Electrophotographic image forming apparatus to which a process cartridge is detachably mountable and process cartridge comprising cartridge drum positioning portion or recess

[0002] The present invention relates to an electrophotographic image forming apparatus and a process cartridge removably installable in the main assembly of an electrophotographic image forming apparatus.

[0003] Here, the term “electrophotographic image forming apparatus” refers to an apparatus that forms an image on recording medium with the use of an electrophotographic image forming method. As an example of an electrophotographic image forming apparatus, an electrophotographic copying machine, an electrophotographic printer (for example, a laser beam printer, an LED printer, and the like), a facsimile apparatus, a word processor, and the like can be included.

[0004] A process cartridge is: a cartridge, in which a charging means, either a developing means or a cleaning means, and an electrophotographic photosensitive member, are integrally placed, and which is removably installable in the main assembly of an image forming apparatus; a cartridge in which at least one of the processing means among a charging means, a developing means, and a cleaning means, and an electrophotographic photosensitive drum, are integrally placed, and which is removably installable in the main assembly of an image forming apparatus; or a cartridge in which at least a developing means among the aforementioned processing means, and an electrophotographic photosensitive member, are integrally placed, and which is removably installable in the main assembly of an image forming apparatus.

[0005] Conventionally, an electrophotographic image forming apparatus which employs an electrophotographic image forming process employs a process cartridge system, according to which an electrophotographic photosensitive member, and a single or a plurality of the aforementioned processing means, are integrally placed in a cartridge removably installable in the main assembly of an image forming apparatus. According to this process-cartridge system, an image forming apparatus can be maintained by the users themselves, without relying on service personnel, remarkably improving operational efficiency. Thus, a process-cartridge system is widely used in the field of an image forming apparatus.

[0006] In a process cartridge such as the one described above, a photosensitive drum is driven by the main assembly of an image forming apparatus, and the force for rotationally driving a development sleeve is transmitted to the development sleeve from the photosensitive drum. The force for rotationally driving a stirring member is transmitted also from the photosensitive drum through a gear train.

[0007] In recent years, an image forming apparatus that employs an electrophotographic image forming process has been developed to produce a high quality image without sacrificing its operational efficiency.

[0008] The present invention is a result of further development of the aforementioned conventional technologies.

[0009] The primary object of the present invention is to provide a process cartridge, the electrophotographic photosensitive drum of which is superior in rotational accuracy to a conventional one, and an electrophotographic image forming apparatus in which such a process cartridge is removably installable.

[0010] Another object of the present invention is to provide a process cartridge which can be more accurately positioned relative to the main assembly of an image forming apparatus than a conventional process cartridge, when the process cartridge is installed into the image forming apparatus, and an electrophotographic image forming apparatus in which such a process cartridge is removably installable.

[0011] Another object of the present invention is to provide a process cartridge, the electrophotographic photosensitive drum and cartridge frame of which are positioned, independently from each other, relative to the main assembly of an image forming apparatus when the process cartridge is installed into the image forming apparatus, and an electrophotographic image forming apparatus in which such a process cartridge can be removably installable.

[0012] Another object of the present invention is to provide a process cartridge in which the rotational load is smaller than in a conventional process cartridge, when the electrophotographic photosensitive drum rotates as the force for driving the electrophotographic photosensitive drum is transmitted from the main assembly of an image forming apparatus, and an electrophotographic image forming apparatus in which such a process cartridge can be removably installable.

[0013] These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.

[0014] FIG. 1 is a vertical sectional view of an electrophotographic image forming apparatus.

[0015] FIG. 2 is a vertical sectional view of a process cartridge.

[0016] FIG. 3 is a front view of the process cartridge.

[0017] FIG. 4 is a right side view of the process cartridge.

[0018] FIG. 5 is a left side view of the process cartridge.

[0019] FIG. 6 is a plan view of the process cartridge.

[0020] FIG. 7 is a rear side view of the process cartridge.

[0021] FIG. 8 is a perspective view of the process cartridge as seen from diagonally above the right front.

[0022] FIG. 9 is a perspective view of a process cartridge as seen from diagonally above the right rear.

[0023] FIG. 10 is a perspective view of a process cartridge as seen from diagonally above the right rear, with the process cartridge placed upside down.

[0024] FIG. 11 is a side view of a charging unit.

[0025] FIG. 12 is a side view of the charging unit in FIG. 11, with its blade removed.

[0026] FIG. 13 is a rear view of a developing unit, with its rear cover removed.

[0027] FIG. 14 is a front view of the developing unit, with its front cover removed.

[0028] FIG. 15 is a perspective view of the inward side of the rear cover of the developing unit.

[0029] FIG. 16 is a perspective view of the inward side of the front cover of the developing unit.

[0030] FIG. 17 is a side view of the developing unit.

[0031] FIG. 18 is a front view of the development sleeve supporting portion.

[0032] FIG. 19 is a vertical sectional view of the electrophotographic photosensitive drum supporting portions, and the electrophotographic photosensitive drum driving apparatus, in the first embodiment (before cartridge installation).

[0033] FIG. 20 is a vertical sectional view of the electrophotographic photosensitive drum supporting portions, and the electrophotographic photosensitive drum driving apparatus, in the first embodiment (after cartridge installation).

[0034] FIG. 21 is a perspective view of the drum flange, on the side from which the drum is driven.

[0035] FIG. 22 is a perspective view of the process cartridge as seen from diagonally below the left rear, with the rear cover removed.

[0036] FIG. 23 is a front view of the charging unit.

[0037] FIG. 24 is a sectional view of the charging unit, at the planes indicated by the lines A-B-C-D in FIG. 23.

[0038] FIG. 25 is a perspective view of the charging unit.

[0039] FIG. 26 is a front view of the driving unit on the apparatus main assembly side.

[0040] FIG. 27 is a front view of the driving unit on the apparatus main assembly side, with the front plate in FIG. 26 removed.

[0041] FIG. 28 is a rear view of the driving unit on the apparatus main assembly side.

[0042] FIG. 29 is a sectional view of the driving unit on the apparatus main assembly side, at the planes indicated by the lines F-G-H-I-J-K-L-M in FIG. 28.

[0043] FIG. 30 is a sectional view of the driving unit on the apparatus main assembly side, at the planes indicated by the lines N-O-P-Q-R-S in FIG. 28.

[0044] FIG. 31 is a sectional view of the driving unit on the apparatus main assembly side, at the planes indicated by the lines T-U-V-W-X-Y-Z in FIG. 28.

[0045] FIG. 32 is a rear view of the driving apparatus for the development sleeve, and shows the relationship, in terms of load, among the components in the driving apparatus.

[0046] FIG. 33 is a rear view of the charging roller and its adjacencies, and shows the relationship, in terms of driving force, between the charging roller and the adjacent components involved in the driving of the charging roller.

[0047] FIG. 34 is a perspective view of the portion of the image forming apparatus, in which the cartridge is installed.

[0048] FIG. 35 is a perspective view of the process cartridge in the second embodiment, as seen from diagonally above the right rear.

[0049] FIG. 36 is a sectional view of the electrophotographic photosensitive drum supporting portion, and the electrophotographic photosensitive drum driving apparatus, in the second embodiment of the present invention (before cartridge installation).

[0050] FIG. 37 is a sectional view of the electrophotographic photosensitive drum supporting portion, and the electrophotographic photosensitive of drum driving apparatus, in the second embodiment of the present invention (after cartridge installation).

[0051] Hereinafter, the preferred embodiments of the present invention will be described with reference to the appended drawings.

[0052] In the following description of the embodiments of the present invention, the term “longitudinal direction” means the direction that is perpendicular to the direction in which the recording medium is conveyed, and is parallel to the recording medium. The terms “left” and “right” correspond to the left and right sides of the recording medium when the recording medium is seen from above, and the trailing edge of the recording medium. A term “top side of a process cartridge” means the top side of the process cartridge when the process cartridge is in the main apparatus of an image forming apparatus.

[0053] FIG. 1 is a drawing which depicts one of the electrophotographic image forming apparatuses in accordance with the present invention. This image forming apparatus has: image forming portions that form toner images on a photosensitive drum as an image bearing member; an intermediary transfer belt 4aonto which the toner images are temporarily transferred; a secondary transfer roller 40 as a transferring means for transferring the toner images on the belt 4aonto a recording medium 2; a sheet feeding means for feeding the recording medium 2 into the image forming apparatus main assembly; a conveying means for conveying the recording medium to the transferring means, and more specifically, delivering the recording medium between the intermediary transfer belt 4aand secondary transfer roller 40; a fixing means; and a sheet discharging means.

[0054] Next, the image formation operation in this image forming apparatus will be described.

[0055] As shown in the drawing, there is a sheet feeder cassette in the image forming apparatus. The sheet feeder cassette can hold plural sheets of a recording medium 2 (for example, recording paper, an OHP sheet, fabric, and the like), and is removably installable in the main assembly of an image forming apparatus. After having been fed into the image forming apparatus main assembly by a pickup roller 3bfrom the sheet feeder cassette, each recording medium 2 is separated from the following recording media 2 by a retarding roller pair 3c, and conveyed to a registration roller pair 3gby conveying rollers 3d.

[0056] When the recording medium 2 is conveyed to the registration roller pair 3g, the registration roller pair 3gis not in motion, and the skewing of the recording medium 2 is eliminated as the recording medium 2 is bumped against the nip formed between the two registration rollers 3g.

[0057] In a full-color, image-formation system based on four drums, four process cartridges, that is, a process cartridge BK for yellow color, a process cartridge BM for magenta color, a process cartridge BC for cyan color, and a process cartridge BB for black color, each of which has an image bearing member, are placed in parallel to each other in an image forming apparatus, as shown in the drawing. The image forming apparatus is also provided with optical scanning systems 1Y, 1M, 1C, and 1Bk, which correspond to the process cartridges BK, BM, BC, and BB, one for one in the listed order. A toner image is formed on the photosensitive drum of each of the four process cartridges, by image formation signals. Then, the four toner images, different in color, are transferred in layers onto the intermediary transfer belt 4a, which is running in the direction indicated by an arrow mark, by the transfer rollers 4 (4Y, 4M, 4C, and 4Bk).

[0058] Thereafter, the recording medium 2 is delivered to the secondary transfer roller 40 with a predetermined timing, and the toner images on the intermediary transfer belt 4aare transferred onto the recording medium. Then, the toner images are fixed to the recording medium 2 in the fixing device 5, and the recording medium 2 is discharged into a delivery tray 6 located on top of the apparatus main assembly 14, by discharge roller pairs 3hand 3i, to be accumulated in the delivery tray 6.

[0059] The aforementioned image forming portions, exclusive of the optical scanning systems 1Y, 1M, 1C, and 1Bk, comprise the process cartridges BK, BM, BC, and BB, and toner containers TY, TM, and TC and BK, correspondingly. Since all the process cartridges are the same in structure, the cartridge structure will be described with reference to the process cartridge BK.

[0060] Referring to FIG. 2, the process cartridge BK comprises the photosensitive drum 7, a charging means, an exposing means, and a developing means. The charging means, exposing means, and developing means are placed in the adjacencies of the peripheral surface of the photosensitive drum 7 in a manner to surround the photosensitive drum 7. Further, the process cartridge BK is provided with an opening for image transfer. In this embodiment, it uses two component developer which contains magnetic carrier particles. Thus, the photosensitive drum 7 used in this embodiment may be an ordinary organic photosensitive member or the like. It is preferable that the photosensitive drum 7 is an organic photosensitive member with a surface layer the electrical resistance of which is in a range of 10²-10¹⁴Ω·cm, a photosensitive member based on amorphous silicon, and the like, because such photosensitive members make it possible for electrical charge to be directly injected, and also are effective to prevent ozone generation and to reduce power consumption. In addition, they make it possible to improve charging performance.

[0061] Thus, in this embodiment, a photosensitive, drum is which comprised an aluminum drum as a base member, and a layer of organic photosensitive material placed on the peripheral surface of the aluminum drum, was used as the photosensitive drum 7.

[0062] The charging means is a charging device 8 based on a magnetic brush formed of a magnetic carrier. The charging device 8 comprises a rotatably supported charge roller 8ain the form of a hollow cylinder, and a magnet 8bfixedly placed in the charge roller 8a. After image transfer, the toner remaining on the photosensitive drum 7 is taken into the charging device 8, which rotates in the direction indicated by an arrow mark in the drawing.

[0063] As for the developing means, a developing method in which a layer of two component developer is placed in contact with the peripheral surface of the photosensitive drum 7 (two component, noncontact development) was used.

[0064] FIG. 2 shows the developing means 10 in this embodiment, which develops an electrostatic latent image with the use of a magnetic brush formed of two component developer. The development roller 10dis in the form of a follower cylinder, and is rotatably supported. Within the development roller 10d, a magnet 10cis fixedly placed. The development roller 10drotates in the same direction as the photosensitive drum 7; in the area in which the distance between the peripheral surfaces of the development roller 10dand photosensitive drum 7 is the smallest, the peripheral surfaces of the development roller 10dand photosensitive drum 7 move in the opposite directions. The photosensitive drum 7 and development roller 10dare not placed in contact with each other; a gap within a range of 0.2-1.0 mm is provided between the two, so that only the layer of developer makes contact with the photosensitive drum 7 to develop an electrostatic latent image.

