Abstract:
A ground plate for a photosensitive drum assembly including a planar member having a central portion and a plurality of legs extending from the central portion. Each of the legs includes at least one projection extending therefrom. The projections are configured to scratch the inner surface of a photosensitive drum to make electrical contact between the ground plate and the photosensitive drum. The ground plate also includes a central aperture including spring contacts for engagement with a ground pin.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention to relates to the field of ground plates, and more particularly to a ground plate for a photosensitive drum and improvements thereto.  
           [0003]    2. Description of the Related Art  
           [0004]    Photosensitive drums for use in image forming devices such as copying machines, facsimile machines, and printers are well known in the art. A typical photosensitive drum includes a hollow metal cylinder having an organic or non-organic photoconductive layer on the outer surface and a pair of end caps, as disclosed, for example, by U.S. Pat. No. 5,729,792 to IKEHARA et al., U.S. Pat. No. 6,006,053 to IKEHARA, and U.S. Pat. No. 5,943,527 to KASHIWAGI et al. The typical photosensitive drum assembly also includes a nonconductive flange inserted in each end of the photosensitive drum, a support axle passing through the drum via apertures in the flanges, and a ground plate attached to the inner surface of one or both of the flanges.  
           [0005]    The prior art also includes a photosensitive drum cartridge, as disclosed, for example, by U.S. Pat. No. 4,839,690 to ONODA et al. This drum cartridge includes a hollow metal cylinder having a photosensitive layer, a pair of resin flanges inserted in the ends of the cylinder and a pair of positioning pins or drum shafts for supporting the drum cartridge, and a conductive plate attached to the inner surface of one of the flanges. A leaf spring portion of the conductive plate contacts the end face of one of the positioning pins.  
           [0006]    A disadvantage of the prior art is the complicated nature of the ground plates. The prior art ground plates have particularly intricate and complicated shapes that are difficult to manufacture. Additionally, the manufacture of some of the prior art ground plates also includes several steps after cutting or stamping since the contact members for the ground pin must be folded back toward the center of the ground plate following the cutting or stamping of the ground plate.  
           [0007]    Another disadvantage of the prior art is the disc shape of the prior art ground plates. The disc shaped ground plate consumes unnecessary material. Acceptable electrical contact to provide high quality grounding does not require that the entire end cap be covered. Therefore, it is not necessary to form the ground plate in a disc shape and waste valuable material. Another disadvantage of the disc shape of the prior art ground plate is that it is dangerous to handle. The disc shaped ground plate of the prior art includes projections about the entire circumference of the ground plate. The projections are very sharp in order to scratch the inner surface of the photosensitive drum. Therefore, sharp projections extend from the entire edge of the ground plate, and it is extremely difficult to quickly find a safe spot to grasp when handling the ground plate. Many handlers of such ground plates have been injured.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed to a ground plate for a photosensitive drum in an image forming device, which addresses the problems existing in the prior art, discussed above.  
           [0009]    An aspect of the present invention provides a ground plate for a photosensitive drum assembly, including a substantially planar member, the substantially planar member including a central portion, and a plurality of legs extending from the central portion, at least one projection extending from each of the plurality of legs, each of the projections being configured to scratch an inner surface of a photosensitive drum in the photosensitive drum assembly to make electrical contact between the ground plate and the photosensitive drum. The legs may extend in directions substantially parallel to each other. Further, each of the projections may extend in directions substantially parallel to each other.  
           [0010]    According to a further aspect of the present invention, the plurality of legs may include four legs, and the central portion and the four legs may substantially form an H shape. Further, each of the legs may include two projections extending therefrom to scratch the inner surface of the photosensitive drum, and the projections may extend out of the plane of the substantially planar member.  
           [0011]    In a further aspect of the present invention, the substantially planar member may include a two piece construction. The substantially planar member may further include a first leg and a second leg, each of the first leg and the second leg including a spring contact extending from a central portion thereof, the first and second legs being spaced from each other to secure a ground pin therebetween when fixed to an end cap. The ground plate may farther include a central aperture in the central portion, and a plurality of spring contacts extending into the central aperture, wherein the central aperture receives a ground pin therethrough and the plurality of spring contacts engage the ground pin to make electrical contact between the ground plate and the ground pin. Further, the ground plate may include two spring contacts. The ground plate may further include a plurality of apertures provided in the substantially planar member, each of the apertures being configured to receive a protrusion on an end cap of the photosensitive drum assembly, and a plurality of projections provided in each of the apertures, the projections being configured to engage the protrusions on the end cap of the photosensitive drum received in the apertures and to fix the ground plate to the end cap of the photosensitive drum.  
