cover 22 is rotated by a rocking mechanism (not shown) to expose the photosensitive drum 9 from the opening 15g. Further, as apparent from Fig. 1, in the illustrated embodiment, the lower surface of the lower frame 15 also acts as a guide for conveying the recording medium 4. The lower surface of the lower frame is formed as both side guide portions 15h1 and a stepped central guide portion 15h2 (Fig. 6). The longitudinal length (i.e., distance between the steps) of the central guide portion 15h2 is about 102 - 120 mm (107 mm in the illustrated embodiment) which is slightly greater than a width (about 100 mm), and the depth of the step is selected to have a value of about 0.8 - 2 mm. With this arrangement, the central guide portion 15h2 increases the conveying space for the recording medium 4, with the result that, even when thicker and resilient sheet such as a post card, visiting card or envelope is used as the recording medium 4, such thicker sheet does not interfere with the guide surface of the lower frame 15, thereby preventing the recording medium from jamming. On the other hand, when a thin sheet having a greater width than that of the post card such as a plain sheet is used as the recording medium, since such sheet (recording medium) is guided by the both side guide portions 15h1, it is possible to convey the sheet without floating. Now, the lower surface of the lower frame 15 acting as the convey guide for the recording medium will be described more concretely. As shown in Fig. 28, the both side guide portions 15h1 can be flexed by an amount La (= 5 - 7 mm) with respect to a tangential direction X regarding a nip N between the photosensitive drum 9 and the transfer roller 6. Since the both side guide portions 15h1 are formed on the lower surface of the lower frame 15 designed to provide the required space between the lower frame and the developing sleeve 12d and the required space for sufficiently supplying the toner to the developing sleeve, such guide portions are determined by the position of the developing sleeve 12d selected to obtain the optimum developing condition. If the lower surfaces of the side guide portions are approached to the tangential line X, the thickness of the lower portion of the lower frame 15 is decreased, thus causing a problem regarding the strength of the process cartridge B. Further, the position of a lower end 13f of the cleaning means 13 is determined by the positions of the cleaning blade 13a, the squeegee sheet 13b and the like constituting the cleaning means 13 as described later, and is so selected to provide a distance Lb (= 3 - 5 mm) preventing the interference with the recording medium 4 being fed. Incidentally, in the illustrated embodiment, as angle β between a vertical line passing through the rotational center of the photosensitive drum 9 shown in Fig. 28 and a line connecting the rotational center of the photosensitive drum and the rotational center of the transfer roller 6 is selected to have a value of 5 - 20 degrees. In consideration of the above affairs, by providing the recess or step having a depth Lc (= 1 - 2 mm) only in the central guide portion 15h2 to approach this guide portion to the tangential line X, it is possible to feed the thicker and resilient recording medium 4 smoothly without reducing the strength of the lower frame 15. Incidentally, in most cases, since the thicker and resilient recording medium 4 is the visiting card, envelope or the like which is narrower than the post card under the general specification of the image forming system, so long as the width of the stepped or recessed central guide portion 15h2 is selected to be slightly greater than that of the post card, there is no problem in the practical use. Further, regulating projections 15i protruding downwardly are formed on the outer surface of the lower frame 15 in areas outside of the recording medium guiding zone. The regulating projections 15i each protrudes from the guide surface of the lower frame for the recording medium 4 by about 1 mm. With this arrangement, even if the process cartridge B is slightly lowered for some reason during the image forming operation, since the regulating projections 15i are abutted against a lower guide member 23 (Fig. 1) of the body 16 of the image forming system, the further lowering of the process cartridge can be prevented. Accordingly, a space of at least 1 mm is maintained between the lower guide member 23 and the lower guide surface of the lower frame 15 to provide a convey path for the recording medium 4, thereby conveying the recording medium without jamming. Further, as shown in Fig. 1, a recess 15j is formed in the lower surface of the lower frame 15 not to interfere with the regist roller 5c2. Thus, when the process cartridge B is mounted within the image forming apparatus A, since it can be mounted near the regist roller 5c2, the whole image forming apparatus can be small-sized. (Assembling of Process Cartridge) Next, the assembling of the process cartridge having the above-mentioned construction will be explained. In Fig. 29, toner leak preventing seals S having a regular shape and made of Moltopren (flexible polyurethane, manufactured by INOAC Incorp.) rubber for preventing the leakage of toner are sticked on ends of the developing means 12 and of the cleaning means 13 and on the lower frame 15. Incidentally, the toner leak preventing seals S each may not have the regular shape. Alternatively, toner leak preventing seals may be attached by forming recesses in portions (to be attached) of the seals and by pouring liquid material which becomes elastomer when solidified into the recesses. A blade support member 12e1 to which the developing sleeve 12e is attached and a blade support member 13a1 to which the cleaning blade 13a is attached are attached to the lower frame 15 by pins 24a, 24b, respectively. According to the illustrated embodiment, as shown by the phantom lines in Fig. 29, the attachment surfaces of the blade support members 12e1, 13a1 may be substantially parallel to each other so that the pins 24a, 24b can be driven from the same direction. Thus, when a large number of process cartridges B are manufactured, the developing blades 12e and the cleaning blades 13a can be continuously attached by the pins by using an automatic device. Further, the assembling ability for the blades 12e, 13a can be improved by providing a space for a screw driver, and the shape of a mold can be simplified by aligning the housing removing direction from the mold, thereby achieving the cost-down. Incidentally, the developing blade 12e and the cleaning blade 13a may not be attached by the pins (screws), but may be attached to the lower frame 15 by adhesives 24c, 24d as shown in Fig. 30. Also in this case, when the adhesives can be applied from the same direction, the attachment of the developing blade 12e and the cleaning blade 13a can be automatically and continuously performed by using an automatic device. After the blades 12e, 13a have been attached as mentioned above, the developing sleeve 12d is attached to the lower frame 15. Then, the photosensitive drum 9 is attached to the lower frame 15. To this end, in the illustrated embodiment, guide members 25a, 25b are attached to surfaces (opposed to the photosensitive drum) of the blade support members 12e1, 13a1, respectively, at zones outside of the longitudinal image forming area C (Fig. 32) of the photosensitive drum 9. (Incidentally, in the illustrated embodiment, the guide members 25a, 25b are integrally formed with the lower frame 15). A distance between the guide members 25a and 25b is set to be greater than the outer diameter D of the photosensitive drum 9. Thus, after the various parts such as the developing blade 12e, cleaning blade 13a and the like have been attached to the lower frame 15, as shown in Fig. 31, the photosensitive drum 9 can be finally attached to the lower frame while guiding the both longitudinal ends (outside of the image forming area) of the photosensitive drum by the guide members 25a, 25b. That is to say, the photosensitive drum 9 is attached to the lower frame 15 while slightly flexing the cleaning blade 13a and/or slightly retarding and rotating the developing sleeve 12d. If the photosensitive drum 9 is firstly attached to the lower frame 15 and then the blades 12e, 13a and the like are attached to the lower frame, it is feared that the surface of the photosensitive drum 9 is damaged during the attachment of the blades 12e, 13a and the like. Further, during the assembling operation, it is difficult or impossible to check the attachment positions of the developing blade 12e and the cleaning blade 13a and to measure the contacting pressures between the blades and the photosensitive drum. In addition, although lubricant must be applied to the blades 12e, 13a to prevent the increase in torque and/or the blade turn-up due to the close contact between the initial blades 12e, 13a (at the non-toner condition) and the photosensitive drum 9 and the developing sleeve 12d before the blades 12e, 13a are attached to the lower frame 15, such lubricant is likely to be dropped off from the blades during the assembling of the blades. However, according to the illustrated embodiment, since the photosensitive drum 9 is finally attached to the lower frame, the above-mentioned drawbacks and problems can