[0065] A mixture toner and carrier is supplied to the development roller 10dby stirring screws 10gand 10hlocated in a casing partitioned with a partition wall 10f. There is provided a gap between each of the longitudinal ends of the partition wall 10f, and the corresponding wall of the casing. As toner is supplied from an unillustrated toner supplying container, it falls into the adjacencies of one of the longitudinal ends of the stirring screw 10g, and then is conveyed to the other longitudinal end of the stirring screw 10g, in other words, the other side of the casing, while being stirred. After reaching the other side of the casing, the toner is moved through the gap between the longitudinal end of the partition wall 10fand the corresponding wall of the casing, into the space in which the stirring screw 10his present, and is returned to the side where it landed from the toner supplying container, while being stirred, by the stirring screw 10h, and is moved through the gap between the partition wall 10fand the corresponding wall of the casing, into the space in which the stirring screw 10gis present. In other words, the toner is circulated, while being stirred, within the casing by the stirring screws 10gand 10h.

[0066] Described next will be the development process in which an electrostatic latent image formed on the photosensitive drum 7 is developed into a visible image, with the use of the developing apparatus 4 which uses a developing method based on a magnetic brush formed of two component developer composed of toner and magnetic carrier, and a developer circulating system. First, as the development roller 10dis rotated, a certain amount of the developer is picked up in a layer onto the peripheral surface of the development roller 10dby the force of the magnet 10c, and is carried in the rotational direction of the development roller 10d. As the layer of developer on the development roller 10dis carried in the rotational direction of the development roller 10d, it is regulated in thickness by a regulating blade 10e, that is, a development blade, positioned perpendicular to the peripheral surface of the development roller 10d. As a result, a thin layer of developer is formed on the development roller 10d. As this thin layer of developer reaches the primary pole of the magnet 10cfor image development, a certain portion of the thin layer of developer is formed into a brush by the magnetic force. The electrostatic latent image on the photosensitive drum 7 is developed by this portion of developer in the form of a brush. Thereafter, this portion of developer on the development roller 10dis returned into the developing means container 10aby the magnetic field the polarity of which is opposite to the primary pole.

[0067] To the development roller 10d, DC voltage and AC voltage are applied from an unillustrated power source. Generally speaking, in a two component developing method, the application of AC voltage increases development efficiency, and also improves image quality. However, it is liable to cause fog. Thus, a certain amount of difference in potential level is provided between the DC voltage applied to the development roller 10dand the surface potential of the photosensitive drum 7, so that toner is prevented from adhering to the non-image areas of the peripheral surface of the photosensitive drum 7.

[0068] This toner image is transferred onto the intermediary transfer belt 4aby an intermediary transferring apparatus 4. The intermediary transferring apparatus 4 comprises an endless belt 4a, which is stretched around a driver roller 4b, a follower roller 4c, and a counter roller 4dfor the secondary transfer roller 40, and is circularly driven in the direction indicated by an arrow mark in FIG. 1. Within the loop of the transfer belt 4a, transfer charge rollers 4Y, 4M, 4C, and 4Bk are disposed, each of which is kept under a predetermined amount of pressure generated from inward side of the loop toward the axial line of the corresponding photosensitive drum, with the endless belt 4apinched between the transfer charge roller and the photosensitive drum. As voltage is applied to each transfer charge roller from a high voltage power source, the endless belt 4ais charged from the inward side of the endless belt loop to the polarity opposite to the toner charge polarity. As a result, the toner image on each photosensitive drum is transferred onto the surface of the intermediary transfer belt 4a, on the outward side of the endless loop.

[0069] As for the material for the intermediary transfer belt 4a, polyimide resin may be employed. However, the selection of the belt material does not need to be limited to polyimide resin. For example, the following materials can be used with satisfactory results: plastics such as polycarbonate resin, polyethylene-terephthalate resin, polyvinyliden fluoride resin, polyethylene naphthalate resin, polyether-ether-keton resin, polyether-sulfone resin, and polyurethane resin; and fluorinated or siliconized rubber.

[0070] After the transfer of the toner image from the photosensitive drum 7, a certain amount of toner (transfer residual toner) remains on the photosensitive drum 7. If this transfer residual toner is allowed to pass, as it is, through the charging device, the areas of the peripheral surface of the photosensitive drum 7 on which the transfer residual toner is present fail to be charged to a satisfactory potential level, and the following image is produced lighter or darker across the areas corresponding to the preceding image (hereinafter, such an anomaly will be referred to as a “ghost”). In other words, in most cases, even when the transfer residual toner comes into contact with the photosensitive drum charging magnetic brush, which is in contact with the peripheral surface of the photosensitive drum 7, the pattern of the preceding image reflected by the transfer residual toner remains virtually intact. Thus, it is necessary to temporarily collect the transfer residual toner into the magnetic brush based charging device 8 as the transfer residual toner reaches the charge station as the photosensitive drum 7 is rotated, so that the trace of the preceding image is erased. In many cases, the transfer residual toner on the photosensitive drum 7 is a mixture of toner particles with a negative polarity, and toner particles the polarity of which have been changed to a positive polarity by the separation discharge, or the like, during image transfer. However, from the standpoint of ease of the collection of the transfer residual toner into the magnetic brush based charging device 8, all transfer residual toner particles are desired to be positive in polarity.

[0071] Thus, in this embodiment, an electrically conductive brush 11 is placed in contact with the peripheral surface of the photosensitive drum 7, between the intermediary transferring apparatus 4 and magnetic brush based charging device 8, to apply a bias opposite in polarity to the charge bias. The positively charged portion of the transfer residual toner passes through the magnetic brush based charging device 8, whereas the negatively charged portion of the transfer residual toner is temporarily captured by the electrically conductive brush 11. The captured portion of the transfer residual toner is deprived of electrical charge by the electrically conductive brush 11, and is sent back onto the photosensitive drum 7. As a result, it becomes easier for the transfer residual toner to be taken in entirety into the magnetic brush.

[0072] (Frame Structure of Process Cartridge)

[0073] The process cartridge B (BK, BM, BC, and BB) comprises a development unit D, and a charge unit C. The development unit D comprises the photosensitive drum 7, the developing means 10, and a developing means frame 12 in which the preceding two components are integrally disposed. The charge unit C comprises the charge roller 8a, the regulating blade 8c, the charge brush 11, and the like, and a charging means frame 13 in which the preceding two components are integrally disposed. In assembling the process cartridge B, first, the development unit D and charge unit C are connected to each other, and a front end cover 16 and a rear end cover 17 (FIG. 4) are attached to the combination of the development unit D and charge unit C from the longitudinal direction of the two units to accurately fix the positional relationship between the development unit D and charge unit C.

[0074] FIGS. 3 to 7 are projection drawings of the process cartridge B (BK, BM, BC, and BB). FIG. 3 is a front view of the process cartridge B; FIG. 4 is a right side view; FIG. 5 is a left side view; FIG. 6 is a plan view; and FIG. 7 is a rear view of the process cartridge. FIGS. 8 to 10 are external perspective views of the process cartridge B. FIG. 8 is a perspective view of the process cartridge B as seen from diagonally above the right front; FIG. 9 is a perspective view as seen from the right rear; and FIG. 10 is a perspective view of the process cartridge B as seen from diagonally above the right rear, with the process cartridge B placed upside down.

[0075] As shown in FIG. 2, the charge unit C comprises the charge roller 8a, the regulating blade 8c, and the electrically conductive brush 11, which are integrally combined with the charging means frame 13. Referring to FIGS. 2, 4, 8, 9, and 10, a portion of the charging means frame 13 constitutes a portion of the shell of the process cartridge B. Referring to FIGS. 2 and 10, the bottom edge 13aof the charging means frame 13 is parallel to the longitudinal direction of the photosensitive drum 7, with the provision of a small gap between the bottom edges 13aand the peripheral surface of the photosensitive drum 7. From this bottom edge 13a, an approximately vertical wall 13bextends upward, constituting another part of the shell of the process cartridge B. The top portion of the approximately vertical wall 13bis bent inward, forming a corner portion 13c. From the corner portion 13c, a top plate 13dwith a roughly key-shaped cross section extends nearly horizontally. There is provided an empty space immediately below the top plate 13d. Below the longitudinal ends of the top plate 13d, component mounting portions 13eand 13fare located, in the front and rear, respectively, which also are integral parts of the top plate 13.

[0076] FIG. 11 is a side view of the charge unit C as seen from the inward side. The front end, or the operator side end, of the charge unit C, with respect to the direction in which the process cartridge B is installed (in the longitudinal direction of the process cartridge B, from the front side of the apparatus main assembly 14) is provided with a charge roller bearing 22 and an end cover 23, which are fixed to the front end of the charge unit C with the same screws. The other end of the charge unit C is provided with a gear unit 24, which is fixed to the rear end of the charge unit C with the use of screws.

[0077] FIG. 12 is a side view of the charge unit C, with the regulating blade 8cand the regulating blade supporting metallic plate 8dremoved. Blade seats 13g, which are the portions raised one for one from the side surfaces of the component mounts 13eand 13f, are provided with a female screw and a dowel-like projection, which are on the flat surfaces to which the regulating blade 8cis attached by their longitudinal ends. The flat surface recessed from the surface of the top surface of the blade seat 13gis provided with a sealing member 21glike a piece of sponge, which is pasted to the flat surface. Further, there is a sealing member 21blike a piece of felt at each of the longitudinal ends of the charge roller 8a. The sealing member 21bis pasted to the charging means frame to prevent developer from leaking outward in the axial direction of the charge roller 8, following the peripheral surfaces of the sealing portions 8a1 located at the longitudinal ends of the charge roller 8a. Therefore, the surfaces of the portions of the charging means frame 13, which meet the sealing portions 8a1 at the longitudinal ends of the charge roller 8a, form an arc, the centers of which coincide with that of the charge roller 8a.

[0078] Referring to FIG. 2, the metallic regulating blade 8cis fixed to the regulating blade supporting metallic plates 8dwith the use of small screws 8j, with the provision of a gap between the regulating blade 8cand charge roller 8a. Both of the regulating blade supporting metallic plates 8dare trough-like in cross section, and have two of holes. When attaching each regulating blade supporting metallic plate 8dto the blade mount 13g, the dowel-like projection 13iof the blade seat 13gof the charging means frame 13 is put through one of the two holes of the regulating blade supporting metallic plate 8d, and a small screw 8kis put through the other hole of the regulating blade supporting metallic plate 8d, and screwed into the female screw 13hof the blade seat 13g. As the small screw 8kis tightened, not only does the regulating blade supporting metallic plate 8dcome into contact with the blade seat 13g, but also the sealing member 21ais compressed by the regulating blade supporting metallic plate 8d. Further, the sealing member 21bis compressed by the regulating blade supporting metallic plate 8d, near the blade seat 13g. The regulating blade supporting metallic plate 8dis extremely high in rigidity, and therefore, attaching it to the charging means frame 21 by its longitudinal ends improves the charging means frame 21 in rigidity.

[0079] (Attaching of Charge Unit)

[0080] Referring to FIG. 11, the charge unit C is supported by the developing means frame 12 in such a manner that the charge unit C is allowed to pivot about a pivotal axis SC illustrated in FIG. 2. Thus, the gear case 26 of the gear unit 24 fixed to the inward end of the charging means frame 13, in terms of the longitudinal direction of the charging means frame 13, is provided with a cylindrical bearing portion 26a, which is positioned so that its axis coincides with the pivotal axis SC, whereas the end cover 23, at the other longitudinal end of the charging means frame 13, is provided with a cylindrical hole 23a, the axis of which coincides with the pivotal axis SC.

[0081] Also referring to FIG. 12, the developing means frame 12 can be roughly divided into four sections: a bottom portion 12f, which contains the aforementioned stirring screws 10gand 10h, in its left and right spaces, respectively, partitioned by the partition wall 10f, and having a blade seat 12eto which the regulating blade 10cis attached; a side portion 12g, which constitutes the left portion of the shell of the process cartridge B as seen from the direction from which the process cartridge B is installed; a side plate 12h(inward side plate) attached to the rear side of the charge unit C in terms of its longitudinal direction; and side plate 12i(front side) attached to the front side of the charge unit C in its longitudinal direction, as shown in FIGS. 13, 14, 17, and 18 as well as in FIG. 2. The end plate 12his provided with a hole 12j, through which a bearing is put to rotationally support the cylindrical shaft portion 26aof the charge unit C. The end plate 12iis provided with a hole 12m, the diameter of which is the same as that of the hole 23aof the charging means frame 13. Thus, when assembling the process cartridge B, first, the round hole 23 of the charge unit C is aligned with the hole 12mof the end plate 12iof the developing means frame 12, with the cylindrical shaft portion 26aof the charge unit C inserted in the hole 12jof the end plate 12hof the developing means frame 12. Then, the rear end cover 17, that is, the end cover on the inward side as seen from the direction in which the process cartridge B is inserted, is aligned with the rear end portion of the developing means frame 13. This allows a hollow, cylindrical, and shaft supporting portion 17a(FIGS. 11 and 15), which projects in the longitudinal direction of the developing means frame 13 from the inward side of the rear end cover 17, to fit into the hole 12jof the developing means frame 12, while allowing the hollow, cylindrical, and shaft-supporting portion 17ato fit around the cylindrical shaft portion 26aof the charge unit C. Further, a supporting shaft 27 (FIGS. 11 and 14), which has been fitted inward of developing means frame 12 through the hole 12mof the end plate 12iof the developing means frame 12, fits into the hole 23aof the charge unit C. As a result, the charge unit C is pivotally supported by the developing means frame 12; more specifically, the cylindrical shaft portion 26aof the charge unit C is rotationally supported by the rear end cover 17, whereas the other end of the charge unit C is supported by the supporting shaft 27 fitted through both the hole 12iof the end plate 12iof the developing means frame 12, and the hole 23aof the charge unit C.