           [0012]    A further aspect of the present invention provides a photosensitive drum assembly for an image forming device including a photosensitive drum, the drum including a photosensitive layer on an outer surface thereof, a first end cap and a second end cap, the end caps being configured to fit into the ends of the drum, and a ground plate fixed to an inner face of the first end cap, the ground plate including a substantially planar member, the substantially planar member including a central portion, and a plurality of legs extending from the central portion, at least one projection extending from each of the plurality of legs, each of the projections being configured to scratch an inner surface of the photosensitive drum to make electrical contact between the ground plate and the photosensitive drum. The photosensitive drum assembly may further include a ground pin extending through an aperture in the first end cap, and the ground plate further including a central aperture in the central portion, and a plurality of spring contacts extending into the central aperture, wherein the central aperture receives the ground pin therethrough and the plurality of spring contacts engage the ground pin to make electrical contact between the ground plate and the ground pin.  
           [0013]    Another aspect of the present invention provides an image forming device including a printer engine, and a photosensitive drum assembly mounted in the printer engine, the photosensitive drum assembly including a photosensitive drum including a photosensitive layer on an outer surface thereof, a first end cap and a second end cap, the end caps being configured to fit into the ends of the drum, and a ground plate fixed to, an inner face of the first end cap, the ground plate including a substantially planar member, the substantially planar member including a central portion, and a plurality of legs extending from the central portion, at least one projection extending from each of the plurality of legs, each of the projections being configured to scratch an inner surface of the photosensitive drum to make electrical contact between the ground plate and the photosensitive drum. The image forming device may further include an engine frame, a spring ground contact mounted on the engine frame, the photosensitive drum assembly further including a ground pin extending through an aperture in the first end cap, the ground plate further including a central aperture in the central portion, and a plurality of spring contacts extending into the central aperture, wherein the central aperture receives the ground pin therethrough and the plurality of spring contacts engage the ground pin to make electrical contact between the ground plate and the ground pin, and wherein the ground pin is configured to contact the spring ground contact to make electrical contact between the ground pin and the spring ground contact to ground the photosensitive drum. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The above and other objects, features and advantages of the present invention will be made apparent from the following description of the preferred embodiments, given as nonlimiting examples, with reference to the accompanying drawings in which:  
         [0015]    [0015]FIG. 1 is an exploded side view of a printer including an organic photoconductor (OPC) drum and which may include the present invention;  
         [0016]    [0016]FIG. 2 is an exploded perspective view of an OPC drum and which may include the present invention;  
         [0017]    [0017]FIG. 3 is a front view of a ground plate according to a first embodiment of the present invention;  
         [0018]    [0018]FIG. 4 is a perspective view of the ground plate of FIG. 3;  
         [0019]    [0019]FIG. 5 is a side view of the ground plate of FIG. 3;  
         [0020]    [0020]FIG. 6 is a sectional view of the drum shown in FIG. 2 and including the ground plate of FIG. 3 in position in the drum;  
         [0021]    [0021]FIG. 7 is a front view of a second embodiment of the ground plate of the present invention; and  
         [0022]    [0022]FIG. 8 is a front view of a third embodiment of the ground plate of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description is taken with the drawings making apparent to those skilled in the art how the forms of the present invention may be embodied in practice.  
         [0024]    With reference to FIGS.  1 - 6  of the drawings, reference numeral  1  denotes an image forming apparatus such as, for example, a printer, copying machine, or facsimile machine of the present invention. The image forming apparatus includes a photosensitive drum assembly  2  on which is formed an electrostatic latent image. A developing device provides oppositely charged toner to adhere to the photosensitive drum and form an image. This image is then transferred to a substrate, such as paper.  
         [0025]    The photosensitive drum assembly  2  includes a photosensitive drum  3 . The photosensitive drum  3  may be any type known to those of skill in the art, and in the present invention, includes an organic photoconductor (OPC) drum. The photosensitive drum  3  is a hollow cylinder constructed of an electrically conductive material such as, for example, aluminum. The photosensitive drum  3  is coated on the outer surface with a layer of photoconductive material  4  and includes an anodized inner surface. The photosensitive drum assembly  2  includes a front end cap  6  and a rear end cap  7 . The front end cap  6  and rear end cap  7  are constructed of an insulative material such as for example, plastic or resin. The front end cap  6  and rear end cap  7  each have an appropriate diameter so as to engage in a press fit with the ends of the photosensitive drum  3 .  
