Patent Publication Number: US-4839690-A

Title: Image bearing member usable with image forming apparatus

Description:
This application is a continuation of application Ser. No. 906,032 filed Sept. 10, 1986, now abandoned. 
    
    
     FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image bearing member such as a photosensitive drum and an insulating drum, usable with an electrophotographic copying machine or electrostatic recording machine, more particularly, a mechanism for electrically connecting the image bearing member with an associated main assembly of the apparatus, wherein on the surface of the image bearing member a latent image or toner image is formed. 
     In one method of producing a small size image bearing drum, an impact formation is used wherein one longitudinal end of the drum is closed during the formation, so that it is formed into a shape of a cup. When such a shape of the drum is used as a photosensitive drum, a part of the end can be formed into a shaft, which is utilized for electrically connecting the photosensitive drum to an external machine. 
     However, when the size, more particularly diameter of the drum is reduced, which is a recent trend, it is not possible to close one longitudinal end in the impact formation. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a principal object of the present invention to provide an image bearing member which can be electrically connected to an external assembly in the case where the diameter of the drum is reduced. 
     It would be easy to establish the electrical connection by employing a metal flange at the end of the drum. However, this results in the increase of the weight and the manufacturing cost. 
     Therefore, it is another object of the present invention to provide an image bearing drum which does not use a flange of a metal. 
     It is a further object of the present invention to provide a mechanism for establishing electrical connection, which has a minimum length measured in the direction perpendicular to the direction of movement of the image bearing member. 
     According to an embodiment of the present invention, there is provided an image bearing member usable with an image forming apparatus, comprising an electrically conductive drum member supporting thereon an image bearing layer; an electrically insulative flange mounted adjacent an end of said conductive drum member; and an electrically conductive member, engageable with an electrically conductive member of the image forming apparatus, disposed at an inner side of said flange and engaged to a part of the conductive drum. 
     The image bearing member may in the form of a drum or cylinder comprising a conductive base and an image bearing member or in the form of an insulating drum comprising an insulating or dielectric layer, or may be a combination of such an image bearing member in the form of a belt and a roller or drum for supporting such a belt. 
     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 partly broken perspective view of an image bearing member (a photosensitive drum) according to an embodiment of the present invention. 
     FIG. 2 is a sectional view illustrating the relationship between the photosensitive drum of FIG. 1 and a main assembly in which the photosensitive drum is mounted. 
     FIG. 3 is a partly broken perspective view illustrating the conductive plate. 
     FIG. 4 is a perspective view of another example of a flange. 
     FIGS. 5 and 6 are sectional views illustrating the establishment of electrical connection. 
     FIG. 7 is a perspective view of another example of the image bearing member, in the form of a combination of a belt and a roller. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown a part of a photosensitive drum employing an electrical contact establishing mechanism according to an embodiment of the present invention, in a partly broken perspective view. FIG. 2 illustrates the connection with the main assembly to which the photosensitive drum is set. In this embodiment, the photosensitive drum is built in a process cartridge as disclosed in U.S. Pat. No. 4,575,221. 
     The photosensitive drum 1 is in the form of a drum or cylinder having both ends opened. It is made of aluminum and has a diameter of 30 mm. To each of the ends, a resin flange 2 or 3 of polyacetal resin or polycarbonate resin is mounted. One of the resin flanges 2 is provided with an engaging portion 2a at which the flange is journaled in the cartridge housing 4, whereby the drum 1 is supported in the cartridge housing 4. The resin flange 2 is also provided with a bore 2b which is effective to receive a positioning pin 6 of the main assembly, which pin 6 is mounted to and electrically connected with a side plate 5 of the main assembly. By the receiving engagement, the cartridge is supported to the main assembly. The other flange 4 supports the photosensitive drum 1 on the cartridge housing 4 through another positioning pin 7. 
     The photosensitive drum 1 is driven by a gear of the main assembly by an engagement with the gear of the main assembly and the gear portion 2c integrally formed with the flange 2. 
     A conductive plate 8 serves to electrically connect the drum 1 with an external portion, more particularly, to ground the drum 1 in this embodiment. The conductive plate is made of steel, copper phosphor bronze or stainless steel in the form of a thin plate. The conductive plate 8 is securedly fitted to an internal wall of the photosensitive drum 1 so that the electrical connection is established with the drum, and simultaneously, the position of the conductive plate 8 is fixed. The conductive plate is stamped to form a leaf spring portion 8b. When the cartridge is mounted in the main assembly, the leaf spring 8b is contacted to a free end of the positioning pin 6 of the main assembly, whereby the electrical connection is established between the metal portion of the photosensitive drum 1 and the main assembly. 
     The conductive plate 8 is properly mounted by fixing it to the flange 2, before the resin flange 2 is mounted into the drum, by a screw or screws 9 or by clamping the conductive plate 8 by deforming the resin part by heat. By doing so, the positioning and fixing of the conductive plate 8 is assured. 
     FIG. 4 shows another example of driving mechanism of the drum 1, wherein the gear portion 2c of the flange 2 of FIG. 1 example is not used. In the example of FIG. 4, a transmission element 10 is fixed on the pin 6. The transmission element 10 has a projection or projections 10a which is engageable with a recess or recesses 2d formed in the resin flange 2, so that the drum 1 is driven by the positioning pin 6 which rotates. This will be further described. 