be eliminated. As mentioned above, according to the illustrated embodiment, it is possible to check the attachment positions of the developing means 12 and the cleaning means 13 in the condition that these means 12, 13 are attached to the frames, and to prevent the image forming area of the photosensitive drum from being damaged or scratched during the assembling of the drum. Further, since it is possible to apply the lublicant to the blades in the condition that these means 12, 13 are attached to the frames, the dropping of the lubricant can be prevented, thereby preventing the occurrence of the increase in torque and/or the blade turn-up due to the close contact between the developing blade 12e and the developing sleeve 12d, and the cleaning blade 13a and the photosensitive drum 9. Incidentally, in the illustrated embodiment, while the guide members 25a, 25b were integrally formed with the lower frame 15, as shown in Fig. 33, projections 12e2, 13a2 may be integrally formed on the blade support members 12e1, 13a1 or other guide members may be attached to the blade support members at both longitudinal end zones of the blade support members outside of the image forming area of the photosensitive drum 9, so that the photosensitive drum 9 is guided by these projections or other guide members during the assembling of the drum. After the developing sleeve 12d, developing blade 12e, cleaning blade 13a and photosensitive drum 9 have been attached to the lower frame 15 as mentioned above, as shown in Fig. 34 (perspective view) and Fig. 35 (sectional view), the bearing member 26 is incorporated to rotatably support one ends of the photosensitive drum 9 and of the developing sleeve 12d. The bearing member 26 is made of anti-wear material such as polyacetal and comprises a drum bearing portion 26a to be fitted on the photosensitived rum 9, a sleeve bearing portion 26b to be fitted on the outer surface of the developing sleeve 12d, and a D-cut hole portion 26c to be fitted on an end of a D-cut magnet 12c. Alternatively, the sleeve bearing portion 26b may be fitted on the outer surface of the sleeve bearing 12i supporting the outer surface of the developing sleeve 12d or may be fitted between slide surfaces of the lower frame 15 which are fitted on the outer surface of the slide bearing 12i. Accordingly, when the drum bearing portion 26a is fitted on the end of the photosensitive drum 9 and the end of the magnet 12c is inserted into the D-cut hole portion 26c and the developing sleeve 12d is inserted between into the sleeve bearing portion 26b and the bearing member 26 is fitted into the side of the lower frame 15 while sliding it in the longitudinal direction of the drum, the photosensitive drum 9 and the developing sleeve 12d are rotatably supported. Incidentally, as shown in Fig. 34, the earthing contact 18a is attached to the bearing member 26, and, when the bearing member 26 is fitted into the side of the lower frame, the earthing contact 18a is contacted with the aluminium drum core 9a of the photosensitive drum 9 (see Fig. 10). Further, the developing bias contact 18b is also attached to the bearing member 26, and, when the bearing member 26 is attached to the developing sleeve 12d, the bias contact 18b is contacted with a conductive member 18d contacting the inner surface of the developing sleeve 12d. In this way, by rotatably supporting the photosensitive drum 9 and the developing sleeve 12d by the single bearing member 26, it is possible to improve the positional accuracy of the elements 9, 12d, and to reduce the number of parts, thereby facilitating the assembling operation and achieving the cost-down. Further, since the positioning of the photosensitive drum 9 and the positioning of the developing sleeve 12d and the magnet 12c can be performed by using the single member, it is possible to determine the positional relation between the photosensitive drum 9 and the magnet 12c with high accuracy, with the result that it is possible to maintain a magnetic force regarding the surface of the photosensitive drum 9 constant, thus obtaining the high quality image. In addition, since the earthing contact 18a for earthing the photosensitive drum 9 and the developing bias contact 18b for applying the developing bias to the developing sleeve 12d are attached to the bearing member 26, the compactness of the parts can be achieved effectively, thus making the process cartridge B small-sized effectively. Further, by providing (on the bearing member 26) supported portions for positioning the process cartridge B within the image forming apparatus when the process cartridge is mounted within the image forming apparatus, the positioning of the process cartridge B with regard to the image forming apparatus can be effected accurately. Furthermore, as apparent from Figs. 5 and 6, an outwardly protruding U-shaped projection, i.,e, drum shaft portion 26d (Fig. 20) is also formed on the bearing member 26. When the process cartridge B is mounted within the body 16 of the image forming apparatus, the drum shaft portion 26d is supported by a shaft support member 34 as will be described later, thereby positioning the process cartridge B. In this way, since the process cartridge B is positioned by the bearing member 26 for directly supporting the photosensitive drum 9 when the cartridge is mounted within the apparatus body 16, the photosensitive drum 9 can be accurately positioned regardless of the manufacturing and/or assembling errors of other parts. Further, as shown in Fig. 35, the other end of the magnet 12c is received in an inner cavity formed in the sleeve gear 12k, and an outer diameter of the magnet 12c is so selected as to be slightly smaller than an inner diameter of the cavity. Thus, at the sleeve gear 12k, the magnet 12c is held in the cavity with any play and is maintained in a lower position in the cavity by its own weight or is biased toward the blade support member 12e1 made of magnetic metal such as ZINKOTE (zinc plated steel plate, manufactured by shin Nippon Steel Incorp.) by a magnetic force of the magnet 12c. In this way, since the sleeve gear 12k and the magnet 12c are associated with each other with some play, the friction torque between the magnet 12c and the rotating sleeve gear 12k can be reduced, thereby reducing the torque regarding the process cartridge. On the other hand, as shown in Fig. 31, the charger roller 10 is rotatably mounted within the upper frame 14, and the shutter member 11b, the protection cover 22 and the toner feed mechanism 12b are also attached to the upper frame 15. The opening 12a1 for feeding out the toner from the toner reservoir 12a to the developing sleeve 12d is closed by a cover film 28 (Fig. 36) having a tear tape 27. Further, the lid member 12f is secured to the upper frame, and, thereafter, the toner is supplied to the toner reservoir 12a through the filling opening 12a3 and then the filling opening 12a3 is closed by the lid 12a2, thus sealing the toner reservoir 12a. Incidentally, as shown in Fig. 36, the tear tape 27 of the cover film 28 sticked around the opening 12a1 extends from one longitudinal end (right end in Fig. 36) of the opening 12a1 to the other longitudinal end (left end in Fig. 36) and is bent at the other end and further extends along a gripper portion 14f formed on the upper frame 14 and protrudes therefrom outwardly. Next, the process cartridge B is assembled by interconnecting the upper and lower frames 14, 15 via the above-mentioned locking pawls and locking openings or recesses. In this case, as shown in Fig. 37, the tear tape 27 is exposed between the gripper portion 14f of the upper frame 14 and a gripper portion 15k of the lower frame 15. Therefore, when a new process cartridge B is used, the operator pulls a protruded portion of the tear tape 27 exposed between the gripper portions 14f, 15k to peel the tear tape 27 from the cover film 28 so as to open the opening 12a1, thus permitting the movement of the toner in the toner reservoir 12a toward the developing sleeve 12d. Thereafter, the process cartridge is mounted within the image forming system A. As mentioned above, by exposing the tear tape 27 between the gripper portions 14f, 15k of the upper and lower frames 14, 15, the tear tape 27 can easily be exposed from the process cartridge in assembling the upper and lower frames 14, 15. The gripper portions 14f, 15k are utilized when the process cartridge B is mounted within the image forming apparatus. Thus, if the operator forgets to remove the tear tape 27 before the process cartridge is mounted within the image forming apparatus, since he must grip the gripper portions in mounting the process cartridge, he will know the existence of the non-removed tear tape 27. Further, when the color of the tear tape 27 is clearly different from the color of the frames 14, 15 (for example, if the frames are black, a white or yellow tear tape 27 is used), the noticeability is improved, thus reducing the missing of the removal of the tear tape. Further, for example, when a U-shaped guide rib for temporarily holding the tear tape 27 is provided on the gripper portion 14f of the upper frame 14, it is possible to surely and easily expose the tear tape 27 at a predetermined position during the interconnection between the upper and lower frames 14, 15. Incidentally, when the process cartridge B