[0082] Referring to FIGS. 6 and 8, to the top portion of the developing means frame 12, a top plate 29 is fixed with the use of small screws 28, with the edges of the top plate 29 placed in contact with the inward side of a guide portion 12a, that is, the top portion of the side wall 12g, and also in contact with the edges of the end plates 12hand 12i.

[0083] Referring to FIG. 2, the top plate 29 is provided with two spring seats 29a, which are located at the longitudinal ends of the top plate 29, one at each end. In each spring seat 29a, a compression coil spring 30 is held, being compressed between the top plate 29 and charging means frame 13. Thus, the charge unit C is kept under the pressure generated by the compression coil springs 30 in a direction to pivot the charge unit C about the pivotal axis SC in the clockwise direction in FIG. 2.

[0084] Referring to FIG. 11, each of the longitudinal end portions of the charge roller 8aforms a journal portion 8a2, which is smaller in diameter than the main portion of the charge roller 8a, and the rotational axis of which is the same as that of the charge roller 8a. Each journal portion 8a2 is fitted with a spacer roller 8nwhich is allowed to freely rotate around the journal portion 8a2. The space rollers 8nare kept in contact with the photosensitive drum 7, outside the image formation range, by the pressure from the aforementioned compression coil springs 8n. With the provision of the above described structure, a gap is provided between the peripheral surfaces of the photosensitive drum 7 and the charge roller 8a. The transfer residual toner is captured by the charge roller 8a, to which a charge bias is being applied, as the transfer residual toner passes through the areas in which the gap between the photosensitive drum 7 and charge roller 8ais smallest, and in this smallest gap, the moving direction of the peripheral surface of the charge roller 8ais opposite to that of the photosensitive drum 7.

[0085] Referring to FIG. 2, the line which connects the pivotal axis SC and the center of the charge roller 8ais virtually perpendicular to the line which connects the centers of the charge roller 8aand photosensitive drum 7.

[0086] Also referring to FIG. 2, the development roller 10dis attached to the developing means frame 12 in a manner to allow the development roller 10dto pivot about the Slv pressure center. Referring to FIG. 17, the journal portions 10d1, that is, the longitudinal end portions of the development roller 10d. which are smaller in diameter than the center portion of the development roller 10d, are fitted with a spacer roller 10j, the outer radius of which is smaller than the radius of the development roller 10dby a gap necessary for image development. On the outward side of each spacer roller 10j, a pivotal arm 32 is located, though the hole of which the journal 10d1 is fitted.

[0087] FIG. 18 is a sectional view of a portion of the process cartridge B, at a plane perpendicular to the development roller 10d, and shows the pivotal arm 32 and its adjacencies. Each pivotal arm 32 is pivotally supported at its base portion by a supporting shaft 33, which has been press-fitted in the end plate 12h(12i) of the developing means frame 12 in the longitudinal direction of the process cartridge B. The pivotal arm 32 is provided with a hole 32awith a bearing surface, which is located virtually straight above the supporting shaft 33. The pivotal arm 32 is also provided with a stopper portion 32b, which is above the hole 32awith a bearing surface. Further, the pivotal arm 32 is provided with a spring seat 37c, the center of which is on a line nearly perpendicular to the line that connects the pressure application center Slv, which is the same as the center of the supporting shaft 33, and the center of the hole 32awith a bearing surface.

[0088] In the hole 32aof the pivotal arm 32, the journal portion 10d1 of the development roller 10dis rotatably supported, at both longitudinal ends of the process cartridge B. Between the spring seat 32cand the spring seat 12nwith which the end plate 12h(12i) of the developing means frame 12 are provided, a compression coil spring 35 is held in the compressed state. With this arrangement, the development roller 10dis enabled to pivot about the pressure application center Slv, and is kept in contact with the photosensitive drum 7 by the pressure from the compression coil springs 35, and also, the spacer rollers 10jare kept in contact with the longitudinal end portions of the photosensitive drum 7, outside the image formation areas, also by the pressure from the compression coil springs 35, providing a predetermined gap (0.2-1.0 mm) between the development roller 10dand the photosensitive drum 7.

[0089] The aforementioned stopper portion 32bis a portion which prevents the pivotal arm 32 from over pivoting in the outward direction in FIG. 18, by coming into contact with the development roller cover 36, during the assembly or disassembly of the process cartridge B. Therefore, in the process cartridge B after its assembly, the stopper 32band developer roller cover 36 are not in contact with each other. The development roller cover 36 extends between the two pivotal arms 32, one at each longitudinal end of the process cartridge B, in the longitudinal direction of the process cartridge B, and is fixed to the developing means frame 12 with the use of screws.

[0090] (Structure for Installing, or Removing, Process Cartridge, into or Out of, Image Forming Apparatus Main Assembly)

[0091] Referring to FIGS. 3 and 7, the top portion of the process cartridge B is provided with guide portions 12aand 29bin the form of a flange, which are located on the left and right side, respectively, as seen from the direction from which the process cartridge B is inserted into the apparatus main assembly. When the process cartridge B is installed into, or removed from, the image forming apparatus main assembly 14, these guide portions 12aand 29bfit into, and are guided by, a pair of guides 14c(FIG. 34) which extend perpendicular to FIG. 1. The guides 14care portions of a guiding member 14bfixed to the apparatus main assembly 14.

[0092] The process cartridge B is provided with various electrical contact points which come into contact with the corresponding electrical contact points connected to an unillustrated high voltage power source, on the apparatus main assembly side, when the process cartridge B is inserted into the apparatus main assembly 14.

[0093] Referring to FIGS. 3 and 8 one of the aforementioned electrical contact points is a drum grounding contact point 101, which is connected to the photosensitive drum 7, and is located on the front side as seen from the direction from which the process 5 cartridge B is installed. Next, referring to FIGS. 7, 9, and 10, located on the rear side, as seen from the direction from which the process cartridge B is installed, are a contact point 102 connected to the electrically conductive brush 11, a charge bias contact point 103 connected to the charge roller 8a, and a development bias contact point 104 connected to the development roller 10d.

[0094] Referring to FIGS. 19 and 20 which are sectional views of the process cartridge B prior to its installation into, and removal from, respectively, the apparatus main assembly 14, as the process cartridge B is inserted into the apparatus main assembly 14, being guided by the guides 14c(FIG. 34) of the apparatus main assembly 14, the leading end of the process cartridge B advances toward the couplings 66, 67, and 68 (FIG. 34) on the driving side, or the main assembly side. Then, the cartridge frame positioning portion 56 on the main assembly side, which is a cartridge positioning boss fixed to the front plate 65 of the drum driving gear unit in such a manner that the axis of the cartridge frame positioning portion 56 coincides with the rotational axis of a shaft 49 for the large gear, that is, a drum driving shaft, and the axis of the bearing 51 for the shaft 49 for the large gear, engages with the cartridge frame positioning portion 17bof the rear end cover 17 of the process cartridge B.

[0095] As FIG. 34 shows, the leading end of the process cartridge B, in terms of the direction in which the process cartridge B is inserted into the apparatus main assembly 14, is provided with three driving force receiving portions, which are shaft couplers, each of which rotates about its own shaft extending in the longitudinal direction of the process cartridge B. These driving force receiving couplers are a cartridge coupling 37d, or the primary coupling of the process cartridge B, with which the drum flange 37 of the photosensitive drum 7 is provided, a charging means driving coupling 38, and a developing means driving coupling 39. They are male couplings. As the process cartridge B is inserted into the apparatus main assembly 14, these three driving force receiving portions are connected to the corresponding driving members on the apparatus main assembly side. These driving members on the apparatus main assembly side are a photosensitive drum driving coupling 66 (52), or the primary coupling, a charging means driving coupling 67, and a developing means driving coupling 68.

[0096] After the process cartridge B is completely inserted into the apparatus main assembly 14, the front cover 116 of the apparatus main assembly 14 is closed onto an unillustrated front plate of the apparatus main assembly 14, from the direction from which the process cartridge B is inserted. As the front cover 116 is closed, the positional relationship between the process cartridge B and the apparatus main assembly 14 is accurately fixed. The front cover 116 is provided with cartridge frame supporting holes 116afor very precisely positioning the four process cartridges BK, BM, BC, and BB relative to the apparatus main assembly 14. The size of each hole 116ais such that the bearing case 54 of the corresponding process cartridge B perfectly fits in the hole 116a.

[0097] Referring to FIG. 7, the rear side of the process cartridge B is provided with the photosensitive drum driving coupling 37d, or the primary cartridge on the cartridge side, the charging means driving coupling 38, and the developing means driving coupling 39, which are exposed from the process cartridge B, but are recessed from the leading end of the process cartridge B.

[0098] (Drum Supporting and Drum Driving Means in First Embodiment)

[0099] The photosensitive drum driving coupling 37dis the leading end portion of the drum flange 37 fixed to the leading end of the photosensitive drum 7, in terms of the direction in which the process cartridge B is inserted into the apparatus main assembly 14.

[0100] FIGS. 19 and 20 show the method for supporting the photosensitive drum 7 and the method for driving the photosensitive drum 7. The photosensitive drum 7, which comprises a hollow aluminum cylinder 7aand a photosensitive layer coated on the peripheral surface of the cylinder 7a, is provided with two drum flanges: a drum flange 37 on the side from which the photosensitive drum 7 is driven, or the driven side, and a drum flange 41 on the side from which the photosensitive drum 7 is not driven, or the non-driven side. The drum flanges 37 and 41 are fixed to the longitudinal ends of the photosensitive drum 7 by being immovably inserted therein, one for one. One end of a drum shaft 42, which has been put through the center hole of the drum flange 37, the aluminum cylinder 7aof the photosensitive drum 7, and the center hole of the drum flange 41, extends through the drum shaft supporting hole 12bof the end plate 12iof the developing means frame 12. The drum shaft 42 is provided with a pin 43, which is press-fitted through the drum shaft 42, in the diameter direction of the drum shaft 42, and across the rotational axis of the drum shaft 42. The pin 43 fits in the groove 41 a with which the flange 41 on the non-driven side is provided. The groove 41ais in the exposed end surface of the flange 41, and extends in the radial direction of the flange 41. In order to connect the drum shaft 42 to the drum cylinder 7ain terms of electricity, an electrically conductive spring 44 is fixed to the inward surface of the drum flange 41 on the non-driven side. As for the method for fixing the electrically conductive spring 44 to the drum flange 41, the electrically conductive spring 44 is fitted around a dowel-like projection 41bprovided on the drum flange 41, and the dowel-like projection 41bis melted and solidified. One end of the electrically conductive spring 44 presses upon, and remains in contact with the inward surface of the drum cylinder 7abecause of its resiliency, and the other end of the spring 44 presses upon, and remains in contact with, the drum shaft 42 also because of its resiliency.

[0101] One end of the drum grounding contact point 101 attached to the end plate 12iof the developing means frame 12 presses upon, and remains in contact with, the drum shaft 42 because of its resiliency, whereas the other end of the drum grounding contact point 101 is exposed from the process cartridge B, constituting an external contact point.

[0102] For ease of assembly, the surface of the drum supporting hole 12bof the end plate 128 is provided with a pair of grooves 12c, which are deep enough in the radial direction of the hole 12c, so that the pin 43 can be put through the end plate 12iin the longitudinal direction of the drum shaft 42 (FIG. 14).

[0103] The driven side drum flange 37 has an anchor portion 37awhich engages with the cylinder 7a, a flange portion 37b, the inwardly facing surface of which contacts the edge of the cylinder 7a, a cylindrical projection 37c, the diameter of which is smaller than that of the flange portion 37b, and photosensitive drum driving coupling 37d, that is, a portion projecting in the axial direction of the photosensitive drum 7 from the center portion of the outwardly facing surface of the cylindrical projection 37c, listed from the front side of the apparatus. The driven side drum flange 37 is a single-piece component formed of plastic.

[0104] The cylindrical projection 37cis temporarily fitted into a rear side cylindrical portion 17a, which is an integral part of the rear end cover 17 fitted in the hole 12dof the end plate 12h, projects inward of the process cartridge B, and serves as a shaft supporting portion. With the cylindrical projection 37ctemporarily fitted in the cylindrical portion 17a, there is a gap of 0.2-1.0 mm between the peripheral surface of the circular projection 37cand the inward surface of the rear side cylindrical portion 17a, allowing the circular projection 37c(photosensitive drum 7) to freely rotate.

[0105] Referring to FIG. 21, the photosensitive drum driving coupling 37dis a twisted equilateral triangular projection, the central axis of which coincides with that of the drum shaft 42. The diameter of the circumcircle of this triangular projection is smaller than that of the cylindrical projection 37c.