     Referring to FIGS. 5 and 6, the main assembly of the image forming apparatus, which is an electrophotographic machine in this embodiment, comprises a driving shaft 6 which functions to transmit a driving force to the process cartridge and also to position the drum 1 of the processcartridge. A transmission element 10 is mounted on the driving shaft 6 by parallel pins 11, wherein the transmission element 10 is not rotatable relative to the driving shaft 6 but is slidable thereon. The transmission element 10 has two projections 10a. The transmission element 10 is urged toward the drum by a spring 12. The driving shaft 6 is supported by a bearing 13 which is mounted to a fixed side plate 14 of the main assembly. The driving shaft 6 is driven by a driving source of the main assembly through a driving gear 15. The driving gear 15 is mounted on the driving shaft 6, wherein the gear 15 is not rotatable relative to the driving shaft 6, but is slidable thereon. The driving shaft 6 is further supported by a bearing 17 which is mounted to a fixed side plate 18 of the main assembly. The photosensitive drum 1 of the process cartridge has a resin flange 2 which is pressure-fitted into the photosensitive drum 1. A conductive plate 8 is effective to apply a bias voltage to the photosensitive drum from the main assembly by way of the driving shaft 6 in the manner described above. The bias voltage may be the ground level. The conductive plate 8 is fixed to the resin flange and is also engaged to the internal surface of the photosensitive drum 1. 
     As will be understood from the Figures, the drum gear 2c is located at such a position that it does not extend out of the cartridge housing 4. The drum gear 2c is used to transmit the driving force to another means in the process cartridge, such as a developing device or a cleaning device (not shown). 
     When the process cartridge is mounted into the copying apparatus, the driving shaft 6 of the main assembly is inserted into the central bore 2b of the resin flange so that the drum 1 is correctly positioned with respect to the main assembly, and so that the free end of the driving shaft 6 pushes the leaf spring 8b of the conductive plate 8 and is pressure-contacted thereto. The two projections 10a of the transmission element 10 is pushed into the recesses 2a at the inside part of the resin flange 2 by the spring 12. When the driving source of the main assembly operates, the driving force is transmitted to the gear 15 to rotate the drive transmission element 10 which is engaged to the driving shaft 6 by the parallel pins 11. The projections 10a of the transmission element 10 rotates the resin flange 2, and therefore, the photosensitive drum 1 which is fixed to the flange 2. During the rotation of the photosensitive drum 1, the flange 2 rotationally slides in the process cartridge housing 4 at the bearing portions. 
     FIG. 6 illustrates the state in which the process cartridge is being mounted into the copying apparatus. FIG. 5 illustrates the state in which it has been set in place therein. 
     As will be understood from the Figures, in this embodiment, the conductive plate 8 mounted to the resin flange is at such a position which is away from the external surface of the wall of the cartridge housing 4 by a distance 1. The image bearing member 1 has a region L in which an image can be formed or carried. When the cartridge is mounted in the main assembly, the driving shaft 6 of the main assembly extends into the image forming region L. In other words, the conductive plate 8 and its leaf spring 8b is within the image forming region L of the image bearing member. By this arrangement, the total length of the photosensitive drum 1 including the necessary elements, is reduced as compared with conventional arrangements. As a result, the size of the process cartridge can be reduced. 
     In the foregoing embodiment, the insulating flange 2 is made of a resin. However, it is possible to use processed paper, ceramic, processed wood or the like. 
     The electric connection may be to ground the image bearing member or to apply a positive or negative voltage thereto. 
     As for the image bearing drum, it may be built in the process cartridge or may be a drum itself. The image bearing member may be an insulating drum having a surface layer capable of retaining electric charge. 
     In the embodiment described above, the photosensitive drum 1 is an electrophotographic photosensitive member, around which charging means, image exposure means, developing means, image transfer means and cleaning means are disposed in the order named, which may be of any known type. The detailed description of those means is omitted for the sake of simplicity. 
     The image bearing member may be of a type wherein an insulating layer or dielectric layer is formed on a conductive base. The shape thereof is not limited to the drum or cylinder, but may be a belt. 
     FIG. 7 is an example of the image bearing member 1 in the form of a combination of a belt and a roller. An electrophotographic photosensitive belt 19 comprises an electrically conductive base belt 21 of a metal and a photoconductive surface layer 20 thereon. The photosensitive belt 19 is supported around the supporting drums 22, 23 and 24 of a conductive material such as aluminum and stainless steel. At least one of those drums may have the same structure as shown in FIG. 2 or 5, in which case the drum functions as a driving drum, and the other drums function as follower drums. By doing so, the photosensitive belt 19 is capable of being driven. In this case, the driving drum corresponds to the photosensitive drum 1 of the foregoing embodiment, the electrical connection is established by the conductive plate 8 of FIG. 2 or 5 through the driving drum with the main assembly. 
     In this case, similarly to the case of the image bearing member in the form of a drum, the conductive plate 8 is disposed within the width of the belt in the direction perpendicular to the movement of the belt. Thus, both of the flange 2 and the conductive plate 2 is disposed within the image forming region of the image bearing member, so that the width or length of the image bearing member is minimized, allowing efficient use of the space. 
     As will be understood, according to the present invention, the flange portion can be formed by a separate member from the drum, and therefore, the latitude of selection of the shape and material of the flange is increased. Also, since the flange may be of an insulating material, the weight and the manufacturing cost of the flange is reduced as compared with a metal flange. Further, the conductive member for establishing the necessary electrical connection is disposed inside the conductive drum member, and therefore, the position of the conductive member is relatively free to such an extent that the conductive member may be located within the image forming range of the image bearing member. More particularly, it is not necessary to establish an electrical contact at the surface of the image bearing member, which is effective to minimize the width of the image bearing member. 
     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.