         [0026]    As shown in FIG. 2, the front end cap  6  includes an inner face  8 , an outer face, a center aperture  10 , and a plurality of protrusions  11  extending from the inner face  8 . The front end cap  6  may include any suitable number of protrusions  11 , and in the present embodiment includes four protrusions  11 . The photosensitive drum assembly  2  further includes a ground plate  12 . The ground plate  12  is substantially planar and is constructed of any suitable electrically conductive material such as, for example, metal, including spring steel, and may be formed by any suitable process such as, for example, stamping. The ground plate  12  includes a plurality of apertures  13 , preferably corresponding in number to the number of protrusions  11  extending from the inner face  8  of the front end cap  6 . Each of the apertures  13  in the ground plate  12  include a plurality of projections or tabs  14  extending toward the center of the aperture  13 . Each aperture  13  may include any suitable number of tabs  14 , and in the present embodiment, includes four tabs  14 . The circumference of each of the apertures  13  is larger than the circumference of each of the protrusions  11 . The front end cap  6  and the ground plate  12  are assembled by inserting the protrusions  11  extending from the inner face  8  of the front end cap  6  into the apertures  13  in the ground plate  12 . The tabs  14  extend into the apertures  13  a sufficient distance such that the ground plate  12  is frictionally fixed to the inner face  8  of the front end cap  6  by engagement between the tabs  14  and the edges of the protrusions  11 . The tabs  14  are pliable and may be bent or folded due to the assembly of the ground plate  12  and the front end cap  6 . Alternatively, the tabs  14  may be pre-bent so as to aid in the assembly.  
         [0027]    The ground plate  12  has substantially an H shape including four legs  15  connected by central portion or cross member  16 . Each of the legs  15  includes a plurality of pointed projections  17  extending therefrom. Each leg  15  may include any suitable number of projections  17 , and in the present embodiment includes two projections  17 . The projections  17  may extend from the plane of the ground plate  12 , or alternatively, the projections  17  may be pre-bent. The ground plate  12  further includes a central aperture  18 . Extending into the aperture  18  are a plurality of arms or spring contacts  19 . The ground plate may include any suitable number of spring contacts  19 , and in the present embodiment includes two spring contacts  19 . Each spring contact  19  may be pre-bent from the plane of the ground plate  12 , and each spring contact  19  may include a pre-bent end portion  20 .  
         [0028]    The assembly of the front end cap  6  with the ground plate  6  frictionally affixed thereto is inserted into an end of the photosensitive drum  3 . The front end cap  6  has an appropriate circumference so as to engage in a frictional fit with the inner surface of the photosensitive drum  3 . The projections  17 , either planar or pre-bent, extend from the ground plate  12  a sufficient distance so that when the ground plate and front end cap assembly is inserted into the photosensitive drum  3 , the projections  17  contact the inner surface of the photosensitive drum  3 . The projections  17  scrape or scratch the anodized inner surface of the photosensitive drum  3 , making electrical contact between the ground plate  12  and the photosensitive drum  3 . By scratching through the anodized surface of the photosensitive drum  3 , the ground plate  12  provides improved electrical contact with the aluminum core of the photosensitive drum  3  which is necessary for proper printer operation. This contact must then be carried to the printer engine frame such that the photosensitive drum  3  is electrically grounded to the engine frame  21 .  
         [0029]    As shown in FIG. 6, the photosensitive drum assembly  2  further includes a ground pin  22  having a flat portion  23 . The ground pin  22  is inserted through the center aperture  10  of the front end cap  6  and the central aperture  18  of the ground plate  12 . The flat portion  23  of the ground pin  22  engages with a flat portion  23   a  in the center aperture  10  of the front end cap  6 , preventing rotation between the ground pin  22  and the front end cap  6 . The ground pin  22  extends through the central aperture  18  of the ground plate  12  so that the end portions  20  of the spring contacts  19  contact the side of the ground pin  22 . The ground plate  12  may be constructed of a flexible material that is springy, such as spring steel, so that the end portions  20  of the spring contacts  19  tightly and securely contact the ground pin  22 , making good electrical contact between the ground plate  12  and the ground pin  22 . The ground pin  22  will be electrically connected to the printer engine frame  21  when the photosensitive drum assembly  2  is installed in the printer.  