[0106] Referring to FIG. 36, the driving apparatus provided on the apparatus main assembly side has a fixedly disposed motor 45, a pinion 46 fixed to the shaft of the motor 45, an intermediary gear 47 which is rotatably supported and is meshed with the pinion 46 and a large diameter gear 48, a driving shaft 49, to which the large diameter gear 48 is fixed, and to the inward end of which a main assembly side coupling 52, and a bearing 51, which bears the driving shaft 49. Incidentally, the intermediary gear 47 may be a step gear, for example, a gear with a single step. The portion of the driving shaft 49, where the main assembly side coupling 52 fits, may be given a D-shaped cross section, for example, so that the rotation of the driving shaft 49 is reliably transmitted. The main assembly side coupling 52 is allowed to freely move in the driving shaft direction. Between the bearing 51 on the inward side of the process cartridge, and the main assembly side coupling 52, a compression coil spring 50 is positioned around the driving shaft 49 in the compressed state. The main assembly side coupling 52 transmits the force generated by the compression coil spring 50 to the driving shaft 49 through a flange 49aintegral with the driving shaft 49. With the provision of the above arrangement, the positions of the driving shaft 49 and main assembly side coupling 52 in terms of the shaft direction are fixed.

[0107] The bearing 51 rotatably supports the driving shaft 49. The actual coupling portion 52aof the main assembly side coupling 52 is a hole in the form of a twisted equilateral triangular pillar, and the cartridge side coupling 37dis engaged into, or disengaged from, the hole 52aof the main assembly side coupling 52, in the shaft direction. As the cartridge side coupling 37dand hole 52aengage with each other, the ridges of the twisted equilateral triangular projection, that is, the projection of the cartridge side coupling 37dcome into contact with the walls of the twisted equilateral triangular hole of the hole 52aof the main assembly coupling 52. As a result, the rotational axes of the projection and hole become aligned with each other. A drum positioning portion 57 on the apparatus main assembly side, which is the shaft centering inward end portion of the driving shaft 49, and the main assembly side coupling 52, are provided with a microscopic amount of tolerance.

[0108] As the above described two coupling portions engage each other, the main assembly side coupling 52 is positioned as close as possible to the process cartridge B, while being allowed to be pushed back outward of the process cartridge B against the force from the compression coil spring 50 (detailed description will be omitted).

[0109] Referring to FIGS. 19 and 20, the drum shaft supporting portion on the non-driven side is structured to prevent the drum shaft 42 from shifting toward the non-driven side. The front side end of the drum shaft 42 is fitted in a bearing 55 encased in a bearing case 54 fixed to the front end cover 16 fixed to the end plate 128 of the developing means frame 12. The movement of the drum shaft 42 toward the nondriven side is prevented by the contact between the front end of the drum shaft 42 and the bottom surface of the pouch-like blind hole of the bearing case 54. On the driven side, the end portion of the drum shaft 42 is fitted in the hole 37eof the drum flange 37. The drum flange 37 is prevented from being excessively moved toward driven side, by the contact between the outwardly facing surface of the flange portion 37bof the drum flange 3, and the edge of the cylindrical portion 17aof the rear cover 17, which projects inward of the process cartridge B. In the above described structure, in order to allow the photosensitive drum 7 a limited amount of movement in its axial direction, the distance between the edge of the cylindrical portion 17aof the rear cover 17 and the bearing case 54, is rendered greater than the distance between the outwardly facing surface of the drum flange portion 37band the outwardly facing surface of the non-driven side flange 41.

[0110] Since the driving apparatus is structured as described above, as the process cartridge B is inserted into the image forming apparatus main assembly 14, the position of the cartridge frame (developing means frame 12, front end cover 16, and rear end cover 17) relative to the apparatus main assembly 14 is fixed. More specifically, the drum position fixing portion 57 on the main assembly side, that is, the shaft centering portion, which is the inward end of the driving shaft 49, is fitted into the drum position fixing portion 37fon the cartridge side, which is the center hole of the drum flange 37, and at the same time, the coupling 37don the cartridge side, that is, a projection, engages into the coupling hole 52aof the coupling 52 on the main assembly side. As a result, the driven side end of the photosensitive drum 7 is supported, with its rotational axis in alignment with the rotational axis of the driving shaft 49, by the drum position fixing portion 57, that is, the driving shaft centering portion on the apparatus main assembly side, with the provision of a gap between the photosensitive drum 7 and cartridge frame. On the other hand, on the nondriven side, the bearing case 54, which holds the bearing 55 having been press-fitted into the bearing case 54, is inserted into the cartridge frame supporting hole 116aof the front cover 116 of the apparatus main assembly 14, being thereby supported by the front cover 116. Therefore, the position of the photosensitive drum 7 is virtually directly fixed relative to the main assembly frame. Incidentally, the front cover 116 is accurately positioned relative to the main assembly frame when it is attached to the main assembly frame.

[0111] In this embodiment, after the coupling of the drum positioning portion 57 on the main assembly side, that is, the inward end portion of the driving shaft 49, into the drum positioning portion 37fon the cartridge side, the gap between the peripheral surface of the drum positioning portion 57 and the inward surface of the drum positioning portion 37fis in a range of 10 μm-30 μm. Further, the gap between the inward surface of the inwardly projecting cylindrical portion 17a, and the peripheral surface of the cylindrical projection 37cof the flange 37 is in a range of 0.2 mm-0.4 mm.

[0112] As the motor 45 rotates, the pinion gear 46, the intermediary gear 47, the large diameter gear 48, the driving shaft 49, and the main assembly side coupling 52, rotate. As the main assembly side coupling 52 rotates, the cartridge side coupling 37dand coupling hole 52a, which are in the form of a twisted equilateral triangular pillar, are caused to pull each other in such a manner that a male screw is screwed into a female screw. As a result, the drum flange 37 and main assembly side coupling 52 pull each other. Eventually, the end of the cartridge side coupling 37dcomes into contact with the bottom surface of the coupling hole 52a, fixing the position of the photosensitive drum 7 relative to the main assembly side coupling 52, the position of which is virtually fixed; in other words, the position of the photosensitive drum 7 relative to the apparatus main assembly 14 in terms of the longitudinal direction is fixed. In this state, there is no contact between the inward surface of the aforementioned rearwardly projecting cylindrical portion 17aand the peripheral surface of the cylindrical projection 37cof the flange 37; the gap between the two surfaces is in a range of 0.2 mm-0.4 mm. There is no friction between the two surfaces, reducing the overall frictional resistance load which applies to the photosensitive drum 7.

[0113] In a situation in which the cartridge side coupling 37dfails to engage the coupling hole 52aon the main assembly side after the installation of the apparatus main assembly 14, the main assembly side coupling 52 will have been pushed back against the force from the compression coil spring 50, by the rearwardly facing surface of the cartridge side coupling 37d, which will have come into contact with the edge of the opening of the coupling hole 52a. Therefore, as soon as the rotational phase of the cartridge side coupling 37dis caused to match that of coupling hole 52a, by the aforementioned rotation of the main assembly side coupling 52 after the installation of the process cartridge B, the two couplings instantly engage each other.

[0114] (Photosensitive Drum Supporting and Driving Means, in Second Embodiment)

[0115] This embodiment is a modification of the first embodiment. More specifically, the rear end cover 17, which is one of the components of the cartridge frame 130, of the photosensitive drum supporting and driving means in this embodiment, is a modified version of the rear end cover 17 in the first embodiment. Otherwise, the photosensitive supporting and driving means in this embodiment is the same in structure as that in the first embodiment. Thus, this embodiment will be described regarding only its difference from the first embodiment, while referring to the first embodiment.

[0116] Referring to FIG. 22, the surface of the rear end cover 17 of the process cartridge B in the first embodiment, which faces the direction toward which the process cartridge B is inserted, is practically flat. Referring to FIG. 35, in this embodiment, however, the end surface 17chas a projection 17ewhich projects in the downstream direction in terms of the direction in which the process cartridge B is inserted. This projection 17eis cylindrical. Next, referring to FIG. 36, the cylindrical inward wall portion of this cylindrical projection 17econstitutes a part of the cartridge frame positioning portion 17b. The edge of the opening of the projection 17ehas been chambered on the inward side, providing a surface 17f. In other words, the cylindrical, cartridge frame positioning portion 17bis the portion of the rear end cover 17 that extends inward of the rear end cover 17 from the inward edge of the slanted surface 17f(chamfer) of the cylindrical projection 17e. From the inward side of this cylindrical, cartridge frame positioning portion 17b, as seen from the entrance side of the cartridge frame positioning portion 17b, an intermediary cylindrical portion 17gextends inward. Also as seen from the entrance side of the cartridge frame positioning portion 17b, the intermediary cylindrical portion 17gextends inward from the inward side of the cartridge frame positioning portion 17b, and the innermost cylindrical portion 17aextends inward from the inward side of the intermediary cylindrical portion 17g. These intermediary and innermost cylindrical portions 17gand 17agradually are reduced in internal diameter toward the upstream side in terms of the direction in which the process cartridge B is inserted; in other words, their internal diameters gradually are reduced toward the inward side of the process cartridge B. Further, the inward end of the innermost cylindrical portion 17ais provided with a flange 17a-1 which extends inward of the innermost cylindrical portion 17a, in terms of the radial direction of the innermost cylindrical portion 17a, in other words, toward the peripheral surface of the cylindrical projection 37cof the drum side flange 37. The internal diameter of the flange 17a-1 is such that a gap in a range of 0.2 mm-0.4 mm is provided between the inward edge of the flange 17a1, and the peripheral surface of the cylindrical projection 37c.

[0117] The function of this photosensitive drum supporting and driving means in this second embodiment is practically the same as that of the photosensitive drum supporting and driving means in the first embodiment, except for the following effect. That is, since the internal diameters of the cylindrical portions 17gand 17a, which are on the inward side of the cartridge frame positioning portion 17b, are gradually reduced toward the inward side of the process cartridge B, it is easier for the rear end cover 17 to be released from the mold. Further, since the rear end portion of the cylindrical, cartridge frame positioning portion projects rearward from the end cover 17 (cartridge frame), it is better assured that the cartridge frame positioning portion on the process cartridge side engages with the cartridge frame positioning portion on the main assembly side.

[0118] Incidentally, although the preceding embodiments of the present invention were described with reference to the process cartridge B which integrally comprised developing means, the charging means, and the photosensitive drum, the structure for supporting the photosensitive drum by the cartridge frame, and the structure for allowing the driving force receiving portion of the photosensitive drum and the cartridge driving member of the image forming apparatus main assembly, to be engaged with, or be disengaged from, each other, in the preceding embodiments. are applicable to process cartridges in general.

[0119] The embodiments are summarized as follows:

[0120] 1. A process cartridge B detachably mountable to a main assembly 14 of an electrophotographic image forming apparatus, comprising:

[0121] a cartridge frame 130;

[0122] an electrophotographic photosensitive drum 7 supported on the cartridge frame 130;

[0123] wherein the photosensitive drum 7 has a downstream side end, with respect to a mounting direction in which the process cartridge B is mounted to the main assembly 14 of the apparatus in the axial direction of the photosensitive drum 7, and is supported on the cartridge frame 130 for movement in a direction crossing with the axis direction of the photosensitive drum 7;

[0124] process means actable on the photosensitive drum 7;

[0125] a cartridge drum 7 positioning portion 37ffor positioning the photosensitive drum 7 to the main assembly 14 of the apparatus by engagement with a main assembly 14 drum 7 positioning portion 57 provided in the main assembly 14 of the apparatus when the process cartridge B is mounted to the main assembly 14 of the apparatus, wherein the cartridge drum 7 positioning portion 37fis disposed coaxially with the photosensitive drum 7;

[0126] a cartridge frame 130 positioning portion for positioning the cartridge frame 130 to the main assembly 14 of the apparatus by engagement with a main assembly 14 frame positioning portion 56 provided in the main assembly 14 of the apparatus when the process cartridge B is mounted to the main assembly 14 of the apparatus;

[0127] wherein the cartridge frame 130 positioning portion is disposed at a leading end portion with to respect to a mounting direction in which the process cartridge B is mounted to the main assembly 14 of the apparatus, and the cartridge frame 130 positioning portion is disposed so as to be coaxial with the photosensitive drum 7 when the cartridge drum 7 positioning portion 37fis engaged with the main assembly 14 drum 7 positioning portion 57 so that the photosensitive drum 7 is positioned to the main assembly 14 of the apparatus.

[0128] 2. A process cartridge B according to Item 1, wherein the cartridge frame 130 positioning portion is a positioning cylindrical portion 17bextended in the cartridge frame 130 in the mounting direction.

[0129] 3. A process cartridge B according to Item 2, wherein the positioning cylindrical portion 17bis projected outwardly from a leading end surface of the cartridge frame 130, and the positioning cylindrical portion 17bis extended from outside of the cartridge frame 130 to an inside thereof.

[0130] 4. A process cartridge B according to Item 1, 2 or 3, wherein a rear side cylindrical portion is provided at a rear side of the positioning cylindrical portion 17b, and a circular projected portion of a flange 37 of the photosensitive drum 7 enters an upstream side end of the rear side cylindrical portion in the mounting direction, and a gap G of 0.2 mm-0.4 mm is provided between an inner surface of said rear side cylindrical portion and an outer surface of the circular projected portion, and the rear side cylindrical portion is disposed substantially coaxially with the positioning cylindrical portion 17b.

[0131] 5. A process cartridge B according to Item 1, 2 or 3, wherein the inner diameter of the positioning cylindrical portion 17bis 25 mm-27 mm, and the length thereof is 8 mm-10 mm.