is assembled by interconnecting the upper and lower frames 14, 15, since the recess 15j for receiving the regist roller 5c2 is formed in the outer surface of the lower frame 15, as shown in Fig. 38, the operator can surely grip the process cartridge B by inserting his fingers into the recess 15j. Further, in the illustrated embodiment, as shown in Fig. 6, slip preventing ribs 14i are formed on the process cartridge B so that the operator can easily grip the process cartridge by hooking his fingers against the ribs. Incidentally, since the recess for receiving (preventing the contact with) the regist roller 5c2 is formed in the lower frame 15 of the process cartridge B, it is possible to make the image forming system more small-sized. Further, as shown in Fig. 6 since the recess 15j is formed along and in the vicinity of the locking pawls 14a and the locking openings 15b through which the upper and lower frames 14, 15 are interconnected, when the operator grips the process cartridge B by hooking his fingers against the recess 15j, the gripping force from the operator acts toward the locking direction, thus surely interlocking the locking pawls 14a and the locking openings 15b. Now, the assembling and shipping line for the process cartridge B will be explained with reference to Fig. 39A. As shown, the various parts are assembled in the lower frame 15, and then, the lower frame into which the various parts are incorporated is checked (for example, the positional relation between the photosensitive drum 9 and the developing sleeve 12d is checked). Then, the lower frame 15 is interconnected to the upper frame 14 within which the parts such as the charger roller 10 are assembled, thereby forming the process cartridge B. Thereafter, the total check of the process cartridge B is effected, and then the process cartridge is shipped. Thus, the assembling and shipping line is very simple. (Mounting of Cartridge) Next, the construction for mounting the process cartridge B within the image forming apparatus A will be explained. As shown in Fig. 40, a loading member 29 having a fitting window 29a matched to the contour of the process cartridge B is provided on the upper opening/closing cover 19 of the image forming apparatus A. The process cartridge B is inserted into the image forming apparatus through the fitting window 29a by gripping the gripper portions 14f, 15k. In this case, a guide ridge 31 formed on the process cartridge B is guided by a guide groove (not numbered) formed in the cover 19 and the lower portion of the process cartridge is guided a guide plate 32 having a hook at its free end. Incidentally, as shown in Fig. 40, a mis-mount preventing projection 30 is formed on the process cartridge B and the fitting window 29a has a recess 29b for receiving the projection 30. As shown in Figs. 40 and 41, the configuration or position of the projection 30 is different depending upon a particular process cartridge containing the toner having the developing sensitivity suitable to a particular image forming apparatus A (i.e. different for each process cartridge), so that, even when a process cartridge containing the toner having the different developing sensitivity is tired to be mounted within the particular image forming apparatus, since the projection 30 does not match with the fitting window 29a of that image forming apparatus, it cannot be mounted within that image forming system. Accordingly, the mis-mounting of the process cartridge B can be prevented, thus preventing the formation of the obscure image due to the different developing sensitive toner. Incidentally, it is also possible to prevent the mis-mounting of a process cartridge including a different kind of photosensitive drum, as well as the different developing sensitivity. Further, since the recess 29b and the projection 30 are situated this side when the process cartridge is mounted, if the operator tries to erroneously mount the process cartridge within the image forming apparatus, he can easily ascertain with his eyes the fact that the projection 30 is blocked by the fitting member 29. Thus, the possibility that the operator forcibly push the process cartridge into the image forming apparatus to damage the process cartridge B and/or the image forming apparatus A as in the conventional case can be avoided. After the process cartridge B is inserted into the fitting window 29a of the opening/closing cover 19, when the cover 19 is closed, the rotaty shaft 9f of the photosensitive drum 9 which is protruded from one side of the upper and lower frames 14, 15 is supported by a shaft support member 33 (Fig. 40) via a bearing 46a, and the rotary shaft 12d2 of the developing sleeve 12d which is protruded from one side of the upper and lower frames 14, 15 is supported by the shaft support member 33 via a slide bearing 46b and a bearing 46c (Fig. 35). On the other hand, the drum shaft portion 26d (Fig. 35) of the bearing member 26 attached to the other end of the photosensitive drum 9 is supported by a shaft support member 34 shown in Fig. 42. In this case, the protection cover 22 is rotated to expose the photosensitive drum 9, with the result that the photosensitive drum 9 is contacted with the transfer roller 6 of the image forming apparatus A. Further, the drum earthing contact 18a contacting the photosensitive drum 9, the developing bias contact 18b contacting the developing sleeve 12d and the charging bias contact 18c contacting the charger roller 10 are provided on the process cartridge B so that these contacts protrude from the lower surface of the lower frame 15, and these contacts 18a, 18b, 18c are urgingly contacted with the drum earthing contact pin 35a, developing bias contact pin 35b and charging bias contact pin 35c (Fig. 42), respectively. As shown in Fig. 42, these contact pins 35a, 35b, 35c are arranged so that the drum earthing contact pin 35a and the charging bias contact pin 35c are disposed at a downstream side of the transfer roller 6 in the recording medium feeding direction and the developing bias contact pin 35b is disposed at an upstream side of the transfer roller 6 in the recording medium feeding direction. Accordingly, as shown in Fig. 43, the contacts 18a, 18b, 18c provided on the process cartridge B are similarly arranged so that the drum earthing contact 18a and the charging bias contact 18c are disposed at a downstream side of the photosensitive drum 9 in the recording medium feeding direction and the developing bias contact 18b is disposed at an upstream side of the photosensitive drum 9 in the recording medium feeding direction. Now, the disposition of the electric contacts of the process cartridge B will be explained with reference to Fig. 51. Incidentally, Fig. 51 is a schematic plan view showing the positional relation between the photosensitive drum 9 and the electric contacts 18a, 18b, 18c. As shown in Fig. 51, the contacts 18a, 18b, 18c are disposed at the end of the photosensitive drum 9 opposite to the end where the flange gear 9c is arranged in the longitudinal direction of the drum. The developing bias contact 18b is disposed at one side of the photosensitive drum 9 (i.e. side where the developing means 12 is arranged), and the drum earthing contact 18a and the charging bias contact 18c are disposed at the other side of the photosensitive drum (where the cleaning means 13 is arranged). The drum earthing contact 18a and the charging bias contact 18c are substantially arranged on a straight line. Further, the developing bias contact 18b is arranged slightly outwardly of the positions of the drum earthing contact 18a and the charging bias contact 18c in the longitudinal direction of the photosensitive drum 9. The drum earthing contact 18a, the developing bias contact 18b and the charging bias contact 18c are spaced apart from the outer peripheral surface of the photosensitive drum 9 gradually in order (i.e. a distance between the contact 18a and the drum is smallest, and a distance between the contact 18c and the drum is greatest). Further, an area of the developing bias contact 18b is greater than an area of the drum earthing contact 18a and an area of the charging bias contact 18c. Furthermore, the developing bias contact 18b, the drum earthing contact 18a and the charging bias contact 18c are disposed outwardly of a position where the arm portions 18a3 of the drum earthing contact 18a are contacted with the inner surface of the photosensitive drum 9, in the longitudinal direction of the photosensitive drum 9. As mentioned above, by arranging the electric contacts between the process cartridge (which can be mounted within the image forming apparatus) and the image forming apparatus at the positioning and abutting side of the process cartridge, it is possible to improve the positional accuracy between the contacts of the process cartridge and the contact pins of the image forming apparatus, thereby preventing the poor electrical connection, and, by arranging the contacts at the non-driving side of the process cartridge, it is possible to make the configurations of the contact pins of the image forming apparatus simple and small-sized. Further, since the contacts of the process cartridge are disposed inside of the contour of the frames of the process cartridge, it is possible to prevent foreign matters from adhering to the contacts, and, thus, to