Abstract:
A coupling pin for coupling a first frame and a second frame of a process cartridge detachably mountable relative to a main assembly of an electrophotographic image forming apparatus includes (a) a first shaft portion for being press-fitted into a first hole formed in the first frame; and (b) a second shaft portion for being press-fitted into a second hole formed in the first frame, where the second shaft portion is upstream of the first shaft portion in a direction of press-fitting of the coupling pin. The second shaft portion has an outer diameter which is larger than that of the first shaft portion. The pin further includes (c) a third shaft portion for being loosely fitted into a hole formed in the second frame with a gap between the third shaft portion and inside surface of the hole of the second shaft.

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a connecting pin that is used in a process cartridge removably installable in an electrophotographic image forming apparatus, and the process cartridge. In this specification, electrophotographic image forming apparatus refers to an apparatus which forms an image on recording medium with the use of an electrophotographic image forming system. It includes an electrophotographic copying machine, an electrophotographic printer (laser beam printer, LED printer, or the like), a facsimile machine, a word processor, and the like. 
     The term a “process cartridge” refers to a cartridge that is rendered removably installable in the main assembly of an electrophotographic image forming apparatus, and integrally comprises an electrophotographic photosensitive member, and at least one of three means: a charging means for charging an electrophotographic photosensitive member; a developing means for developing a latent image formed on the peripheral surface of the electrophotographic photosensitive member; and a cleaning means for removing the developer remaining on the peripheral surface of the electrophotographic photosensitive member. 
     In some of the image forming apparatuses which employ an electrophotographic photosensitive image forming system, a process cartridge system is employed. In the case of this type of process cartridge system, an electrophotographic photosensitive member, and one or more processing means, which work with the electrophotographic photosensitive member, are integrally placed in a cartridge. With the employment of this type of process cartridge system, the image forming apparatus can be maintained by a user himself, without the need for relying on service personnel, and therefore, the usability of the apparatus is greatly improved. 
     A typical structure of such a process cartridge comprises two frames, for example, a cleaning unit frame and an image developing unit frame, which are connected to each other. The cleaning unit frame contains an electrophotographic photosensitive drum, a charging device, and a cleaning device, and the image developing unit frame comprises an image developing means frame and a toner frame. The developing means frame supports a developing means, and the toner frame constitutes a toner chamber. The cleaning unit frame, and the image developing unit frame are connected in such a manner that the two frames are rendered pivotable about a connecting pin (axis). Further, the two frames are kept under such force that is generated with the use of an elastic member, for example, a spring, and that maintains a predetermined positional relationship between the photosensitive drum and the developing means. This two piece structure has various functional advantages and merits. For example, the two piece structure makes it easier to keep the pressure applied upon the photosensitive drum by an image developing roller, at a proper level, and it is also easier to maintain the proper gap between the peripheral surfaces of the photosensitive drum and the image developing roller. Further, the two piece structure makes it easier to mold the structural components of the process cartridge, and also to assemble the components into the process cartridge. 
     SUMMARY OF THE INVENTION 
     Accordingly, the primary object of the present invention is to provide a connecting pin which assures that the two frames of a process cartridge are properly connected. 
     Another object of the present invention is to provide a connecting pin which does not easily disengage from the frames of a process cartridge. 
     Another object of the present invention is to provide a coupling pin for coupling a first frame and a second frame of a process cartridge detachably mountable relative to a main assembly of an electrophotographic image forming apparatus, comprising: (a) a first shaft portion for being press-fitted into a first hole formed in the first frame; (b) a second shaft portion for being press-fitted into a second hole formed in the first frame, wherein the second shaft portion is upstream of the first shaft portion in a direction of press-fitting of the coupling pin, and the second shaft portion has an outer diameter which is larger than that of the first shaft portion; and (c) a third shaft portion for being loosely fitted into a hole formed in the second frame with a gap between the third shaft portion and inside surface of the hole of the second shaft. 
     Another object of the present invention is to provide a process cartridge that comprises two frames connected with the connecting pin described above. 
     These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a horizontal section of the joint between the two frames of a process cartridge, and the areas adjacent thereof, in the first embodiment of the present invention. 