         [0030]    The photosensitive drum assembly  2  further includes a front support bearing  24  and a rear support bearing (not shown). The front support bearing  24  is slid onto the front end cap  6 ; and the rear support bearing is slid onto the rear end cap  7 . The front support bearing  24  and rear support bearing provide support to the photosensitive drum assembly  2  in the image forming device  1 . The photosensitive drum assembly  2  rotates on the front and rear support bearings.  
         [0031]    The image forming device  1  further includes a front bearing support and a rear bearing support  25 , and a front bearing clamp and a rear bearing clamp  26 . It is noted that in FIG. 1 for simplicity of illustration, only the rear bearing support  25  and the rear bearing clamp  26  are shown. The photosensitive drum assembly  2  is installed into the image forming apparatus  1  by placing the photosensitive drum assembly  2  so that the front support bearing and rear support bearing are received by the front bearing support and the rear bearing support, respectively. The front bearing clamp and the rear bearing clamp are closed and secured around the front support bearing and the rear support bearing, respectively. The front and rear bearing clamps may include any suitable type of securing mechanism, and in the present embodiment, the front and rear bearing clamps are swung down over the bearings and fixed to the front and rear bearing supports, respectively, by screws. In this manner, the front and rear support bearings are fully encircled by the front and rear bearing supports and the clamps. The front support bearing and the rear support bearing are fully insulated by the front end cap and the rear end cap, and do not provide any grounding function for the photosensitive drum  2 . The front support bearing and the rear support bearing provide a support, positioning, and rotating mechanism for locating the photosensitive drum  2  in the printer engine frame  21 .  
         [0032]    The image forming apparatus  1  further includes a spring ground contact  27  mounted on the frame  21 , and a ground wire  28  connected to the engine frame  21 . The spring ground contact  27  is mounted on the frame  21  adjacent to an aperture  29  in the frame. When the photosensitive drum assembly  2  is installed in the image forming apparatus  1  and secured by the front and rear bearing supports and clamps, the ground pin  22  extending from the front end cap  6  contacts the spring ground contact  27 . The spring ground contact  27  tightly contacts the end of the ground pin  22 , making a good electrical connection. The ground wire  28  is connected to both the spring ground contact  27  and to the engine frame  21 . The ground wire  28  may be connected to the engine frame via associated wires and electrical connectors, making a reliable electrical connection. Through the ground plate  12 , the ground pin  22 , the spring ground contact  27 , the ground wire  28 , and associated wires and connectors, the photosensitive drum  3  is grounded to the frame  21 .  
         [0033]    With reference to FIG. 7 of the drawings, reference numeral  30  denotes a second embodiment of the ground plate. As in the first embodiment, the second embodiment of the ground plate  30  includes a plurality of apertures  31  with a plurality of tabs  32  extending toward the center of each aperture  31 , a plurality of legs  33 , a central portion  34 , and a plurality of projections  35  extending from each leg  33 . However, the second embodiment of the ground plate  30  includes a substantially rectangular central aperture  36  having a plurality of spring contacts  37  extending toward the center of the central aperture  36 . In the second embodiment of the ground plate  30 , the central aperture  36  and spring contacts  37  are formed without removing any material from the central portion  34  by stamping or cutting an H-shape in the central portion  34  of the ground plate  30 . The stamped or cut material may be folded back to form the spring contacts  37 .  
         [0034]    With reference to FIG. 8, reference numeral  38  denotes a third embodiment of the ground plate of the present invention. As in the first embodiment, the third embodiment of the ground plate  38  includes a plurality of apertures  39  with a plurality of tabs  40  extending toward the center of each aperture  39 . However, the third embodiment of the ground plate  38  includes a two piece construction including a first leg  41  and a second leg  42 , and a plurality of projections  43  extending from the first leg  41  and the second leg  42 . Further, in the third embodiment of the ground plate  38 , each leg includes a spring contact  44  extending from a central portion thereof, so that when the ground plate  38  is fixed to an end cap, a space between the spring contacts defines an aperture and receives a ground pin.  
         [0035]    Although the invention has been described with reference to an exemplary embodiment, it is understood that the words that have been used are words of description and illustration, rather than words of limitation. Changes may be made within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the invention in its aspects. Although the invention has been described with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed. Rather, the invention extends to all functionally equivalent structures, methods, and uses such as are within the scope of the appended claims.