prevent the corrosion of the contacts; and, further to prevent the deformation of the contacts due to the external force. Further, since the developing bias contact 18b is arranged at the side of the developing means 12 and the drum earthing contact 18a and the charging bias contact 18c are arranged at the side of the cleaning means 13, the arrangement of electrodes in the process cartridge can be simplified, thus making the process cartridge small-sized. Now, dimensions of various parts in the illustrated embodiment will be listed up herein below. However, it should be noted that these dimensions are merely an example, and the present invention is not limited to this example: (1) Distance (X1) between the photosensitive drum 9 and the drum earthing contact 18a about 6.0 mm; (2) Distance (X2) between the photosensitive drum 9 and the charging bias contact 18c about 18.9 mm; (3) Distance (X3) between the photosensitive drum 9 and the developing bias contact 18b about 13.5 mm; (4) Width (Y1) of the charging bias contact 18c about 4.9 mm; (5) Length (Y2) of the charging bias contact 18c about 6.5 mm; (6) Width (Y3) of the drum earthing contact 18a about 5.2 mm; (7) Length (Y4) of the drum earthing contact 18a about 5.0 mm; (8) Width (Y5) of the developing bias contact 18a about 7.2 mm; (9) Length (Y6) of the developing bias contact 18a about 8.0 mm (10) Diameter (Z1) of the flange gear 9c about 28.6 mm; (11) Diameter (Z2) of the gear 9i about 26.1 mm; (12) Width (Z3) of the flange gear 9c about 6.7 mm; (13) Width (Z3) of the gear 9i about 4.3 mm; (14) Number of teeth of the flange gear 9c 33; and (15) Number of teeth of the gear 9i 30. Now, the flange gear 9c and the gear 9i will be explained. The gears 9c, 9i comprise helical gears. When the driving force is transmitted from the image forming apparatus to the flange gear 9c, the photosensitive drum 9 mounted in the lower frame 15 with play is subjected to the thrust force to be shifted toward the flange gear 9c, thereby positioning the drum at the side of the lower frame 15. The gear 9c is used with a process cartridge containing the magnetic toner for forming a black image. When the black image forming cartridge is mounted within the image forming apparatus, the gear 9c is meshed with a gear of the image forming apparatus to receive the driving force for rotating the photosensitive drum 9 and is meshed with a gear of the developing sleeve 12d to rotate the latter. The gear 9i is meshed with a gear connected to the transfer roller 6 of the image forming apparatus to rotate the transfer roller. In this case, the rotational load does not almost act on the transfer roller 6. Incidentally, the gear 9i is used with a color image forming cartridge containing the non-magnetic toner. When the color image forming cartridge is mounted within the image forming apparatus, the gear 9c is meshed with the gear of the image forming apparatus to receive the driving force for rotating the photosensitive drum 9. On the other hand, the gear 9i is meshed with the gear connected to the transfer roller 6 of the image forming apparatus to rotate the transfer roller and is meshed with the gear of the developing sleeve 12d for the non-magnetic toner to rotate the latter. The flange gear 9c has a diameter greater than that of the gear 9i, a width greater than that of the gear 9i and a number of teeth greater than that of the gear 9i. Thus, even when the greater load is applied to the gear 9c, the gear 9c can receive the driving force to rotate the photosensitive drum 9 more surely, and can transmit the greater driving force to the developing sleeve 12d for the magnetic toner to rotate the latter more surely. Incidentally, as shown in Fig. 43, each of the contact pins 35a - 35c is held in a corresponding holder cover 36 in such a manner that it can be shifted in the holder cover but cannot be detached from the holder cover. Each contact pin 35a - 35c is electrically connected to a wiring pattern printed on an electric substrate 37 to which the holder covers 36 are attached, via a corresponding conductive compression spring 38. Incidentally, the charging bias contact 18c to be abutted against the contact pin 35c has the arcuated curvature in the vicinity of the pivot axis 19b of the upper opening/closing cover 19 so that, the opening/closing cover 19 mounting the process cartridge B thereon is rotated around the pivot axis 19b in a direction shown by the arrow R to close the cover, the charging bias contact 18c nearest to the pivot axis 19b (i.e. having the minimum stroke) can contact with the contact pin 35c effectively. (Positioning) When the process cartridge B is mounted and the opening/closing cover 19 is closed, the positioning is established so that a distance between the photosensitive drum 9 and the lens unit 1c and a distance between the photosensitive drum 9 and the original glass support 1a are kept constant. Such positioning will now be explained. In shown in Fig. 8, positioning projections 15m are formed on the lower frame 15 to which the photosensitive drum 9 is attached, in the vicinity of both longitudinal ends of the frame. As shown in Fig. 5, when the upper and lower frames 14, 15 are interconnected, these projections 15m protrude upwardly through holes 14g formed in the upper frame 14. Further, as shown in Fig. 44, the lens unit 1c containing therein the lens array 1c2 for reading the original 2 is attached to the upper opening/closing cover 19 (on which the process cartridge B is mounted) via a pivot pin 1c3 for slight pivotal movement around the pivot pin and is biased downwardly (Fig. 44) by an urging spring 39. Thus, when the process cartridge B is mounted on the upper cover 19 and the latter is closed, as shown in Fig. 44, the lower surface of the lens unit 1c is abutted against the positioning projections 15m of the process cartridge B. As a result, when the process cartridge B is mounted within the image forming apparatus A, the distance between the lens array 1c2 in the lens unit 1c and the photosensitive drum 9 mounted on the lower frame 15 is accurately determined, so that the light image optically read from the original 2 can be accurately illuminated onto the photosensitive drum 9 via the lens array 1c2. Further, as shown in Fig. 45, positioning pegs 40 are provided in the lens unit 1c, which positioning pegs can be protruded slightly from the upper cover 19 upwardly through holes 19c formed in the upper cover. As shown in Fig. 46, the positioning pegs 40 are protruded slightly at both longitudinal sides of an original reading slit Z (Figs. 1 and 46). Thus, when the process cartridge B is mounted on the upper cover 19 and the latter is closed and then the image forming operation is started, as mentioned above, since the lower surface of the lens unit 1c is abutted against the positioning projections 15m, the original glass support 1a is shifted while riding on the positioning pegs 40. As a result, a distance between the original 2 rested on the original glass support 1a and the photosensitive drum 9 mounted on the lower frame 15 is always kept constant, thus illuminating the light reflected from the original 2 onto the photosensitive drum 9 accurately. Therefore, since the information written on the original 2 can be optically read accurately and the exposure to the photosensitive drum 9 can be effected accurately, it is possible to obtain the high quality image. (Drive Transmission) Next, the driving force transmission to the photosensitive drum 9 in the process cartridge B mounted within the image forming apparatus A will be explained. When the process cartridge B is mounted within the image forming apparatus A, the rotary shaft 9f of the photosensitive drum 9 is supported by the shaft support member 33 of the image forming apparatus as mentioned above. As shown in Fig. 47, the shaft support member 33 comprises a supporting portion 33a for the drum rotary shaft 9f, and an abutment portion 33b for the rotary shaft 12d2 of the developing sleeve 12d. An overlap portion 33c having a predetermined overhanging amount L (1.8 mm in the illustrated embodiment) is formed on the supporting portion 33a, thus preventing the drum rotary shaft 9f from floating upwardly. Further, when the drum rotary shaft 9f is supported by the supporting portion 33a, the rotary shaft 12d2 of the developing sleeve is abutted against the abutment portion 33b, thus preventing the rotary shaft 12d2 from dropping downwardly. Further, when the upper opening/closing cover 19 is closed, positioning projections 15p of the lower frame 15 protruding from the upper frame 14 of the process cartridge B are abutted against an abutment portion 19c of the opening/closing cover 19. Accordingly, when the driving force is transmitted to the flange gear 9c of the photosensitive drum 9 by driving the drive gear 41 of the image forming apparatus meshed with the flange gear, the process cartridge B is subjected to a reaction force tending to rotate the process cartridge around the drum rotary shaft 9f in a direction shown by the arrow i in Fig. 47. However, since the rotary shaft 12d2 of the developing sleeve is abutted against the abutment portion 33b and the positioning projections 15p of the lower frame 15 protruding from the upper frame 14 are abutted against the abutment portion 19c of the upper cover, the rotation of the