     FIG. 2 is a vertical section of the joint between the two frames of a process cartridge, and the areas adjacent thereof, depicting the essential structure thereof, in the first embodiment of the present invention. 
     FIG. 3 is a vertical section of a typical image forming apparatus in accordance with the present invention. 
     FIG. 4 is an external perspective view of a typical image forming apparatus in accordance with the present invention. 
     FIG. 5 is a vertical section of a typical process cartridge in accordance with the present invention. 
     FIG. 6 is a perspective view of a cleaning unit in accordance with the present invention. 
     FIG. 7 is a perspective view of an image developing unit in accordance with the present invention. 
     FIG. 8 is a horizontal section of the joint between the two frames of a process cartridge, and the areas adjacent thereof, in the first embodiment of the present invention. 
     FIG. 9 is a horizontal section of the joint between the two frames of a process cartridge, and the areas adjacent thereof, in the second embodiment of the present invention. 
     FIG. 10 is a horizontal section of the joint between the two frames of a process cartridge, in the third embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     Hereinafter, the desirable embodiments of the present invention will be described in detail with reference to the drawings. 
     In the following embodiments of the present invention, the “widthwise” direction of a process cartridge B means the direction in which a process cartridge is inserted into, or removed from, the main assembly  14  of an image forming apparatus, and this direction coincides with the direction in which recording medium is conveyed. The “lengthwise” direction of the process cartridge B means the direction which intersects, horizontally and substantially perpendicularly, the direction in which the process cartridge B is inserted into, or removed from, the main assembly  14 , and this direction is parallel to the surface of the recording medium, and also intersects, substantially perpendicularly, the direction in which the recording medium is conveyed. The “left-hand side or right-hand side” of the process cartridge B means the left-hand or right-hand side of the process cartridge B as seen from above and behind, in relation to the recording medium which is being conveyed. 
     FIG. 3 is a drawing which depicts the structure of an electrophotographic image forming apparatus (laser beam printer) in accordance with the present invention, and FIG. 4 is an external perspective view of the apparatus in FIG. 3 FIGS. 4-7 are also drawings related to the process cartridges in accordance with the present invention. In the following description of the embodiments of the present invention, the top side of the process cartridge B means the side that faces upward when the process cartridge B is in the main assembly  14  of the image forming apparatus, and the bottom side of the process cartridge B means the side that faces downward when the process cartridge B is in the main assembly  14 . 
     Electrophotographic Image Forming Apparatus A and Process Cartridge B 
     First, referring to FIGS. 3 and 4, a laser beam printer A as an electrophotographic image forming apparatus in accordance with the present invention will be described. FIG. 5 is a vertical cross section of the process cartridge B. 
     Referring to FIG. 3, this laser beam printer A is a printer which forms an image on a piece of recording medium (recording sheet, OHP sheet, fabric, or the like) through an electrophotographic image forming process; it forms a toner image on an electrophotographic photosensitive member in the form of a drum (hereinafter, “photosensitive drum”). More specifically, the photosensitive drum is charged by a charging means, and a laser beam modulated with image forming data is projected onto the charged photosensitive drum from an optical means, and as a result, a latent image reflecting the image forming data is formed on the photosensitive drum. The latent image is developed into a toner image by a developing means. While the latent image is formed, the recording medium  2  placed in a sheet feeder cassette  3   a  are fed out of the cassette  3   a,  one by one. Then, the recording medium  2  is conveyed to the interface between the photosensitive drum and an image transferring roller  4  as an image transferring means, by conveyer roller pairs  3   c  and  3   d,  and a sheet registering roller pair  3   e,  in such a manner that the recording medium surface facing downward in the cassette  3   a  turns to face upward in the interface, and such that the recording medium arrives at the interface in synchronism with the toner image. Next, the toner image formed on the peripheral surface of the photosensitive drum  7  of the process cartridge B is transferred onto the recording medium  2  by applying electrical voltage to the image transferring roller  4 . The recording medium  2  on which the toner image has been transferred is conveyed to a fixing means  5  by a recording medium conveying guide  3   f.  The fixing means  5  comprises a driving roller  5   c,  and an image fixing roller  5   b  which contains a heater  5   a.  The fixing means  5  fixes the toner image having been transferred onto the recording medium  2 , to the recording medium  2  by applying heat and pressure to the recording medium  2  and the toner image. Thereafter, the recording medium  2  is conveyed through a turnover path by discharging roller pairs  3   g  and  3   h,  and is discharged into a delivery tray  6  by a discharge roller pair  3   i.  The delivery tray  6  is on the top side of the main assembly  14  of an image forming apparatus A. It should be noted here that a pivotable flapper  3   k  may be operated to discharge the recording medium  2  from the main assembly  14 , without conveying the recording medium  2  through the turnover path. In this embodiment, the pickup roller  3   b,  conveying roller pairs  3   c  and  3   d,  registering roller  3   e,  conveying guide  3   f,  discharging roller pairs  3   g,    3   h,  and  3   i,  and discharge roller pair  3   m  constitute a recording medium conveying means  3 . 