[0132] 6. A process cartridge B according to Item 1, 2 or 3, wherein the positioning cylindrical portion 17band rear side cylindrical portion are made of resin material, and are integrally molded with an end cover 16 or 17 of resin material as a part of a cartridge frame 130.

[0133] 7. A process cartridge B according to Item 4, further comprising a cartridge coupling, at a leading end of the circular projected portion, for receiving a driving force for rotating the photosensitive drum 7 through a main assembly 14 coupling 52 provided in the main assembly 14 of the apparatus when the process cartridge B is mounted to the main assembly 14 of the apparatus.

[0134] 8. A process cartridge B according to Item 7, wherein the cartridge drum 7 positioning portion 37fis in the form of a recess formed substantially at a center of the cartridge coupling.

[0135] 9. A process cartridge B according to Item 1, wherein a cartridge drum 7 positioning portion 37fis a recess formed at a center of a flange 37 of the photosensitive drum 7, wherein the flange 37 is mounted to a downstream side end of cylinder of the photosensitive drum 7.

[0136] 10. A process cartridge B according to Item 9, wherein the flange 37 has a circular projected portion, and a free end of the circular projected portion is provided with a cartridge coupling for receiving a driving force for rotating the photosensitive drum 7 through a main assembly 14 coupling 52 provided in the main assembly 14 of the apparatus, wherein the recess is disposed substantially at center portions of a cartridge 25 coupling and the circular projected portion.

[0137] 11. A process cartridge B according to Item 8 or 10, wherein the cartridge coupling has a substantially triangular prism which is twisted, and the main assembly 14 coupling 52 has a twisted hole having a substantially triangular cross-section, corner portions of the substantially triangular prism are beveled, and a recess as the cartridge drum 7 positioning portion 37fis provided substantially at the center of the substantially triangular prism.

[0138] 12. A process cartridge B according to Item 8, 9, wherein when the process cartridge B is mounted to the main assembly 14 of the apparatus, a driving shaft 46 as the main assembly 14 drum 7 positioning portion 57 provided in the main assembly 14 of the apparatus is engaged with the recess, and the main assembly 14 coupling 52 provided at a free end portion or leading end portion of the shaft is engaged with cartridge coupling, by which the position of the photosensitive drum 7 in a direction crossing with a direction of an axis, and a rotating force for rotating the photosensitive drum 7 is transmitted from main assembly 14 of the apparatus, the driving shaft 46 is rotatable by a driving force from a motor provided in the main assembly 14 of the apparatus.

[0139] 13. A process cartridge B according to Item 12, wherein the amount of press-fitting is 10 μm and a gap G between the driving shaft 46 and the recess is 30 μm in a direction crossing with an axis of the driving shaft 46.

[0140] 14. A process cartridge B according to Item 1 or 13, wherein an upstream side end of the photosensitive drum 7 with respect to a mounting direction, is rotatably supported on the cartridge frame 130 so as not to be movable in a direction crossing with a direction of the axis of the photosensitive drum 7.

[0141] 15. A process cartridge B according to Item 1, wherein the process means includes at least one of developing means for developing an electrostatic latent image formed on the photosensitive drum 7, charging means for charging the photosensitive drum 7, and cleaning means for removing a developer remaining on the photosensitive drum 7.

[0142] 16. A process cartridge B detachably mountable to a main assembly 14 of an electrophotographic image forming apparatus, comprising:

[0143] a cartridge frame 130;

[0144] an electrophotographic photosensitive drum 7 supported on the cartridge frame 130;

[0145] wherein the photosensitive drum 7 has a downstream side end, with respect to a mounting direction in which the process cartridge B is mounted to the main assembly 14 of the apparatus in the axial direction of the photosensitive drum 7, is supported on the cartridge frame 130 for movement in a direction crossing with the axis direction of the photosensitive drum 7;

[0146] a developing roller for developing an electrostatic latent image formed on the photosensitive drum 7;

[0147] a charging roller for charging the photosensitive drum 7;

[0148] a cartridge drum 7 positioning recess for positioning the photosensitive drum 7 to a main assembly 14 of the apparatus by engagement with a main assembly 14 drum 7 positioning portion 57 provided in the main assembly 14 of the apparatus when the process cartridge B is mounted to the main assembly 14 of the apparatus;

[0149] wherein a cartridge drum 7 positioning recess is disposed coaxially with the photosensitive drum 7, and the cartridge drum 7 positioning recess is provided at a center of a circular projected portion of a flange 37 of the photosensitive drum 7, and wherein the flange 37 is mounted at one end portion of a cylinder of the photosensitive drum 7 in an axis direction;

[0150] a positioning cylindrical portion 17bfor positioning the cartridge frame 130 to a main assembly 14 of the apparatus by engagement with a main assembly 14 frame positioning portion 56 provided in the main assembly 14 of the apparatus when the process cartridge B is mounted to the main assembly 14 of the apparatus;

[0151] wherein the positioning cylindrical portion 17bis disposed at a leading end, with respect to a mounting direction in which the process cartridge B is mounted to the main assembly 14 of the apparatus, and the positioning cylindrical portion 17bis disposed such that it is coaxial with the photosensitive drum 7 when a cartridge drum 7 is positioning to the main assembly 14 of the apparatus by engagement of the cartridge drum 7 positioning recess with the main assembly 14 drum 7 positioning portion 57, and the positioning cylindrical portion 17bis extended in the mounting direction on the cartridge frame 130, and the positioning cylindrical portion 17bis outwardly projected from a free end surface of the cartridge frame 130, and the positioning cylindrical portion 17bis extended from outside to inside of the cartridge frame 130;

[0152] a cartridge coupling for receiving a driving force for rotating the photosensitive drum 7 through a main assembly 14 coupling 52 provided in the main assembly 14 of the apparatus when the process cartridge B is mounted to the main assembly 14 of the apparatus, and the recess is disposed at the center of the cartridge coupling and the circular projected portion.

[0153] 17. A process cartridge B according to Item 16, wherein a rear side cylindrical portion is provided at a rear side of the positioning cylindrical portion 17b, and the circular projected portion enters an upstream side end of the rear side cylindrical portion, wherein a gap G of 0.2-0.4 mm is formed between an inner surface of the rear side cylindrical portion and an outer surface of the circular projected portion, wherein the rear side cylindrical portion is substantially coaxial with the positioning cylindrical portion 17b.

[0154] 18. A process cartridge B according to Item 17, wherein the inner diameter of the positioning cylindrical portion 17bis 25 mm-27 mm, and the length thereof is 8 mm-10 mm.

[0155] 19. A process cartridge B according to Item 16, 17, 18, wherein the positioning cylindrical portion 17band rear side cylindrical portion are made of resin material, and are integrally molded with an end cover 16 or 17 of resin material as a part of a cartridge frame 130.

[0156] 20. A process cartridge B according to Item 16, 17, 18 or 19, wherein when the process cartridge B is mounted to the main assembly 14 of the apparatus, a driving shaft 46 as the main assembly 14 drum 7 positioning portion 57 provided in the main assembly 14 of the apparatus is engaged with the recess, and the main assembly 14 coupling 52 provided at a free end portion or leading end portion of the shaft is engaged with cartridge coupling, by which the position of the photosensitive drum 7 in a direction crossing with a direction of an axis, and a rotating force for rotating the photosensitive drum 7 is transmitted from main assembly 14 of the apparatus, the driving shaft 46 is rotatable by a driving force from a motor provided in the main assembly 14 of the apparatus.

[0157] 21. A process cartridge B according to Item 20, wherein the amount of press-fitting is 10 μm—and the gap G between the driving shaft 46 and the recess is 30 μm in a direction crossing with an axis of the driving shaft 46.

[0158] 22. A process cartridge B according to Item 16 or 21, wherein an upstream side end of the photosensitive drum 7 with respect to a mounting direction, is rotatably supported on the cartridge frame 130 so as not to be movable in a direction crossing with a direction of the axis of the photosensitive drum 7.

[0159] 23. An electrophotographic image forming apparatus for forming an image on a recording material, to which a process cartridge B is detachably mountable, comprising:

[0160] (a) a main assembly 14 drum 7 positioning portion 57;

[0161] (b) a main assembly 14 frame positioning portion 56;

[0162] (c) a mounting member for detachably mounting a process cartridge B, the process cartridge B including:

[0163] a cartridge frame 130;

[0164] an electrophotographic photosensitive drum 7 supported on the cartridge frame 130;

[0165] wherein the photosensitive drum 7 has a downstream side end, with respect to a mounting direction in which the process cartridge B is mounted to the main assembly 14 of the apparatus in the axial direction of the photosensitive drum 7, and is supported on the cartridge frame 130 for movement in a direction crossing with the axis direction of the photosensitive drum 7;

[0166] process means actable on the photosensitive drum 7;

[0167] a cartridge drum 7 positioning portion 37ffor positioning the photosensitive drum 7 to the main assembly 14 of the apparatus by engagement with the main assembly 14 drum 7 positioning portion 57 when the process cartridge B is mounted to the main assembly 14 of the apparatus, wherein the cartridge drum 7 positioning portion 37fis disposed coaxial with the photosensitive drum 7; and

[0168] a cartridge frame 130 positioning portion for positioning the cartridge frame 130 to a main assembly 14 of the apparatus by engagement with a positioning portion of the main assembly 14 frame when the process cartridge B is mounted to the main assembly 14 of the apparatus, wherein the cartridge frame 130 positioning portion is disposed at a leading end with respect to a mounting direction of the process cartridge B relative to the apparatus, and the cartridge frame 130 positioning portion is disposed in the cartridge frame 130 such that when the photosensitive drum 7 is positioned to the main assembly 14 of the apparatus by engagement of the cartridge drum 7 positioning portion 37fwith the main assembly 14 drum 7 positioning portion 57, it is coaxial with the photosensitive drum 7.

[0169] 24. An electrophotographic image forming apparatus for forming an image on a recording material, to which a process cartridge B is detachably mountable, comprising:

[0170] (a) a main assembly 14 drum 7 positioning portion 57;

[0171] (b) a main assembly 14 frame positioning portion 56;

[0172] (c) a main assembly 14 coupling 52;

[0173] (d) a mounting member for detachably mounting a process cartridge B, the process cartridge B including:

[0174] a cartridge frame 130;

[0175] an electrophotographic photosensitive drum 7 supported on the cartridge frame 130;

[0176] wherein the photosensitive drum 7 has a downstream side end, with respect to a mounting direction in which the process cartridge B is mounted to the main assembly 14 of the apparatus in the axial direction of the photosensitive drum 7, is supported on the cartridge frame 130 for movement in a direction crossing with the axis direction of the photosensitive drum 7;

[0177] a developing roller for developing an electrostatic latent image formed on the photosensitive drum 7;

[0178] a charging roller for charging the photosensitive drum 7;

[0179] a cartridge drum 7 positioning recess for positioning the photosensitive drum 7 to the main assembly 14 of the apparatus by engagement with the main assembly 14 drum 7 positioning portion 57 when the process cartridge B is mounted to the main assembly 14 of the apparatus, wherein the cartridge drum 7 positioning recess is disposed coaxially with the photosensitive drum 7, and the cartridge drum 7 positioning recess is provided at the center of a circular projected portion of a flange 37 of the photosensitive drum 7, and the flange 37 is mounted to one axial end of a cylinder of the photosensitive drum 7;

[0180] a positioning cylindrical portion 17bfor positioning the cartridge frame 130 to the main assembly 14 of the apparatus by engagement with the main assembly 14 frame positioning portion 56 when the process cartridge B is mounted to the main assembly 14 of the apparatus;

[0181] wherein the positioning cylindrical portion 17bis disposed at a leading end, with respect to a mounting direction in which the process cartridge B is mounted to the main assembly 14 of the apparatus,

[0182] wherein the positioning cylindrical portion 17bis disposed on the cartridge frame 130 such that when the photosensitive drum 7 is positioned in the main assembly 14 of the apparatus by engagement of the cartridge drum 7 positioning recess with the main assembly 14 drum 7 positioning portion 57, it is coaxial with the photosensitive drum 7,

[0183] wherein the positioning cylindrical portion 17bis extended along the mounting direction on the cartridge frame 130, and the positioning cylindrical portion 17bis projected outwardly from a leading end surface of the cartridge frame 130, and the positioning cylindrical portion 17bis extended from outside of the cartridge frame 130 to inside thereof;

[0184] a cartridge coupling, provided at a leading edge of the circular projected portion, for receiving a driving force for rotating the photosensitive drum 7 through a main assembly 14 coupling 52 when the process cartridge B is mounted to the main assembly 14 of the apparatus, wherein the recess is disposed substantially at center portions of the circular projected portion and the cartridge coupling.

[0185] According to the embodiments described above, when the process cartridge B is installed into the image forming apparatus main assembly 14, the positional relationship between the photosensitive drum 7 and the apparatus main assembly 14, and the positional relationship between the cartridge frame 100 and the apparatus main assembly 14, are independently fixed. Therefore, the vibrations of the cartridge frame 100 are not transmitted to the photosensitive drum 7. As a result, the degree of accuracy with which the photosensitive drum 7 is rotated is improved. Further, since the position of photosensitive drum 7 relative to the apparatus main assembly 14 is fixed independently from that of the cartridge frame 100, the positioning accuracy for the photosensitive drum 7 is also improved.