process cartridge B is prevented. As mentioned above, although the lower surface of the lower frame 15 acts as the guide for the recording medium 4, since the lower frame is positioned by abutting it against the body of the image forming system as mentioned above, the positional relation between the photosensitive drum 9, the transfer roller 6 and the guide portions 15h1, 15h2 for the recording medium 4 is maintained with high accuracy, thus performing the feeding of the recording medium and the image transfer with high accuracy. During the driving force transmission, the developing sleeve 12d is biased downwardly not only by the rotational reaction force acting on the process cartridge B but also by a reaction force generated when the driving force is transmitted from the flange gear 9c to the sleeve gear 12j. In this case, if the rotary shaft 12d2 of the developing sleeve is not abutted against the abutment portion 33b, the developing sleeve 12d will be always biased downwardly during the image forming operation. As a result, it is feared that the developing sleeve 12d is displaced downwardly and/or the lower frame 15 on which the developing sleeve 12d is mounted is deformed. However, in the illustrated embodiment, since the rotary shaft 12d2 of the developing sleeve is abutted against the abutment portion 33b without fail, the above-mentioned inconvenience does not occur. Incidentally, as shown in Fig. 20 the developing sleeve 12d is biased against the photosensitive drum 9 by the springs 12j via the sleeve bearings 12i. In this case, the arrangement as shown in Fig. 48 may be adopted to facilitate the sliding movement of sleeve bearings 12i. That is to say, a bearing 12m for supporting the rotary shaft 12d2 of the developing sleeve is held in a bearing holder 12n such a manner that the bearing 12m can slide along a slot 12n1 formed in the bearing holder. With this arrangement, as shown in Fig. 49, the bearing holder 12n is abutted against the abutment portion 33b of the shaft support member 33 and is supported thereby; in this condition, the bearing 12m can be slide along the slot 12n1 in directions shown by the arrow. Incidentally, in the illustrated embodiment, an inclined angle  (Fig. 47) of the abutment portion 33b is selected to have a value of about 40 degrees. Further, the developing sleeve 12d may be supported, not via the sleeve rotary shaft. For example, as shown in Figs. 52A and 52B, it may be supported at its both ends portions by sleeve bearings 52 lower ends of which are supported by the lower frame 15 which is in turn supported by receiving portions 53 formed on the image forming system. Further, in the illustrated embodiment, the flange gear 9c of the photosensitive drum 9 is meshed with the drive gear 41 for transmitting the driving force to the flange gear in such a manner that, as shown in Fig. 47, a line connecting a rotational center of the flange gear 9c and a rotational center of the drive gear 41 is offset from a vertical line passing through the rotational center of the flange gear 9c in an anti-clockwise direction by a small angle α (about 1° in the illustrated embodiment), whereby a direction F of the driving force transmission from the drive gear 41 to the flange gear 9c directs upwardly. In general, although the floating of the process cartridge can be prevented by a downwardly directing force generated by setting the angle α to a value of 20° or more, in the illustrated embodiment, such angle α is set to about 1°. By setting the above-mentioned angle α to about 1°, when the upper opening/closing cover 19 is opened in a direction shown by the arrow j to remove the process cartridge B, the flange gear 9c is not blocked by the drive gear 41 and, thus, can be smoothly disengaged from the drive gear 41. Further, when the direction F of the driving force transmission is directed upwardly as mentioned above, the rotary shaft 9f of the photosensitive drum is pushed upwardly and, therefore, tends to be disengaged from the drum supporting portion 33a. However, in the illustrated embodiment, since the overlap portion 33c is formed on the supporting portion 33a, the drum rotary shaft 9f is not disengaged from the drum supporting portion 33a. (Re-cycle) The process cartridge having the above-mentioned construction permits the re-cycle. That is to say, the used-up process cartridge(s) can be collected from the market and the parts thereof can be re-used to form a new process cartridge. Such re-cycle will now be explained. Generally, the used-up process cartridge was disposed or dumped in the past. However, the process cartridge B according to the illustrated embodiment can be collected from the market after the toner in the toner reservoir has been used up, to protect the resources on the earth and the natural environment. Then, the collected process cartridge is disassembled into the upper and lower frames 14, 15 which are in turn cleaned. Thereafter, reusable parts and new parts are mounted on the upper frame 14 or the lower frame 15 at need, and then new toner is supplied into the toner reservoir 12a again. In this way, a new process cartridge is obtained. More particularly, by releasing the connections between the locking pawls 14a and the locking openings 15a, the locking pawls 14a and the locking projection 15b, the locking pawl 14c and the locking opening 15d, and the locking pawl 15c and the locking opening 14b (Figs. 4, 8 and 9) which interconnect the upper and lower frames 14, 15, the upper and lower frames 14, 15 can easily be disassembled from each other. Such disassembling operation can easily be performed, for example, by resting the used-up process cartridge B on a disassembling tool 42 and by pushing the locking pawl 14a by means of a pusher rod 42a, as shown in Fig. 50. Even when the disassembling tool is not used, the process cartridge can be disassembled by pushing the locking pawls 14a, 14c, 15c. After the upper frame 14 and the lower frame 15 are disconnected from each other as mentioned above (Figs. 8 and 9), the frames are cleaned by removing the waste toner adhered to or remaining in the cartridge by an air blow technique. In this case, a relatively large amount of waste toner is adhered to the photosensitive drum 9, developing sleeve 12d and/or cleaning means 13 since they are directly contacted with the toner. On the other hand, the waste toner is not or almost not adhered to the charger roller 10 since it is not directly contacted with the toner. Accordingly, the charger roller 10 can be cleaned more easily than the photosensitive drum 9, developing sleeve 12d and the like. In this regard, according to the illustrated embodiment, since the charger roller 10 is mounted on the upper frame 14 other than the lower frame 15 on which the photosensitive drum 9, developing sleeve 12d and cleaning means 13 are mounted, the upper frame 14 separated from the lower frame 15 can easily be cleaned. In the disassembling and cleaning line as shown in Fig. 39B, first of all, the upper and lower frames 14, 15 are separated from each other as mentioned above. Then, the upper frame 14 and the lower frame 15 are disassembled and cleaned independently. Thereafter, as to the upper frame 14, the charger roller 10 is separated from the upper frame and is cleaned; and as to the lower frame 15, the photosensitive drum 9, developing sleeve 12d, developing blade 12e, cleaning blade 13a and the like are separated from the lower frame and are cleaned. Thus, the disassembling and cleaning line is very simple. After the toner is cleared, as shown in Fig. 9, the opening 12a1 is sealed by a new cover film 28 again, and new toner is supplied into the toner reservoir 12a through the toner filling opening 12a3 formed in the side surface of the toner reservoir 12a, and then the filling opening 12a3 is closed by the lid 12a2. Then, the upper frame 14 and the lower frame 15 are interconnected again by achieving the connections between the locking pawls 14a and the locking openings 15a, the locking pawls 14a and the locking projection 15b, the locking pawl 14c and the locking opening 15d, and the locking pawl 15c and the locking opening 14b, thus assembling a process cartridge again in a usable condition. Incidentally, when the upper and lower frames 14, 15 are interconnected, although the locking pawls 14a and the locking openings 15a, the locking pawls 14a and the locking projection 15b and the like are interlocked, when the same process cartridge is frequently re-cycled, it is feared that the locking forces between the locking pawls and the locking openings become weaker. To cope with this, in the illustrated embodiment, threaded holes are formed in the frames in the vicinity of four corners thereof. That is to say, through threaded holes are formed in the fitting recesses 14d and the fitting projections 14e of the upper frame 14 (Fig. 8) and in the fitting projections 15e (to be fitted into the recesses 14d) and the fitting recesses 15f (to be fitted onto the projections 14e) of the lower frame 15, respectively. Thus, even when the locking force due to the locking pawls become weaker, after the upper and lower frames 14, 15 are interconnected and the fitting projections and fitting recesses are interfitted, by screwing screws in the mated threaded holes, the upper and lower frames 14, 15 can be firmly interconnected. Image