     Referring to FIGS. 3 and 5, in the process cartridge B, the peripheral surface of the photosensitive drum  7  is uniformly charged by applying electrical voltage to a charging roller  8 , as a charging means, while rotating the photosensitive drum  7 . Next, a laser beam modulated with the image forming data is projected through an exposure opening  1   e  onto the uniformly charged peripheral surface of the photosensitive drum  7 , and as a result, a latent image is formed on the peripheral surface of the photosensitive drum  7 . Then, the latent image is developed with the use of toner and an image developing means  9 . The charging roller  8  is disposed in contact with the photosensitive drum  7  to charge the photosensitive drum  7 . The charging roller  8  is rotated by the rotation of the photosensitive drum  7 . The image developing means  9  develops the latent image formed on the peripheral surface of the photosensitive drum  7 , by supplying the peripheral surface of the photosensitive drum  7  with toner. The optical system  1  comprises a laser diode  1   a,  a polygon mirror  1   b,  a lens  1   c,  and a deflection mirror  1   d.    
     As for the operation of the image developing means  9 , a toner feeding means  9   b  is rotated to feed the toner within a toner container  11 A, to an image developing roller  9   c  which is being rotated, and in which a magnet is fixedly disposed. As a result, a layer of toner triboelectrically charged by a toner regulating blade  9   d  is formed on the peripheral surface of the image developing roller  9   c.  As the image developing roller  9   c  is further rotated, the layer of triboelectrically charged toner enters the image developing zone, that is, the interface between the image developing roller  9   c  and the photosensitive drum  7 , in which triboelectrically charged toner particles are transferred from the toner layer to the peripheral surface of the photosensitive drum  7  in a manner to reflect the latent image having been formed on the peripheral surface of the photosensitive drum  7 ; the latent image is developed, or visualized, into a toner image. As for the regulating blade  9   d,  it regulates the amount by which the toner is coated on the peripheral surface of the image developing roller  9   c,  and at the same time, triboelectrically charges the toner particles being coated on the image developing roller  9   c.  Adjacent to the image developing roller  9   c,  a stirring member  9   e  is rotatively disposed, which circulates the toner particles in the developer (toner) container. 
     The toner image formed on the photosensitive drum  7  is transferred onto the recording medium  2  by applying a predetermined voltage, the polarity of which is opposite to that of the toner image, to the image transferring roller  4 . Thereafter, the toner particles which are remaining on the photosensitive drum  7  are removed by the cleaning means  10 ; the toner particles remaining on the peripheral surface of the photosensitive drum  7  are scraped off and are collected into a waste toner bin  10   b  by an elastic cleaning blade  10   a  disposed in contact with the peripheral surface of the photosensitive drum  7 . 