[0186] (Driving of Development Roller)

[0187] Referring to FIG. 17, the development roller 10dis provided with a development roller gear 15b, the position of which is on the outward side of the journal portion 10d1 in terms of the longitudinal direction. Referring to FIGS. 7, 13, and 22, the development roller gear 15bis meshed with the developing means driving gear 15a. The developing means driving gear 15ais integral with a developing means driving coupling 39, as the rotational driving force receiving member of the developing means, on the cartridge side. The developing means driving coupling 39 on the cartridge side is provided with a round hole, the axis of which coincides with the rotational axis of the developing means driving coupling 39 and the rotational axis of the developing means driving gear 15a. An unillustrated shaft with which the end plate 12hof the developing means frame 12 is provided, and which extends outward of the process cartridge B in terms of the longitudinal direction, fits in the aforementioned round hole of the developing means driving coupling 39 integral with the developing means driving gear 15a, allowing the developing means driving coupling 39 with the developing means driving gear 15ato freely rotate.

[0188] The developing means driving gear 15ais meshed with a smaller diameter gear 15c1 of a step gear 15c. The step gear 15cis rotatably fitted around a shaft 12pwhich is integral with the end plate 12hand extends outward in terms of the longitudinal direction from the end plate 12h.The larger diameter gear 15c2 of the step gear 15cis meshed with the stirring gear 15dattached to the rear end of the shaft of the stirring screw 10gillustrated in FIG. 2. The stirring gear 15dis meshed with the stirring gear 15eattached to the rear end of the shaft of the stirring screw 10h. The stirring gears 15dand 15eare provided with an unillustrated journal which projects from the center of each stirring gear. The end portion of the unillustrated journal of the stirring gear 15d(15e) is provided with an unillustrated connecting portion by which the journal is connected to the stirring screw 10g(10h). This connecting portion is also an integral part of the stirring gear (15e). The unillustrated journal of the stirring gear 15d(15e) is inserted into an unillustrated hole (with bearing surface) of the end plate 12hof the developing means frame 12, being rotatably supported by the end plate 12h, and the connecting portion is connected to the rear end of the shaft of the stirring screw 10g(10h) and drives the stirring screw 10g(10h).

[0189] The front end of the shaft of the stirring screw 10g(10h) is provided with a center hole. Referring to FIG. 14, the end plate 12iof the developing means frame 12, which is on the opposite side of the developing means frame 12 with respect to the aforementioned end plate 12hof the developing means frame 12, is provided with supporting shafts 19gand 19h, which are anchored, by press-fitting, in the holes made in the end plate 12i, perpendicular to the end plate 12i, and project inward of the developing means frame 12 in terms of the longitudinal direction. The inward end of the supporting shafts 19g(19h) is inserted into the aforementioned center holes of the front end of the shaft of the stirring screw 10g(10h), rotatably supporting the stirring screw 10g(10h). With the provision of the above structural arrangement, as the driving force is transmitted from the apparatus main assembly 14 to the process cartridge B in the apparatus main assembly 14, the developing means driving coupling 39 is rotated. As a result, the developing means driving gear 15aintegral with the developing means driving coupling 35 rotates the development roller gear 15b. Consequently, the development roller 10drotates. Further, the developing means driving gear 15adrives the stirring gear 15dthrough the step gear 15c, and the stirring gear 15dtransmits its rotation to the stirring gear 15e. As a result, the stirring screws 10gand 10hrotate and stir toner while circulating toner.

[0190] The aforementioned development roller 10dis made to rotate in the same direction as the photosensitive drum 7. Thus, in the area in which the distance between the peripheral surfaces of the development roller 10dand photosensitive drum 7 is smallest, that is, the development station, the two peripheral surfaces move in the opposite directions. Therefore, in the development station, the spacer rollers 10j(FIG. 17) rotatably fitted around the longitudinal ends of the development roller 10drotate in the same direction as the photosensitive drum 7 while rotating in the direction opposite to the rotational direction of the development roller 10d.

[0191] Referring to FIG. 21, the aforementioned gears 15a, 15b, 15c, 15d, and 15eare covered with the rear cover 17 directly fixed to the end plate 12hof the developing means frame 12.

[0192] (Driving of Charge Roller)

[0193] Referring to FIGS. 11, 23, and 24, the gear unit 24 fixed to the rear end portion of the charge unit C in terms of the longitudinal direction comprises a two piece gear case formed of gear case pieces 61 and 62, and a gear train 24G covered by the gear case pieces 61 and 62.

[0194] The gear case pieces 61 and 62 are constructed so that they become separable from each other in the longitudinal direction. The gear case piece 61 is placed in contact with the rear end portion of the charging means frame 13, and the gear case piece 62 is placed in contact with the gear case piece 61. Both pieces 61 and 62 are fixed to the charging means frame 13 with the use of small screws 58 put through both pieces 61 and 62.

[0195] FIG. 23 is a front view of the charge unit C, that is, a plan view of the rear end of charge unit C in terms of the direction in which the process cartridge B is inserted. FIG. 24 is an internal view of the charge unit C exposed at the planes indicated by the lines A-B-C-D-E in FIG. 23. The charging means driving coupling 38 on the cartridge side is provided with a step gear 24aintegral with the coupling 38. In the center hole 24a3 of the step gear 34a, a supporting shaft 61 a, which is fixed to the gear case piece 61 with the use of a small screw 63, and extends outward in the longitudinal direction, is rotatably fitted. Incidentally, the supporting shaft 61amay be integrally formed with the gear case piece 61. The charge roller 8ais rotatably supported by the charge roller bearing 20 on the rear side fitted in the component mounting portion 13fof the charging means frame 13. The large diameter gear portion 24a1 of the step gear 24ais meshed with a charge roller gear 24bfixed to one end of the charge roller 8a. In a hole 62bof the gear case piece 62, one end of the magnet 8bis supported. The large diameter gear portion 24a1 of the step gear 24aand the small diameter gear portion 24a2 of the step gear 24aare fixed to each other by press-fitting the latter into the former. However, the two gear portions 24a1 and 24a2 may be integrally formed.

[0196] (Process Cartridge Driving Apparatus)

[0197] The apparatus main assembly 14 is provided with a driving apparatus for driving the process cartridge B. This driving apparatus is a driving unit comprising three couplings: a coupling which couples with the photosensitive drum driving coupling 37don the cartridge side, a coupling which couples with the charging means driving coupling 38 on the cartridge side, and a coupling which couples with the developing means driving coupling 39 on the cartridge side. Incidentally, since the photosensitive drum driving apparatus illustrated in FIGS. 19 and 20 is different in configuration from that in this embodiment, the referential codes used in FIGS. 19 and 20 are not used for the description of this embodiment.

[0198] Each of the above described three couplings is driven by its own driving force source. As described previously, on the side of the coupling on the process cartridge side, the cartridge frame positioning portion and photosensitive drum positioning portion are placed on the same shaft, but apart from each other. Therefore, the photosensitive drum 7, the charge roller 8a, and the development roller 10dare not affected by the driving systems that do not belong to them, rendering this embodiment superior, in particular, in the smoothness of the rotation of the photosensitive drum 7 and the speed at which the apparatus starts up. Referring to FIG. 1, behind each of the process cartridges B (BK, BM, BC, and BB), different in toner color, and in the cartridge mounting space of its own in the apparatus main assembly 14, a driver unit is located. As the process cartridge B is inserted into the cartridge mounting space in the longitudinal direction (axial direction of photosensitive drum 7), each coupling as a driving force receiving member on the process cartridge side engages with its counterpart, or a coupling as the driving force transmitting member on the driving unit side.

[0199] FIG. 25 is a perspective view of the driving unit, and FIG. 26 is a front view of the driving unit in FIG. 25, with its front plate removed. FIG. 27 is a rear view of the same driving unit. In FIGS. 26 and 27, the gears are represented by only their pitch circles. FIG. 28 is a sectional view of the driving unit, exposed at the planes indicated by the line F-G-H-I-J-K-L in FIG. 27, and FIG. 29 is a sectional view of the driving unit, exposed at the planes indicated by the line N-O-P-Q-R-S in FIG. 27. FIG. 30 is a sectional view of the driving unit, exposed at the planes indicated by the line T-U-V-W-X-Y-Z in FIG. 27.

[0200] Referring to FIG. 26, the driving unit has three couplings: the photosensitive drum driving coupling 66, or the primary coupling, with a coupling hole 66a, with or from which the coupling projection 37don the process cartridge side is engaged or disengaged; the charging means driving coupling 67 with or from which the charging means driving coupling 38 on the process cartridge side is engaged or disengaged; and the developing means driving coupling 68 with or from which the developing means driving coupling 39 on the process cartridge side is engaged or disengaged. These couplings 66, 67, and 68 project frontward, that is, toward the direction from which the process cartridge B is inserted (front side with respect to the surface of the sheet on which FIG. 25 is drawn), from the front plate 65.

[0201] Referring to FIG. 27, on the outward side of the rear plate 69, there are a motor 71 as the driving power source for driving the photosensitive drum 7, a motor 72 as the driving power source for driving the charge roller 8a, and a motor 73 as the driving power source for driving the development roller 10d, which are fixed to the rear plate 69. The shaft of each of the motors 71, 72, and 73 extends between the front and rear plates 65 and 69. The motor 71 for driving the photosensitive drum 7 is a servo-motor, and its shaft extends rearward past the rear plate 69.

[0202] The front and rear plates 65 and 69, which are flat, are connected to each other with a plurality of stays 75 so that the front and rear plates 65 and 69 are held parallel to each other. Referring to FIGS. 28-30, one end of each stay 75 is fixed to the front plate 65 by a portion 75a, and with the use of swaging, and the other end is fixed to the front surface of the rear plate 69 with the use of a small screw 76 which is screwed into the stay 75, through the hole in the rear plate 69, from the backside of the rear plate 69. The front plate 65 is provided with a plurality of driving unit anchoring portions 65afor anchoring the driving unit E to the apparatus main assembly 14. These driving unit anchoring portions 65aare offset frontward from the front plate, by the same distance so that their offset surfaces remain in the same vertical plane. In this embodiment, the number of the driving unit anchoring portions 65ais four. The driving unit E is anchored to the apparatus main assembly 14 with the use of small screws (unillustrated).

[0203] Referring to FIG. 28, there is a gear train 74 between the photosensitive drum driving coupling 66 and the motor 71.

[0204] (Photosensitive Drum Driving Apparatus)

[0205] Also referring to FIG. 29, a coupling shaft 77 is supported by a bearing 78 fitted in a hole of the front plate 65, and a bearing 79 fitted in a hole of the rear plate 69. Around a shaft portion 77c, which has a D-shaped cross section, and is smaller in diameter than the flange portion 77aat the front end, the photosensitive drum driving coupling 66 on the main assembly side is fitted, in a manner to allow the coupling 66 to move freely in the shaft direction. Between the flange with which the bearing 78 is provided, and the photosensitive drum driving coupling 66 on the main assembly side, a compression coil spring 82 is fitted, in the compressed state, around the shaft portion 77cwith the D-shaped cross section, and therefore, the coupling 66 is kept in contact with the flange 77aat the front end of the shaft portion 77cwith the D-shaped cross section, by the pressure from the compression coil spring 82. The diameter of the shaft portion 77b, which is put through the bearing 78, is the same all the way from the front side to the rear end, but is smaller than the diameter of the shaft portion 77awith the D-shaped cross section, creating a stepped portion. This stepped portion is where the front surface of the bearing 78 is in contact, whereas the rear surface of the bearing 78 is in contact with the boss 74e3 of a large diameter gear 74e. The large diameter gear 74eis prevented from moving in the shaft direction, by a stopper ring 81 which contacts the large diameter gear 74e, on the side opposite to where the large diameter gear 74econtacts the bearing 78. The stopper ring is fitted in a circumferential groove of the shaft portion. In a key slot 74e2 cut in the large diameter gear 74e, a pin 83 put through the shaft portion 78e1 in the diameter direction is fitted, to assure that the large diameter gear 74efitted around the coupling shaft 74 rotates with the coupling shaft 77. The bearing 79 with a flange, which is inserted in the hole of the rear plate 69, is prevented from moving in the shaft direction, by a stopper ring 84 fitted in the circumferential groove of the shaft portion 77b. The coupling shaft 77 is provided with a detecting means for detecting the rotational angle of the coupling shaft 77, such as an encoder 85, which projects rearward from the rear plate 69. The detecting means is used for controlling the photosensitive drum 7.

[0206] A gear 74bmeshed with the pinion gear 74afixed to the output shaft of the motor 71 is meshed with the large diameter gear 74c1 of the step gear 74c. A gear 74dmeshed with the small diameter gear 74c2 of the step gear 74cis meshed with the large diameter gear 74e. The intermediary gears 74b, 74c, and 74dare rotatably fitted around the small diameter portions 86a, 87a, and 88a, of their own shafts 86, 87, and 88, correspondingly. These gears are prevented from moving in their shaft directions, except for a very slight distance, by the stepped portions between the large diameter portions 86b, 87b, and 88bof the shafts 86, 87, and 88, and the shaft portions 86a, 87a, and 88asmaller in diameter than the large diameter portion 86b, 87b, and 88a, and stopper rings 89, 91, and 92 fitted in the circumferential grooves of the smaller diameter portions 86a, 87a, and 88a, correspondingly. One end of each of the shafts 86, 87, and 88 is fixed in a hole of the front plate 65 by swaging, and the other end is simply fitted in the hole of the rear plate 69.