forming Operation Next, the image forming operation effected by the image forming apparatus A within which the process cartridge B is mounted will be explained. First of all, the original 2 is rested on the original glass support 1a shown in Fig. 1. Then, when the copy start button A3 is depressed, the light source 1c1 is turned ON and the original glass support 1a is reciprocally shifted on the image forming apparatus in the left and right directions in Fig. 1 to read the information written on the original optically. On the other hand, in registration with the reading of the original, the sheet supply roller 5a and the pair of register rollers 5c1, 5c2 are rotated to feed the recording medium 4 to the image forming station. The photosensitive drum 9 is rotated in the direction d in Fig. 1 in registration of the feeding timing of the paired regist roller 5c1, 5c2, and is uniformly charged by the charger means 10. Then, the light image read by the reading means 1 is illuminated onto the photosensitive drum 9 via the exposure means 11, thereby forming the latent image on the photosensitive drum 9. At the same time when the latent image is formed, the developing means 12 of the process cartridge B is activated to drive the toner feed mechanism 12b, thereby feeding out the toner from the toner reservoir 12a toward the developing sleeve 12d and forming the toner layer on the rotating developing sleeve 12d. Then, by applying to the developing sleeve 12d a voltage having the same charging polarity and same potential as that of the photosensitive drum 9, the latent image on the photosensitive drum 9 is visualized as the toner image. In the illustrated embodiment, the voltage of about 1.2 KW pp, 1590 Hz (rectangular wave) is applied to the developing sleeve 12d. The recording medium 4 is fed between the photosensitive drum 9 and the transfer roller 6. By applying to the transfer roller 6 a voltage having the polarity opposite to that of the toner, the toner image on the photosensitive drum 9 is transferred onto the recording medium 4. In the illustrated embodiment, the transfer roller 6 is made of foam EPDM having the volume resistance of about 10 9 Ωcm and has an outer diameter of about 20 mm, and the voltage of - 3.5 KV is applied to the transfer roller as the transfer voltage. After the toner image was transferred to the recording medium, the photosensitive drum 9 continues to rotate in the direction d. Meanwhile, the residual toner remaining on the photosensitive drum 9 is removed by the cleaning blade 13a, and the removed toner is collected into the waste toner reservoir 13c via the squeegee sheet 13b. On the other hand, the recording medium 4 on which the toner image was transferred is sent, by the convey belt 5d, to the fixing means 7 where the toner image is permanently fixed to the recording medium 4 with heat and pressure. Then, the recording medium is ejected by the pair of ejector rollers 5f1, 5f2. In this way, the information on the original is recorded on the recording medium. Next, other embodiments will be explained. In the above-mentioned first embodiment, while an example that the developing blade 12e and the cleaning blade 13a are attached to the frame by pins 24a, 24b was explained, as shown in Fig. 53, when the developing blade 12e and the cleaning blade 13a are attached to the lower frame 15 by forcibly inserting fitting projections 43a, 43b formed on both longitudinal ends of the developing blade 12e and the cleaning blade 13e into corresponding fitting recesses 44a, 44b formed in the body 16 of the image forming apparatus, pin holes 45 for receiving the pins for attaching the blades 12e, 13a may be formed in the vicinity of the fitting projections 43a, 43b, and corresponding pin holes 45 may be formed in the body 16 of the image forming apparatus (Incidentally, in place of the fitting projections 43a, 43b, half punches or circular bosses may be used). With this arrangement, when the fitting connections between the blades 12e, 13a and the lower frame are loosened by the repeated re-cycle of the process cartridge B, the blades 12e, 13a can be firmly attached to the lower frame by pins. Further, in the first embodiment, as shown in Fig. 29, while an example that the outer diameter D of the photosensitive drum 9 is smaller than the distance L between the drum guide members 25a, 25b to permit the final attachment of the photosensitive drum 9 to the lower frame 15 was explained, as shown in Fig. 54, even when the photosensitive drum 9 is incorporated into the upper frame 14, the outer diameter D of the photosensitive drum 9 may be smaller than the distance L between the drum guide members 25a, 25b so that the photosensitive drum can be lastly incorporated into the upper frame, thereby preventing the surface of the photosensitive drum 9 from damaging, as in the first embodiment. Incidentally, in Fig. 54, elements or parts having the same function as those in the first embodiment are designated by the same reference numerals. Further, the upper and lower frames 14, 15 are interconnected by interlocking locking projections 47a and locking openings 47b and by securing them by pins 48. Further, as shown in Fig. 35, in the first embodiment, while the photosensitive drum 9 and the developing sleeve 12d were supported by the bearing member 26, when the flange gear 9c is provided at one end of the photosensitive drum 9 and the transfer roller gear 49 is provided at the other end of the photosensitive drum, a structure as shown in Fig. 55 may be adopted. Incidentally, also in Fig. 55, elements having the same function as those in the first embodiment are designated by the same reference numerals. More particularly, in Fig. 55, the flange gear 9c and the transfer roller gear 49 are secured to both ends of the photosensitive drum 9 by adhesive, press-fit or the like, respectively, the positioning of the drum is effected by rotatably supporting a central boss 49a of the transfer roller gear 49 by the bearing portion 33a of the bearing member 26. In this case, in order to earth the photosensitive drum 9, a drum earthing plate 50 having a central L-shaped contact portion is secured to and contacted with the inner surface of the drum, and a drum earthing shaft 51 passing through a central bore in the transfer roller gear 49 is always contacted with the drum earthing plate 50. The drum earthing shaft 51 is made of conductive metal such as stainless steel, and the drum earthing plate 50 is also made of conductive metal such as bronze phosphate, stainless steel or the like. When the process cartridge B is mounted within the image forming apparatus A, a head 51a of the drum earthing shaft 51 is supported by the bearing member 26. In this case, the head 51a of the drum earthing shaft 51 is contacted with the drum earthing contact pin of the image forming apparatus, the earthing the photosensitive drum. Also in this case, as in the first embodiment, the positional accuracy between the photosensitive drum 9 and the developing sleeve 12d can be improved by using the single bearing member 26. Further, the process cartridge B according to the present invention can be used to not only form a mono-color image as mentioned above, but also form a multi-color image (two color image, three color image or full-color image) by providing a plurality of developing means 12. Furthermore, the developing method may be of known two-component magnetic brush developing type, cascade developing type, touch-down developing type or cloud developing type. Further, the cleaning means for removing the residual toner remaining on the photosensitive drum 9 may be of fur brush type or magnetic brush type, as well as blade type. Furthermore, the process cartridge B comprises an image bearing member (for example, an electrophotographic photosensitive member) and at least one process means. Therefore, as well as the above-mentioned construction, the process cartridge may incorporate integrally therein the image bearing member and the charger means as a unit which can be removably mounted within the image forming apparatus; or may incorporate integrally therein the image bearing member and the developing means as a unit which can be removably mounted within the image forming apparatus; or may incorporate integrally therein the image bearing member and the cleaning means as a unit which can be removably mounted within the image forming apparatus; or may incorporate integrally therein the image bearing member and two or more process means as a unit which can be removable mounted within the image forming apparatus. That is to say, the process cartridge incorporates integrally therein the charger means, developing means or cleaning means and the electrophotographic photosensitive member as a unit which can be removably mounted within the image forming apparatus; or incorporates integrally therein at least one of the charger means, developing means and cleaning means, and the electrophotographic photosensitive member as a unit which can be removably mounted within the image forming apparatus; or incorporates integrally therein the developing means and the electrophotographic photosensitive member as a unit which can be removably mounted within the image forming apparatus. Further, in the illustrated embodiment, while the image forming apparatus was the electrophotographic copying