     Referring to FIG. 3, as a lid  35  located at the top-right portion of the main assembly  14  is opened by being pivoted about a hinge  35   a,  unillustrated guide rails are exposed, which are located, one for one, on the left and right sides, and diagonally extend downward from the top-right toward the bottom-left. Next, referring to FIG. 6, the process cartridge B is provided with two circular guides, one of which is located at the longitudinal end on the left side, and the other of which is located at the longitudinal end on the right side. The center of the circular guide is in alignment with the rotational axis of the photosensitive drum  7 . This circular guide is fitted in a positioning groove located at the bottom end of the guide rail. Further, the process cartridge B is provided with two attitude controlling guides  13   n,  one of which is located at the longitudinal end on the left side, and the other of which is located at the longitudinal end on the right side. The guide  13   n  may be either integral with, or independent from, the circular guide, and fits with the aforementioned guide rail. When inserting the process cartridge B into the apparatus main assembly  14 , these circular guides and attitude controlling guides  13   n  are fitted with the correspondent guide rails. 
     The process cartridge B can be removed by a user from the main assembly  14 , by pulling the process cartridge B in the direction from the bottom-left to the top-right, that is, the direction opposite to the aforementioned inserting direction. 
     When inserting or removing the process cartridge B, the fingers of the user are to be placed on the surface of the indentation  17  of the top frame  11   a  and the bottom surface of the bottom frame  11   b.  The surfaces on which the fingers of the user are to be placed are provided with ridges  11   c.  The toner frame  11 , or the toner container portion, is constituted of the top frame  11   a  and the bottom frame  11   b,  which are welded at their interface U. 
     Frame Structure of Process Cartridge 
     The process cartridge B in this embodiment comprises an image developing unit D and a cleaning unit C, which are connected to each other by a connecting pin  22  in such a manner that they are allowed to pivot, relative to each other, about the connecting pin  22 . The image developing unit D comprises the toner frame  11  and an image development frame  12 , which are welded to each other at locations designated by referential codes  701   a  and  701   b.  The toner frame  11  constitutes a toner container (toner storage) which stores toner, and the image development frame  12  holds an image developing means  9 , such as the image developing roller  9   c.  The cleaning unit C is constituted of a cleaning unit frame  13 , and the functional components: the photosensitive drum  7 , the cleaning means  10  such as the cleaning blade  10   a,  and the charging roller  8 , which are mounted in the cleaning unit frame  13 . Next, referring to FIG. 2, the image development frame  12  and cleaning unit frame  13  are provided with a spring holder (now shown) and spring holder  13   b,  respectively, approximately in the form of a rod, and one end of a compressed compression spring  23  is fitted around the unshown spring holder and the other end of the spring  23  is fitted around the spring holder  13   b.  With this arrangement, the cleaning unit frame  13  and the image development frame  12  are kept under the pressure of the spring  23 , which presses the cleaning unit frame  13  and the image development frame  12  in the counterclockwise and clockwise direction, respectively, about a hole, or the connecting pin  22 , so that the peripheral surface of the photosensitive drum  7  is kept in contact with spacer rings  9   i  fitted around the longitudinal ends, one for one, of the image developing roller  9   c.    
     Method For Connecting Cleaning Unit Frame With Image Development Frame 
     The method for connecting the cleaning unit C and the image development unit D will be described with reference to FIGS. 1,  2 ,  6 , and  7 . FIG. 6 depicts the cleaning unit frame  13  and the connecting pin  22 . 
     Referring to FIGS. 2 and 7, each of the longitudinal ends of the image development frame  12  is provided with an arm  19 , which projects toward the cleaning unit frame  13 . At the end of the arm  19  of the development frame  12 , a hole  20  is provided, which is in alignment with the hole of the arm  19  on the other side of the development frame  12 . Each longitudinal end of the cleaning unit frame  13  is provided with a lateral plate  13   a,  which is on the outward side, and a lateral plate  13   f,  which is on the inward side. The gap between the two lateral plates  13   a  and  13   f  is slightly larger than the thickness of the arm  19 . They are provided with holes  13   eo  and  13   ei,  respectively, which are aligned in the longitudinal direction of the process cartridge B, that is, the direction parallel to the photosensitive drum  7 . The diameter of the hole  13   eo  is larger than that of the hole  13   ei.    