[0207] The gears 74a-74eare helical gears. The pinion gear 74ais a right-hand helix twist gear, and the large diameter gear 74eis also a right-hand helix twist gear.

[0208] Referring to FIG. 29, the gears 74a-74eare provided with flanges 74a1, 74b1, 74c3, 74c4, 74d1, and 74e1, correspondingly. The side surface of the flange of each gear is in contact with the side surface of the gear with which this gear is meshed. The position of the flange of each gear, with respect to the gear to which the flange is attached, is on the side opposite to the flange of the gear with which this gear is meshed, in terms of the shaft direction.

[0209] Each gear rotates in such a direction that its peripheral surface moves in the direction indicated by an arrow mark in FIG. 28. In other words, it rotates in such a direction that the photosensitive drum 7 rotates in the counterclockwise direction as shown in FIG. 1.

[0210] As the motor 71 rotates, the gear 74bmeshed with the gear 74aof the output shaft of the motor 71 is subjected to thrust which pushes it rightward in FIG. 29. The thrust is caught by the side surface 74b2 of the gear 74bas the side surface 74b2 of the gear 74bcomes into contact with, and slides on, the flange 74a1 integral with the pinion gear 74a, and/or the flange 74c3 of the large diameter gear 74c1 of the step gear 74c; by the flange 74bof the gear 74band the side surface 74a2 of the pinion gear 74aof the motor shaft; and/or by the flange 74b1 as it comes into contact with the side surface 74c6 of the large diameter gear 74c1 of the step gear 74c. All that is necessary is for the thrust to be caught by one of the above listed portions. In consideration of manufacture errors, the number of the portions which catch the thrust may be only one.

[0211] The directions in which the large diameter gear 74c1 and small diameter gear 74c2 of the step gear 74care twisted are the same, and are subjected to thrust that pushes them leftward in FIG. 29. This thrust is caught by the side surface 74b2 of the gear 74bas the flange 74c3 of the large diameter gear 74c1 of the step gear 74ccomes into contact with the side surface 74b2 of the gear 74b; by the side surface 74d2 of the gear 74d, as the flange 74c4 of the small diameter gear 74c2 comes into contact with the side surface 74d2 of the gear 74d; by the flange 74d1, as the side surface 74c5 of the small diameter gear 74c2 comes into contact with the flange 74d1; and/or by the flange 74b1 of the gear 74b, as the side surface 74c7 of the large diameter gear 74c1 comes into contact with the flange 74b1 of the gear 74b. In other words, this thrust is caught by at least one of the above listed portions.

[0212] The thrust from the gear 74dapplies rightward in FIG. 29, and is caught by the contact between the flange 74d1 and the side surface 74c5 of the small diameter gear 74c2 of the step gear 74c, the contact between the side surface 74d2 of the gear 74dand the flange 74c4 of the small diameter gear 74c2 of the step gear 74c, the contact between the side surface 74d2 of the gear 74dand the flange 74e1 of the large diameter gear 74e, and/or the contact between the flange 74d1 and the side surface 74e4 of the large diameter gear 74e. In other words, this thrust is caught by any one or more among the above listed contacts. As described before, the large diameter gear 74eis mounted on the coupling shaft 77 in such a manner that it does not move in the shaft direction.

[0213] Further, the positions of the intermediary gears 74b, 74c, and 74din terms of the shaft direction are fixed by the stepped portion between the large diameter portions 86b, 87b, and 88bof the shafts 86, 87, and 88, and the small diameter portions 86a, 87a, and 88aof the shaft 86, 87, and 88, and also by the stopper rings 89, 91, and 92, correspondingly. Therefore, the thrust upon the intermediary gears 74band 74dis blocked by the stopper rings 89 and 90, respectively, and the thrust upon the intermediary gear 74cis blocked by the stepped portion of the shaft 87.

[0214] With the provision of the above-described structural arrangement, the position of the pinion gear 74aof the motor shaft, and the position of the large diameter gear 74eon the coupling shaft 77, relative to their own shafts, with respect to the shaft direction, are fixed by their own shafts. However, the positions of the pinion gear 74aof the motor shaft, large diameter gear 74eon the coupling shaft 77, and intermediary gears 74b, 74c, and 74d, with respect to the shaft direction, are controlled by the contacts between their flanges and the side surfaces of the pertinent gears, and therefore, the intermediary gears 74b, 74c, and 74dare afforded a slight movement in their shaft directions.

[0215] (Charge Roller Driving Apparatus)

[0216] FIG. 30 shows the charging means driving apparatus portion of the apparatus main assembly 14, equipped with a coupling which can be engaged with or disengaged from the charging means driving coupling 38 on the cartridge side. The charging means driving coupling 67 on the main assembly side (driving side) is mounted on the shaft, which aligns with the shaft of the charging means coupling 38 on the process cartridge side as the process cartridge B is inserted into the apparatus main assembly 14. It is mounted on the shaft in such a manner that as the process cartridge B is inserted into, or removed from, the apparatus main assembly 14, it engages with, or disengages from, the charging means coupling 38 on the process cartridge side. These couplings are in the form of one side of a claw (tooth) clutch; in other words, their coupling portions are provided with a pair of teeth (ridges) and a pair of gaps (valleys), being enabled to lock themselves with their counterparts to transmit a rotational force. The charging means coupling 67 on the main assembly side is mounted on a coupling shaft 93 in such a manner that it is movable in the direction of the coupling shaft 93. The coupling shaft 93 is rotatably supported by an unillustrated bearing fitted in a bracket 90 fixed to the front plate 65, being allowed to move in its axial direction. A portion 93aof the coupling shaft 93, around which this coupling 67 is fitted, has a D-shaped cross section. This shaft portion 93awith the D-shaped cross section fits into the D-shaped hole of the coupling 67, and therefore, the coupling shaft 93 and coupling 67 rotate together. The two circumferential grooves of the coupling shaft 93, one at the front end of the coupling 93 and the other immediately behind the front plate 65, are fitted with stopper rings 94 and 95, respectively. Between the coupling 67 and bracket 90, a compression coil spring 96 is fitted, in the compressed state, around the coupling shaft 93.

[0217] A pinion gear 98afixed to the shaft of the motor 72 fixed to the rear plate 69 is meshed with the large diameter gear 98b1 of a step bear 98b, and the gear 98cmeshed with the small diameter gear 98b2 of the step gear 98bis meshed with a gear 98dfixed to the rear end of the coupling shaft 93. The rear end portion 93cof the coupling shaft 93 is reduced in diameter, creating a step 93b. The cross section of this rear end portion 93cis D-shaped. The gear 98dis prevented from moving on the coupling shaft 93 in the shaft direction, by this step 93b, and a stopper ring 99 fitted in the circumferential groove with which the shaft portion 93cwith the D-shaped cross section is provided. In order to assure that the gears 98cand 98dremain always meshed with each other, in spite of the fact that the gear 98dis allowed to move with the coupling shaft 93, a certain distance in the shaft direction, the face width of the gear 98cis rendered greater than that of the gear 98d.

[0218] One side of the step gear 98bis rotatably supported by the reduced diameter portion 111aof the shaft 111, one end of which is fixed to the front plate 65 by swaging, and the other end of which is simply fitted in a hole of the rear plate 69. The step gear 98bis prevented from moving on the nonrotational shaft 111 in the shaft direction, by a step 111cbetween the larger diameter portion 111band reduced diameter portion 111aof the nonrotational shaft 111, and the stopper ring 100 fitted in the circumferential groove of the reduced diameter portion 111a. The pinion gear 98aand the large diameter gear 98b1 of the step gear 98bare helical gears.

[0219] The gear 98cis fitted around the reduced diameter portion 112aof a nonrotational shaft 112, one end of which is inserted in the hole of the front plate 65 and fixed thereto by swaging. The movement of the gear 98cin the shaft direction is controlled by a step 112cbetween the larger diameter portion 112band reduced diameter portion 112aof the nonrotational shaft 112, and a stopper ring 110 fitted in the circumferential groove of the reduced diameter portion.

[0220] (Development Roller Driving Apparatus)

[0221] FIG. 31 shows a development roller driving apparatus portion of the image forming apparatus, on the main assembly side. On a shaft in alignment with the shaft of the developing means driving coupling 39 on the process cartridge side, a developing means driving coupling 68 on the apparatus main assembly side, is mounted in such a manner that the two couplings can be engaged or disengaged. This pair of couplings constitute a claw (tooth) type clutch; in other words, the coupling surface of each coupling is provided with a pair of teeth (ridges) and a pair of tooth gaps (valleys), which lock with those of the counterpart to transmit a rotational force.

[0222] The developing means driving coupling 68 on the apparatus main assembly side is mounted on a coupling shaft 115, being allowed to move in the shaft direction. The coupling shaft 115 is rotatably borne by an unillustrated bearing fitted in a hole of a bracket 114 fixed to the front plate 65, being enabled to move in its longitudinal direction. The portion 115aof the coupling shaft 115 around which the developing means driving coupling 68 on the main assembly side is fitted is given a D-shaped cross section; the shaft portion 115awith the D-shaped cross section fits in the D-shaped hole of the aforementioned coupling 68 so that the coupling 68 and coupling shaft 115 rotate together. The coupling shaft 115 is provided with two circumferential grooves, one being at the front end and the other being immediately behind the front plate 65, and the front groove is fitted with a stopper ring 116 and the rear groove is fitted with a stopper ring 117. Between the developing means driving coupling 68 on the apparatus main assembly side and the bracket 114, a compression coil spring 118 is fitted, in the compressed state, around the coupling shaft 115.

[0223] With the pinion gear 121afixed to the motor shaft of the motor 73 fixed to the rear plate 69, the large diameter gear 121c1 of a step gear 121cis engaged, with the interposition of a gear 121b. A gear 121d, meshed with the smaller diameter gear 121c2 of the step gear 121c1, is meshed with a gear 121efixed to the rear end of the coupling shaft 115. The rear end portion 115bof the coupling shaft 115 is reduced in diameter, creating a step 115c. This reduced diameter shaft portion 115bis given a D-shaped cross section. The gear 121eis prevented from moving in the shaft direction, by this step 115c, and a stopper ring 122 fitted in a circumferential groove with which the reduced shaft portion 115bwith the D-shaped cross section is provided.

[0224] The gear 121b, the step gear 121c, and the gear 121dare rotatably supported by the reduced diameter portions 123a, 124a, and 125aof their own nonrotational shafts 123, 124, and 125, which are fixed, by one end, to the front plate 65 by swaging, and are fitted, by the other end, in the holes of the rear plate 69, correspondingly. The gears 121b, 121c, and 121dare prevented from moving in the shaft direction, by the steps 123c, 124c, and 125cbetween the larger diameter portions 123b, 124b, and 125band reduced diameter portions 123a, 124a, and 125bof the nonrotational shafts 123, 124, and 125, and the stopper rings 126, 127, and 128 fitted in the circumferential grooves of the reduced diameter portion 123a, 124a, and 125a, correspondingly. The pinion gear 121 a, gear 121b, and larger diameter gear 121c1 of the step gear 121care helical gears.

[0225] As described above, the driving apparatus E with which the apparatus main assembly 14 is provided to drive the process cartridge B comprises: the photosensitive drum driving coupling 66, charging means driving coupling 67, and developing means driving coupling 68. These couplings are independently driven by their own motors, that is, the photosensitive drum driving motor 71, the charging roller driving motor 72, and the development roller driving motor 73, through their own gear trains. In other words, the rotation of the photosensitive drum 7 is not linked to the rotation of the charge roller 8a, the development roller 10d, the stirring screws 10gand 10h, and the like, and therefore, the photosensitive drum 7 is not affected by the changes in the load which applies to the stirring screws 10gand 10h, and the like. Further, during the period in which the photosensitive drum 7 is started up, the photosensitive drum 7 is not subjected to the stirring load of the stirring screws 10gand 10h, as well as the inertia load of the charge roller 8aand the development roller 10d, and the gear trains connecting the development roller 10d, the stirring screws 10gand 10, and the photosensitive drum 7. Therefore, the photosensitive drum 7 is smaller in the change in its rotational velocity, and also faster in its startup.