machine, the present invention is not limited to the copying machine, but may be adapted to other various image forming apparatus such as a laser beam printer, a facsimile, a word processor and the like. Now, the above-mentioned driving force transmission to the photosensitive drum 9 will further explained with more detail. As shown in Fig. 56, the driving force is transmitted from the drive motor 54 attached to the body 16 of the image forming system to a drive gear G6 via a gear train G1 - G5, and from the drive gear G6 to the flange gear 9c meshed with the drive gear, thereby rotating the photosensitive drum 9. Further, the driving force of the drive motor 54 is transmitted from the gear G4 to a gear train G7 - G11, thereby rotating the sheet supply roller 5a. Furthermore, the driving force of the drive motor 54 is transmitted from the gear G1 to the driving roller 7a of the fixing means 7 via gears G12, G13. Further, as shown in Figs. 57 and 58, the flange gear (first gear) 9c and the gear (second gear) 9i are integrally formed and portions of the gears 9c, 9i are exposed from an opening 15g formed in the lower frame 15. When the process cartridge B is mounted within the image forming apparatus A, as shown in Fig. 59, the drive gear G6 is meshed with the flange gear 9c of the photosensitive drum 9 and the gear 9i integral with the gear 9c is meshed with the gear 55 of the transfer roller 6. Incidentally, in Fig. 59, the parts of the image forming apparatus are shown by the solid line, and the parts of the process cartridge are shown by the phantom line. The number of teeth of the gear 9c is different from that of the gear 9i, so that the rotational speed of the developing sleeve 12d when the black image forming cartridge containing the magnetic toner is used is different from the rotational speed of the developing sleeve when the color image forming cartridge containing the non-magnetic toner is used. That is to say, when the black image forming cartridge containing the magnetic toner is mounted within the image forming apparatus, as shown in Fig. 60A, the flange gear 9c is meshed with the sleeve gear 12k of the developing sleeve 12d. On the other hand, when the color image forming cartridge containing the non-magnetic toner is mounted within the image forming apparatus, as shown in Fig. 60B, the gear 9i is meshed with the sleeve gear 12k of the developing sleeve 12d to rotate the developing sleeve. As mentioned above, since the gear 9c has the greater diameter and wider width than those of the gear 9i and has the number of teeth greater than that of the gear 9i, even when the greater load is applied to the gear 9c, the gear 9c can surely receive the driving force to rotate the photosensitive drum 9 surely and transmits the greater driving force to the developing sleeve 12d for the magnetic toner, thereby surely rotating the developing sleeve 12d. By the way, in the above-mentioned first embodiment, as shown in Figs. 6 and 28, as means for preventing the poor transferring by reducing the urging force for urging the recording medium against the image bearing member, while an example that the steps also serving as the guide for guiding the recording medium to the image bearing member is provided on the lower surface of the frame of the process cartridge was explained, other embodiments of such means will now be explained with reference to the accompanying drawings. Fig. 61 is a view of a developing device 12 of a process cartridge B looked at from a side where a photosensitive drum 9 is disposed. In this embodiment, the same elements having the same functions as those in the first embodiment are designated by the same reference numerals. In Fig. 61, the reference numeral 12d denotes a developing sleeve, 12e denotes a developing blade, S denotes toner leakage preventing seals, 12d1 denotes ring abutment portions, and 12k denotes a sleeve gear. As mentioned above, the lower surface of the lower frame 15 also serves as the guide for feeding the recording medium 4, and this lower surface is constituted so that the steps are provided between the central guide portion 15h2 and the both side guide portions 15h1. In this embodiment, the both side guide portions 15h1 each has a thickness T1 of about 5.0 mm and the central guide portion 15h2 has a thickness T2 of about 2.5 mm so as to form the steps. With this arrangement, the feeding space for feeding the recording medium 4 is widened at the central guide portion 15h2, with the result that, even when a thicker recording medium 4 having higher resilience such as a post card, visiting card or envelope is used, it is not feared that the recording medium 4 interferes with the lower surface of the lower frame 15, thus causing the jamming of the recording medium. Further, when a thin recording medium 4 such as a plain sheet having a size larger than the post card is used, since the recording medium 4 is guided by the side guide portions 15h1, it can be fed without floating the recording medium. Further, since the central guide 15h2 is stepped down with respect to the side guide portions 15h1, the flexion of the thicker recording medium 4 having higher resilience such as a post card, visiting card or envelope is reduced, thereby reducing the urging force of the recording medium toward the photosensitive drum 9. In the illustrated embodiment, as mentioned above, since the both side guide portions 15h1 each has the thickness T1 of about 5.0 mm and the central guide portion 15h2 has the thickness T2 of about 2.5 mm, the urging force of the thicker recording medium 4 having higher resilience such as a post card, visiting card or envelope (against the photosensitive drum 9) can be reduced by about 100 grams. Thus, the total urging pressure (against the photosensitive drum 9) combined by the urging force of the recording medium 4 against the photosensitive drum 9 and the urging force (about 400 grams) of the transfer roller against the photosensitive drum becomes about 450 - 600 grams, thus preventing the poor transferring. Furthermore, if the thickness is reduced excessively to form the steps in the lower surface of the lower frame 15, it is feared that the durability of the process cartridge B is reduced or the process cartridge is deformed. However, the process cartridge B according to this embodiment having the above-mentioned values is not deformed even when the durability thereof is expired, and, thus, its strength is satisfactory. Fig. 62 is a view of a developing device 12 of a process cartridge B looked at from a side where a photosensitive drum 9 is disposed, similar to Fig. 61, according to another embodiment. In the process cartridge B shown in Fig. 62, a thickness T3 of the whole guide portion 15h of the lower surface of the lower frame 15 is reduced as thin as possible. However, in order to maintain the strength of the lower surface of the lower frame, reinforcing ribs 56 are formed on the guide portion 15h of lower surface of the lower frame 15 in a criss-cross fashion, and the heights of the ribs 56 are different to form the above-mentioned steps. In the illustrated embodiment, the steps are formed by selecting the total thickness T3 of the guide portion 15h to about 2.0 mm, a height H1 of both side ribs 56a to about 2.0 mm and a height H2 of central ribs 56b to about 0.5 mm. With this arrangement, it is possible to reduce the urging force of the thicker recording medium 4 having higher resilience such as a post card, visiting card or envelope (against the photosensitive drum 9), and, thus, to reduce the total urging pressure (against the photosensitive drum 9) combined by the urging force of the recording medium 4 against the photosensitive drum 9 and the urging force (about 400 grams) of the transfer roller against the photosensitive drum, thus preventing the poor transferring. Incidentally, in the illustrated embodiment, while the steps were formed at a central zone of the lower surface of the lower frame by assuming the fact that the recording medium passes through a central portion of the lower surface of the lower frame, the present invention is not limited to this example. For example, when the recording medium passes through a one side of the lower surface of the lower frame, the steps may be formed on such side area. Fig. 63 is an elevational sectional view of a process cartridge having a protection cover 22 as a protection member for protecting the photosensitive drum 9 from ambient light and dust, and Figs. 64 and 65 are enlarged perspective views of the protection cover 22. Incidentally, the same elements having the same functions as those in the first embodiment are designated by the same reference numerals. In Fig. 63, the reference numerals 5c1, 5c2 denote regist rollers, 6 denotes a transfer roller, 10 denotes a charger roller as the charger means, 12 denotes a developing means, and 13 denotes cleaning means. The protection cover 22 is attached the frame of the process cartridge B via arms 57 (Figs. 64 and 65). As shown in Fig. 63, when the process cartridge B is mounted within the image forming system A, the protection cover can slide toward the developing means 12. Thus, the protection cover 22 serves as a guide portion for guiding the recording medium 4 to the transfer station. In this embodiment, the steps are formed on this protection cover 22. Although the protection