     The cleaning unit frame  13  and the image developing unit frame  12  are connected in the following manner. First, the arm  19  of the image developing unit frame  12  is inserted into the gap between the outer lateral plate  13   a  and the inner lateral plate  13   f  of the cleaning unit frame  13 , roughly aligning the holes  13   e  ( 13   ei  and  13   eo ) of the cleaning unit frame  13  and the hole  20  of the image developing unit frame  12  with the holes  20  of the image developing unit frame  12  roughly aligned with the holes  13   e  ( 13   ei  and  13   eo ) of the cleaning unit frame  13 . Then, the connecting pin  22  is inserted through the holes  13   e  and the hole  20  from the outside, at both longitudinal ends. The dimensional relation between the external diameter of the connecting pin  22  and the diameter of the hole  13   e  ( 13   eo  and  13   ei ) of the cleaning unit frame  13  is such that the connecting pin  22  fits in the holes  13   e  in the manner of an interference fit, whereas the dimensional relationship between the external diameter of the connecting pin  22  and the diameter of the hole  20  of the developing unit frame  12  is such that the connecting pin fits in the hole  20  in the manner of a clearance fit; in other words, the pin  22  fits in the hole  13   e  ( 13   eo  or  13   ei ) of the cleaning unit frame  13  tightly enough so that the pin  22  does not come out unless it is pulled with a force greater than a predetermined force. Therefore, after the two frames are connected by pressing the connecting pin  22  through the holes of the two frames, the cleaning unit frame  13  is pivotally supported by the connecting pin  22 . 
     FIG. 1 is a section of the joint between the cleaning unit frame  13  and the image developing unit frame  12 , depicting the connecting pin  22  and the area adjacent thereof. 
     The connecting pin  22  is a pin formed of steel, or nonferrous metallic material such as brass, by cutting, grinding, or cold forming. It is constituted of a small diameter portion  22   s,  which has a diameter d 1 , an intermediary portion  22   d,  which is tapered, and a large diameter portion  22   b,  which has a diameter d 2 . An arrow mark designated by a reference character a indicates the direction in which the connecting pin  22  is inserted; the drawing depicts the connecting pin  22  after the process cartridge B has been completely assembled. As is evident from the drawing, the connecting pin  22  is inserted inward into the holes from the outward side of the cleaning unit frame  13 . 
     In this embodiment, the diameter d 1  of the small diameter portion  22   s  of the connecting pin  22  is 3.0 mm (maximum tolerance: 0.0000 mm; minimum tolerance: −0.0015 mm); the diameter d 2  of the large diameter portion of the connector pin  22  is 3.5 mm (maximum tolerance: +0.2200 mm; minimum tolerance: +0.0040 mm, in JIS standard M8). The diameters of the holes  13   ei,    13   eo,  and  20   a  are 3.0 mm (maximum tolerance: −0.0400 mm; minimum tolerance: −0.0650 mm), 3.5 mm (maximum tolerance: −0.0300 mm; minimum tolerance: −0.0600 mm), and 3.0 mm (maximum tolerance: +0.0280 mm; minimum tolerance: +0.0140 mm, in JIS Standard E8), correspondingly. 
     Therefore, as the connecting pin  22  is put through the holes  13   eo,    20 , and  13   ei,  the small diameter portion  22   s  of the connecting pin  22  fits in the holes  13   ei  of the cleaning unit frame  13 , with the presence of interference, and also in the hole  20  of the image developing unit frame  12 , with the presence of clearance, whereas the large portion  2   d  of the connecting pin  22  fits in the hole  13   eo  of the cleaning unit frame  13 , with the presence of interference. Consequently, the image developing unit frame  12  becomes pivotable about the connecting pin  22 . As is evident from the above description, according to the frame connecting method in this embodiment, the connecting pin  22  is fitted into the two holes of the cleaning unit frame  13 , in the form of interference fitting, being rendered more resistant to the force which works on the connecting pin  22  in the direction to pull out the connecting pin  22 . 
     The measured force necessary to pull out the connecting pin  22  by applying pressure to the intermediary portion  22   d  was approximately 5 kg, which is large enough to render the connecting pin  22  resistant to the force that works on the connecting pin  22  in the direction to pull out the connecting pin  22  in the normal usage of the process cartridge B. 