[0226] As the process cartridge B is inserted into the apparatus main assembly 14 in the longitudinal direction, the coupling 37d(cartridge side coupling) of the drum flange 37 integral with the photosensitive drum 7 engages into the coupling hole 66aof the above described driving unit E with which the apparatus main assembly 14 is provided. When the engagement does not occur, the photosensitive drum driving coupling 66 on the apparatus main assembly side is pushed back (moved rightward) on the coupling shaft 77 in the shaft direction in FIG. 28, against the force from the compression coil spring 82. In this state, the coupling surfaces of the coupling 37dand 66aare in contact with each other, without fully engaging, due to the pressure from the compression coil spring 82. Thus, as soon as the cartridge side coupling 37dand coupling hole 66aon the apparatus main assembly side coincide in rotational phase as the motor 71 rotates, the coupling 66 is caused to slide on the coupling shaft 77, by the force from the compression coil spring 82. As a result, the cartridge side coupling 37dengages into the coupling hole 6aon the apparatus main assembly side. In this state, the position of the coupling 66 on the driving side with respect to the shaft direction is fixed by the contact between the coupling 66 and the flange 77alocated at the tip of the coupling shaft 77. The cartridge side coupling 37d, and the coupling hole 66aon the apparatus main assembly side, are in the form of a twisted equilateral triangular pillar, and are configured so that they loosely fit with each other; in other words, the longitudinal ridges of the cartridge side coupling 37din the form of a twisted equilateral triangular pillar make contact with the walls of the coupling hole 66ain the form of a twisted equilateral triangular pillar, one for one. Thus, as the main assembly side coupling 66 rotates, such force that causes the two couplings to pull each other while aligning the rotational axes of the cartridge side coupling 37dand the main assembly side coupling 66 relative to each other. As a result, the cartridge side coupling 37dengages into the coupling hole 66aon the main assembly side, until the leading end of the coupling 37din the form of a projection contacts the tip of the coupling shaft 77 where the flange 77ais present. The position of the coupling shaft 77 as a driving shaft, relative to the driving unit E fixed to the apparatus main assembly 14, with respect to the shaft direction, is fixed, and therefore, as the cartridge side coupling 37dcomes into contact with the coupling shaft 77, the position of the photosensitive drum 7 relative to the apparatus main assembly 14 in terms of the shaft direction becomes fixed.

[0227] Incidentally, the coupling shaft 77 is pulled leftward in FIG. 28 as the projection of the cartridge side coupling 37dand the coupling portion with the hole 66apull each other. However, the boss 74e3 of the large diameter gear 74ecomes into contact with the bearing 78 with a flange, the position of which relative to the front plate 65 is fixed, and therefore, the stopper ring 81 comes into contact with the large gear 74e.

[0228] As the process cartridge B is inserted into the apparatus main assembly 14, the cartridge side coupling 37dengages into the coupling hole 66a. At the same time as the occurrence of this engagement, the charging means driving coupling 38 on the cartridge side, and the developing means driving coupling 39 on the cartridge side, engage with the charging means driving coupling 67 on the main assembly side and the developing means driving coupling 68, respectively. During these engagements, the couplings 38 and 67, which face each other, and the couplings 39 and 68, which face each other, engage with each other, as soon as the positions of their teeth align with the positions of the tooth gaps of their counterparts. When the teeth of one coupling 38 meet the teeth of the counterpart, the charging means driving coupling 38 and developing means driving coupling 39 on the cartridge side slide back the charging means driving coupling 67 and developing means coupling 68 on the apparatus main assembly side, on the coupling shafts 93 and 115, against the compression coil springs 96 and 118, respectively. Then, as the charging means driving coupling 67 and developing means driving coupling 98 on the apparatus main assembly side are rotated by the charge roller driving motor 72 and the development roller driving motor 73, the relationships in rotational phase between the coupling 38 and 67, and between the couplings 39 and 68, change until they match. Then, as soon as they match, the couplings 67 and 68 are caused to slide forward on the portions 93aof the shaft 93, and the portion 115aof the shaft 115, by the force from the compression springs 96 and 118, respectively. As a result, the couplings 67 and 68 engage with the couplings 38 and 39, respectively.

[0229] As the photosensitive drum driving motor 71 rotates, the rotation of the motor 71 is transmitted through the pinion gear 74a, the gear 74b, the step gear 74c, the gear 74d, the large diameter gear 74e, and coupling shaft 77 in this order. As a result, the main assembly side coupling 66 with the coupling hole 66arotates, and then, the rotational force is transmitted to the cartridge side coupling 37dfrom the coupling hole 66a, rotating the photosensitive drum 7.

[0230] In the description given above, the positional relationship among the intermediary gears for driving the photosensitive drum 7, in the driving unit E, with respect to the direction parallel to their shafts, is determined by the positions of their side surfaces and flanges. As described before, the pinion gear 74aand large diameter gear 74eare supported in such a manner that they do not move in their shaft directions. Referring to FIG. 29, the gears 74band 74dare subjected to rightward thrust, and the step gear 74cis subjected to the leftward thrust. However, they catch these thrusts, which they mutually effect, by their flanges and side surfaces. Therefore, the positions of the gears 74b, 74c, and 74din terms of their shaft directions are fixed in terms of their positional relationship among themselves, as well as relative to the pinion gear 74eand large gear 74e. During the process in which their positions become fixed, each gear could come into contact with the side surfaces of the flanges of adjacent gears, by a plurality of portions. However, the occurrence of contact between any one of the aforementioned plurality of the portions of each gear with the corresponding portion of an adjacent gear prevents the occurrence of contact between the rest of the portions of this gear with the corresponding portions of the adjacent gear. In other words, the gears 74b, 74c, and 74dare fitted on the nonrotational shafts 86, 87, and 88, between the steps between the large diameter portions 86b, 87b, and 88band reduced diameter portions 86a, 87a, and 88aof the nonrotational shafts 86, 87, and 88, and the stopper rings 89, 91, and 92, with the provision of a certain amount of play in the shaft direction, making it unnecessary for the positions of these gears with respect to the shaft direction to be precisely fixed.

[0231] (Relationship Between Maintenance of Constant Distance Between the Development Roller and the Photosensitive Drum, and the Development Means Driving Gear)

[0232] FIG. 31 shows the transmission of the rotational force from the developing driving coupling to the development roller, in terms of the load which applies to the components in the gear train between developing means driving coupling and the development roller.

[0233] The development roller 10dis fitted with a pair of spacer rings 10j, the diameters of which are greater than that of the development roller 10dby an amount equivalent to the development gap (shortest distance between peripheral surfaces of the photosensitive drum 7 and the development roller 10din the development station), and which are placed in contact with the peripheral surface of the photosensitive drum 7, so that the aforementioned development gap is provided between the photosensitive drum 7 and development roller 10d.

[0234] As described before, the photosensitive drum 7 and the development roller 10drotate in the same direction, and therefore, in the development station and the portions outside the development station in the longitudinal direction, their peripheral surfaces move in the opposite directions. Both longitudinal ends of the development roller 10dare provided with a journal portion 10d1, and the spacer ring 10jis rotatably fitted around the inward side of the journal portion 10d1, in terms of the longitudinal direction, with the rotational axis of the spacer ring 10jbeing in alignment with that of the journal portion 10d1. As described previously with reference to FIG. 18, the journal portion 10d1 is rotatably fitted in the hole 32awith a bearing surface, of the pivotal arm 32 pivotable about the pressure application center Slv. The pivotal arm 32 is kept under the pressure from the compression coil spring 35 so that the spacer ring 10jis kept pressed upon the photosensitive drum 7, outside the development station in terms of the longitudinal direction. Thus, in the area where the distance between the photosensitive drum 7 and the development roller 10dis smallest, as the photosensitive drum 7 and the development roller 10drotate, the spacer ring 10jfollows the rotation of the photosensitive drum 7, moving in the direction opposite to the movement of the peripheral surface of the development roller 10d.

[0235] Referring to FIG. 31, as the developing means driving coupling 39 receives a rotational force from the coupling 68 of the driving unit of the apparatus main assembly 14, the developing means driving coupling 39 and the driving gear 15arotate in the counterclockwise direction, and the rotation is transmitted from the driving gear 15ato the development roller gear 15b, causing the development roller 10dto rotate in the clockwise direction.

[0236] In this embodiment, all gears have involute teeth. Therefore, the transverse line of action of a tooth load F coincides with a straight line slanted relative to the line tangential to the pitch circles, inclusive of the pitch point T, of the gear 15aand 15b, by only the pressure angle.

[0237] The effect of the tooth load upon the contact pressure between the spacer ring 10jand photosensitive drum 7 can be reduced by placing them approximately in a horizontal orientation so that the angle formed by the above described transverse line of action of the tooth load, and the line connecting the center of the hole with a bearing surface, of the pivotal arm as the development roller supporting member, and the pivotal center Slv remains within a range of +30°. Therefore, such an arrangement makes it possible to reduce the force necessary to be applied by the compression coil spring 35 through the pivotal arm 32, which in turn makes it possible to reduce the amount of the contact pressure which works between the spacer ring 10jand the photosensitive drum when the process cartridge B is not in use. Consequently, the spacer ring 10jcan be prevented from creeping.

[0238] (Pressure Which Works Between the Charge Roller and the Photosensitive Drum)

[0239] FIG. 32 shows the load relationship when the rotational force is transmitted from the charging means couple to the charging unit which has the charge roller.

[0240] A gap is provided between the peripheral surfaces of the photosensitive drum 7 and the charge roller 8a. This gap is provided for a magnetic brush based charging process, in which not only is the photosensitive drum 7 charged, but also the transfer residual toner, or the toner remaining on the photosensitive drum 7 after image transfer, is taken in by the charge roller side, and sent back onto the photosensitive drum 7 after the polarity and potential level of the transfer residual toner are rectified. In order to create this gap, a pair of spacer rings 8nare rotatably fitted around a pair of the journal portions 8a2 of the charge roller 8a, one for one. The radius of each space ring 8nis greater than that of the charge roller 8aby an amount equivalent to the gap between the photosensitive drum 7 and charge roller 8a. The spacer rings 8nare kept in contact with the peripheral surface of the photosensitive drum 7, outside the charge station in terms of the longitudinal direction, by the pressure from unillustrated source and structural arrangement.

[0241] The photosensitive drum 7 and charge roller 8arotate in the same direction. Thus, in the charge station, and the areas outside the charge station in terms of the longitudinal direction, the peripheral surfaces of the photosensitive drum 7 and charge roller 8amove in the opposite directions. Representing the centers of the charge roller 8aand charging means driving coupling 38 by o3 and o4, respectively, an angle θ which is formed by the line connecting the center o1 of the photosensitive drum 7 and the center of the charge roller 8a, and the line connecting the center o3 of the charge roller 8aand the center o4 of the charging means driving coupling 38, is a right angle. Incidentally, this angle θ has only to be an approximately right angle. Further, all that is necessary is that a configurational arrangement is made so that, the torque T transmitted to the charging means coupling 38 from the coupling 67 of the driving unit of the apparatus main assembly 14 presses the charge roller 8aupon the photosensitive drum 7, except for the angle range in which, as the angle θ increases and approaches 180°, the charge roller 8ais subjected to the force directed toward the photosensitive drum 7 due to the wedging function. In FIG. 32, the center o3 of the charge roller 8amust be on the left side of the line connecting the center o4 of the charging means coupling 38 and the center o1 of the photosensitive drum 7.

[0242] Because of the torque T which the charging means couple 38 receives, the charging unit C is pressured to rotate in the counterclockwise direction about the center of the cylindrical shaft portion 26aby which the charging unit C is supported, and the hole 23a(FIG. 11). Thus, representing the distance between the center o3 of the charge roller 8aand the center o4 of the charging means driving coupling portion 38 by J, a contact pressure of T/J is generated between the spacer ring 8nof the charge roller 8aand the photosensitive drum 7.

[0243] On the other hand, representing the distance between the center line of the compression coil spring 30 and the center o4 of the charging means driving coupling 38 by L, a torque of Fs·L, Fs being the force generated by the compression coil spring 30, is generated in the adjacencies of the cylindrical shaft portion 26aand the hole 23a. By this torque, a contact pressure of Fs·L/J is generated between the spacer ring 8nof the charge roller 8aand the photosensitive drum 7.

[0244] With the provision of the above described structural arrangement, even if the force which the compression coil spring 30 generates for pressing the charging unit C is relatively small, a sufficient amount of contact pressure is generated and maintained between the spacer ring 8nand the photosensitive drum 7 during an image forming operation. Therefore, it is possible to employ a compression coil spring with a smaller amount of resiliency, which in turn makes it possible to make the contact pressure, generated between the spacer ring 8nand the photosensitive drum 7 by the compression coil spring when the process cartridge B is not in use, small enough to prevent the spacer ring 8nfrom creeping due to the contact pressure.

[0245] (Cartridge Chamber Unit)

[0246] FIG. 34 shows one of the cartridge chamber unit. Each image forming portion is provided with a cartridge chamber unit 14aas shown in FIG. 34. This cartridge chamber unit 14aincludes a cartridge guide 14band the driving unit E. The cartridge guide 14bhas a pair of guides 14c, which are perpendicular to the direction in which the recording medium 2 is conveyed, and are parallel to the surface of the recording medium 2. When the process cartridge B is inserted into, or removed from, the cartridge installation box 14a, the guide portions 12aand 29bof the process cartridge B are fitted into the pair of guides 14c. As the process cartridge B is inserted into the cartridge chamber unit 14a, the photosensitive drum driving coupling 37d(male coupling), charging means driving coupling 38, and developing means driving coupling 39, of the process cartridge B engage with couplings 66, 67, and 68 of the driving unit E.

[0247] With the provision of the above described cartridge chamber unit, the apparatus main assembly can be simplified with regard to the structure for transmitting the driving force to each of a plurality of process cartridges from its own driving force providing source.

[0248] The present invention could further improve the rotational accuracy of an electrophotographic photosensitive drum. Further, the present invention makes it possible to more accurately position an electrophotographic photosensitive drum relative to the main assembly of an image forming apparatus when a process cartridge is installed into the apparatus main assembly.

[0249] Further, the present invention makes it possible to position an electrophotographic photosensitive drum and a cartridge frame, independently from each other, relative to the main assembly of an image forming apparatus, when a process cartridge is installed into the main assembly of an image forming apparatus.

[0250] While the invention has been described with reference to the structures disclosed herein. it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.