cover 22 shown in Fig. 64 also serves as the guide portion for guiding the recording medium 4, since it is the member for protecting the photosensitive drum 9, a thickness T4 of the cover is thick. However, in order to provide the steps, a thickness T5 of both side guide portions 58a for guiding a thin recording medium 4 such as a plain sheet is thinner than the thickness of the cover, and a thickness T6 a central guide portion 58b for guiding a thicker recording medium 4 having the higher resilience such as a post card, visiting card or envelope is thinner than the thickness T5 of the both side guide portions 58a. In this embodiment, it is so selected that the thickness T4 of the protection cover 22 becomes about 7.0 mm, the thickness T5 of the both side guide portions 58a becomes about 4.0 mm and the thickness T6 of the central guide portion 58b becomes about 2.5 mm, thereby defining the steps. With this arrangement, the same technical advantage as that of the previous embodiment can be obtained, thus preventing the poor transferring. On the other hand, in the protection cover 22 shown in Fig. 65, although the total thickness T7 thereof is reduced as thin as possible, reinforcing ribs 59 are formed on the cover in a criss-cross fashion to maintain the strength of the cover. The heights of the reinforcing ribs 59 are differentiated to provide the steps. In this embodiment, it is so selected that the total thickness T7 of the protection cover 22 becomes about 2.0 mm, the height H3 of the both side ribs 59a becomes about 2.0 mm and the height H4 of the central ribs 59b becomes about 0.5 mm, thereby defining the steps. With this arrangement, the same technical advantage as that of the previous embodiment can be obtained, thus preventing the poor transferring. Alternatively, although not shown, the total thickness T7 of the protection cover 22 may be about 2.5 mm, and the central ribs may be omitted and the height H3 of the both side ribs 59a may be about 1.5 mm. Fig. 66 schematically shows a process cartridge B and an image forming apparatus A within which the process cartridge can be mounted. In the system shown in Fig. 66, the compactness (particularly, the reduction in height of the system) can be achieved. That is to say, a photosensitive drum has a reduced diameter of 24 mm, and a developing sleeve has a reduced diameter of 12 mm. A center of the developing sleeve 12 is arranged at a position inclined by an angle γ of 10° in an anti-clockwise direction with respect to a horizontal line passing through the center O of the photosensitive drum 9, thereby reducing the thickness of the process cartridge B itself. (Incidentally, although the greater the angle y the smaller the thickness of the process cartridge B, if the angle γ is greater than 45°, the feeding of the recording medium 4 cannot be effected sufficiently. Thus, the angle γ should be smaller than 45°.) Further, a transfer roller 6 is made of foamed EPDM having the volume resistance of about 10 9 Ωcm and has an outer diameter of about 20 mm, and a transfer voltage of - 3.5 kV is applied to the transfer roller. The transfer roller 6 is rotated in a direction shown by the arrow in Fig. 66, and is biased toward the photosensitive drum 9 by a coil spring 6a and the like. In consideration of the feeding ability for the recording medium 4, the transfer roller may be positioned at a position offset from a vertical line V passing through the center O of the photosensitive drum 9 by an angle α of 1 - 10° toward a recording medium supply means. In this embodiment, the angle α is selected to 1°. In this way, according to this embodiment, although the image forming apparatus A and the process cartridge B are made small-sized by reducing the height of the apparatus A, since the above-mentioned guide portion 15h is provided, it is possible to prevent the poor transferring such as "character void" or "abnormal transferred image", thus providing the good image. Now, the "character void" means a phenomenon that, when the character image is transferred, only the contour of the image is transferred, but the interior of the image is not transferred. This phenomenon is caused by the pressure of the transfer roller. Further, the "abnormal transferred image" means a phenomenon that the crack is generated in the transferred image. This phenomenon is caused by the entrance angle δ (Fig. 67) of the recording medium to a nip between the photosensitive drum and the transfer roller, and does not occur when the recording medium enters into the nip while approaching to the photosensitive drum, and occurs as the entrance angle δ becomes greater. That is to say, in the above-mentioned embodiment, by causing the recording medium 4 to enter the nip along the photosensitive drum 9, not only the "abnormal transferred image" but also "character void" are prevented. More particularly, if the distance between the recording medium feeding path and the process cartridge is reduced in order to reduce the height of the system A as thin as possible and if the lower guide member 23 is approached as long as possible in order to prevent the "abnormal transferred image", particularly, the thicker sheet such as a post card (for example, 128 g/m 2 ) applies a force of 150 - 300 grams to the photosensitive drum by the resilience thereof, and, when the pressure of the transfer roller is added, the "character void" will occur. However, according to the illustrated embodiment, since the guide portion 15h is provided, even if the thicker sheet such as a post card or envelope is used, it is possible to prevent the "character void" by weakening the resilience. In the illustrated embodiment, in consideration of the feeding ability for the recording medium, although the total pressure of the transfer roller 6 is set to about 400 grams, even when the thicker sheet such as a post card or envelope is used, the character void level can be in a range that the character void does not influence upon the transferred image in practice (range 1 - 4 character void level in Fig. 68). Incidentally, in Fig. 68, the character void level 1 is a level having no character void, the level 3 is a level wherein the character void occurs more or less but there is no problem in practice, and the level 5 is a level wherein the severe character void occurs and the toner remains only on the contour of the image. According to the present invention, it is possible to provide a compact and light-weighted process cartridge and an image forming apparatus, which permit the good transferring and can obtain the high quality image, regardless of the kinds of the recording media, for example, even when the recording sheet having high resilience is used.

Claims: An electrophotographic image bearing member (9) in the form of drum which in operation contacts a charging member (10) and to which an oscillatory voltage can be applied so that the image bearing member can be electrically charged, the image bearing member comprising: a photosensitive image bearing layer (9b) capable of bearing an image; a base layer (9a) supporting said image bearing layer; a drive means (9c) disposed at one longitudinal end of said drum and adapted to receive a drive force for rotating the drum; and a cylindrical weight (9d) mounted within the inner surface of said base layer, characterised in that the cylindrical weight is arranged asymmetrically with respect to the longitudinal axis of the drum with its centre displaced towards said drive means. A member according to claim 1, wherein the cylindrical weight contacts the base layer. A member according to claim 1 or claim 2, wherein said driving means is a gear. A member according to claim 3, further comprising a conductive member (18a) contacting said base layer whereby a potential can be applied to the base layer, the conductive member engaging the base layer with a force of 10 to 200g. A member according to claim 4, wherein said conductive member has elasticity. A member according to claim 4 or claim 5, wherein said conductive member contacts the inner surface of said base layer at a plurality of points. A member according to any one of claims 4 to 6, wherein the conductive member contacts the inner surface of said base layer adjacent the longitudinal end of the drum remote from said drive means. A process cartridge mountable on an image forming apparatus, comprising: an image bearing member as claimed in any one of the preceding claims; and a charger member (10) in contact with said image bearing member. A process cartridge according to claim 8, and including developing means for developing an image on said image bearing member using a toner. A process cartridge according to claim 8 or claim 9 and including cleaning means (13a) for cleaning said image bearing member. An image forming apparatus comprising an image bearing member as claimed in any one of claims 1 to 7. An image forming apparatus in combination with a process cartridge as claimed in any one of claims 8 to 10.

Inventors: IKEMOTO ISAO, KOBAYASHI KAZUNORI, NODA SHINYA, SASAGO YOSHIKAZU, SEKINE KAZUMI, SHIMIZU YASUSHI, TSUDA TADAYUKI, WATANABE KAZUSHI, IKEMOTO, ISAO, KOBAYASHI, KAZUNORI, NODA, SHINYA, SASAGO, YOSHIKAZU, SEKINE, KAZUMI, SHIMIZU, YASUSHI, TSUDA, TADAYUKI, WATANABE, KAZUSHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: G03G15
IPC codes: G03G15, G03G21