     Referring to FIG. 1, the designs of the cleaning unit frame  13  and the connecting pin  22  are such that the outward end portion  22   c  of the fully inserted connecting pin  22  is slightly below, or even with, the outward surface  13   x  of the cleaning unit frame  13 . The objective of this arrangement is to prevent the user from accidentally pulling out the connecting pin  22 , that is, from accidentally separating the cleaning unit C from the image developing unit D. A structure that can more reliably prevent the connecting pin  22  from being pulled out is shown in FIG.  8 . In this case, the end portion  22   c  of the connecting pin  22  is covered with a cap portion  13   z  formed by melting a portion of the cleaning unit frame  13 , adjacent to the connecting pin  22 , so that the connecting pin  22  cannot be pulled out. In this embodiment, thermal welding is used to cover the end portion  22   c  by melting the portion of the cleaning unit frame  13 , but vibration welding, supersonic welding, gluing, or the like may be used to obtain the same result. Further, resin may be applied to the end portion  22   c  and the adjacencies thereof in the manner of cladding. 
     Embodiment 2 
     In Embodiment 2, the connecting pin  22  comprises three portions with different diameters: a small diameter portion  22   s;  a medium diameter portion  22   m,  the diameter of which is larger than that of the smaller diameter portion  22   s;  and a large diameter portion  22   b,  the diameter of which is larger than that of the medium diameter portion  22   m.  The small diameter portion  22   s  is pressed into the hole  13   ei  of the inward plate  13   f  of the cleaning unit frame  13 , and the large diameter portion  22   b  is pressed into the hole  13   eo  of the outward plate  13   a  of the cleaning unit frame  13 . The medium diameter portion  22   m  is fitted in the hole  20  of the arm  19  of the image developing unit frame  12 , in a freely rotatable manner. 
     This structural arrangement affords more latitude in selecting the diameters of the holes  13   ei,    20 , and  13   ei,  and the diameters of the portions  22   s,    22   m,  and  22   b  of the connecting pin  22 . 
     Embodiment 3 
     FIG. 10 depicts the third embodiment of the present invention. According to this embodiment, the cleaning unit frame  13  is provided with a bracket  13   g  with a hole  13   ee,  in addition to the outward plate  13   a  and inward plate  13   f.  The bracket  13   g  is on the inward side of the inward plate  13   f,  a predetermined distance apart from the inward plate  13   f.  The hole  13   ee  is slightly smaller in diameter than the hole  13   ei,  and is in alignment with the holes  13   eo  and  13   ei.    
     On the other hand, the connecting pin  22  comprises a larger diameter portion  22   b,  a small diameter portion  22   s,  which is immediately next to the large diameter portion  22   b,  and an anchor portion  22   t,  which is immediately next to the small diameter portion  22   s.  The large diameter portion  22   b  fits in the hole  13   eo  of the outward plate  13   a  of the cleaning unit frame  13 , in the manner of an interference fit, whereas the small diameter portion  22   s  of the connecting pin  22  fits in the hole  20  of the arm  19  of the image developing unit frame  12 , in the manner of a clearance fit. The anchor portion  22   t  of the connecting pin  22 , which is tapered toward the inward end, is pressed into the hole  13   ee  of the bracket  13   g.  Further, the small diameter portion  22   s  of the connecting pin  22  fits in the hole  13   ei  of the cleaning unit frame  13 , in the manner of an interference fit. 
     According to the third embodiment, the connecting pin  22  is more firmly held by the cleaning unit frame  13 , compared to the preceding embodiments. 
     As is evident from the above description of the preferred embodiments of the present invention, according to the present invention, the connecting pin that connects the first and second frames of a process cartridge is fixed to two or more locations on the first frame, providing a functional advantage in that the connecting pin is rendered more resistant to the force that works on the connecting pin in the direction to pull it out. Therefore, the connecting pin does not unexpectedly come out. 
     Further, the process cartridge structure in accordance with the present invention renders the molding of the first frame easier. Consequently, the dimensional accuracy of the first frame is improved. Further, in terms of the economic aspect of the process cartridge B, the cost of the process cartridge B can be reduced, since the process cartridge structure in accordance with the present invention makes it easier to produce the metallic mold for the process cartridge. 
     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.