Abstract:
If an edge of a sheet metal of an image forming apparatus damages an electric cable, the image signal is distorted and a correct image is not formed since the damage causes feeding failure and signal deterioration. This is remarkable in the conventional digital electrophotographic apparatus, since the drive signal to drive a laser or a light emitting diode (LED) for exposing the photosensitive body becomes higher in frequency as resolution and speed are increased and tends to generate the electric noise. In order to prevent damage of an electric cable by a metal frame, an apparatus having a holder for holding a feed cable is provided.

Description:
This application is a divisional of U.S. patent application Ser. No. 09/866,664, filed on May 30, 2001, now pending. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus such as a copying machine, facsimile apparatus and the like. 
   2. Related Background Art 
   In general, an image forming apparatus of an electrophotographic system forms an electrostatic latent image by exposing a charged photosensitive body to an image light, and after this electrostatic latent image is developed, it is transferred on a recording medium such as a paper or the like. 
   In such an image forming apparatus, an electric cable is used for feeding and transmitting a signal, and the cable is usually fixed to a sheet metal frame of the apparatus body. 
   As miniaturization of the apparatus has been progressing, restriction has come to be imposed on a wiring position and fixing position of the cable and sometimes the cable may come into contact with an edge of the metal frame. 
   In this case, since the edge of the sheet metal frame is sharp, the electric cable may be damaged, thereby causing feeding failure and signal deterioration. 
   Hence, a resin block is attached to the frame and the cable is fixed to this resin block, so that the cable can be prevented from contacting the edge. 
   However, since the resin block has an electric non-conductance, there arose a problem that an electric noise is generated when the cable transmits a high frequency. 
   Particularly, in a digital electrophotographic apparatus, the drive signal to drive a laser or a light emitting diode (LED) for exposing the photosensitive body becomes higher in frequency as a resolution and speed are increased and tends to generate the electric noise. 
   When this noise is superposed on an image signal, the image signal is distorted and a correct image is not formed. 
   SUMMARY OF THE INVENTION 
   The present invention can provide an image forming apparatus which prevents the damage of an electric cable by a metal frame. 
   The present invention can also provide an image forming apparatus in which the electric cable can be installed. 
   The present invention can further provide an image forming apparatus as described in the claims. 
   Yet further objects of the present invention will be apparent from the following description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a schematic configuration of an image forming apparatus according to an embodiment of the present invention; 
       FIG. 2  is a view showing a wiring of a feed cable provided for the image forming apparatus; 
       FIG. 3  is a schematic view of a holder of the embodiment of the present invention; 
       FIGS. 4A ,  4 B and  4 C are explanatory views explaining the configuration of the holder of the embodiment of the present invention; 
       FIG. 5  is an explanatory view explaining the wiring of the conventional feed cable; 
       FIGS. 6A and 6B  are explanatory views explaining a method of holding the feed cable; and 
       FIG. 7  is a prototype of an electric non-conductance resin holder built by the present inventor. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will be described in detail below with reference to the drawings. 
   First, an embodiment of the present invention will be described. 
   In the first place, an image forming process in the image forming apparatus adapting the electrophotographic system which is one example of the image forming apparatus according to the present embodiment will be explained with reference to  FIG. 1 . 
   In such an image forming apparatus, as shown in  FIG. 1 , first, second, third and fourth image forming sections Pa, Pb, Pc and Pd, which form images of respective colors of yellow, magenta, cyan and black, are installed. The image forming sections Pa, Pb, Pc and Pd comprise photosensitive drums  17   a  to  17   d  which are image bearing bodies, respectively, and on which, after being evenly charged by charging means  18   a  to  18   d , electrostatic latent images are formed by electrostatic latent image forming means  19   a  to  19   d,  which use the light emitting diode as an exposure light source. After that, the electrostatic latent images are developed by the toners of various colors by developing means  20   a  to  20   d , and the toner images are electrostatically transferred on a recording medium by transfer means  21   a  to  21   d  and then the toner images are fixed on the recording medium by heat and pressure of fixing means  12 . 
   Under the above described first, second, third and fourth image forming sections Pa, Pb, Pc and Pd from a cassette  11  which stores recording papers as the recording medium to the fixing apparatus  12 , a recording paper conveying belt as recording paper conveying means (hereinafter simply referred to as conveying belt)  13  in the shape of an endless belt which circularly moves through these image forming sections to convey the recording papers is installed. 
   The conveying belt  13  is a belt endlessly driven in the direction indicated by an arrow A by a drive roller  14  and bears the recording papers which are supplied from the cassette  11  and synchronized by a pair of registration rollers  15  and fed and conveyed in order to the above described image forming sections Pa, Pb, Pc and Pd. 
   The fixing apparatus  12  receives the recording paper discharged from the drive roller  14  side and collectively fixes the toner images of each color, which are superposed and transferred on the recording paper in the image forming sections Pa, Pb, Pc and Pd, on the above described recording paper and forms a permanent image, and thereafter discharges the above described recording paper to a discharge tray  16 . 
   A control line for electrically controlling the photosensitive drums  17   a  to  17   d  and the electrostatic latent image forming means  19   a  to  19   d  and the like of the above-described image forming sections Pa, Pb, Pc and Pd and a feed cable  24 , which is a power source line for supplying electric power to the image forming sections Pa, Pb, Pc and Pd finally reach, as shown in  FIG. 2 , the power source (not shown) and a control substrate  22  through the metal frame. The power source and control substrate  22  are usually installed at the rear of the apparatus. In the vicinity of the image forming sections, driving sources  23   a  and  23   b  are installed, respectively. In the case where these driving sources  23   a  and  23   b  avoid the metal frame  21  and try to secure a passage for the feed cable  24 , a wiring passage inevitably becomes long. Particularly in the case of the present embodiment such as the image forming apparatus comprising four image forming sections, the installation of the feed cable  24  is complicated. In order to make the wiring passage of the feed cable  24  the shortest, it is desirable to take out the feed cable  24  from the position close to the rear of the metal frame  21  in the image forming sections. 
   However, if the feed cable  24  is attached to the metal frame  21  as it is, the edge of the metal frame  21  inflicts damage to the feed cable  24 . 
   Therefore, the present inventor attached a holder  205  ( FIG. 7 ) made of electric non-conductance resin to the metal frame  201 , which protects and holds the feed cable  204 . Nevertheless, since the feed cable  204  has been transmitting high frequency electric signals, electric noises were produced, which were superposed on the high frequency electric signals, thereby disturbing the images. 
   In view of the above, the present inventor has attached, as shown in  FIG. 3 , a holder  30  comprising a substrate  25  made of resin and an electro-conductive sheet  28  to the metal frame  21 . 
   The electro-conductive sheet  28 , as shown in  FIG. 3  and  FIG. 4A , is installed in such a manner so as to go around from the side of the holder  30  to which the feed cable  24  is held to the side of the holder  30  that the metal frame  21  is contacted through a feed cable pressing member  29 . In this manner, the feed cable  24  held by the holder  30  can be electrically connected to the metal frame  21 . 
   When constituted in such a manner, the feed cable  24  is not brought into contact with the metal frame  21  and therefore is not damaged by the edge of the metal frame  21 . Further, since the feed cable  24  is grounded to the metal frame  21  through the electro-conductive sheet  28 , electric noise is removed and has no influence on the images. Furthermore, being made of resin, the substrate can be obtained in a desired shape and is inexpensive, compared to being made of metal. 
   Here, a method of holding the feed cable  24  in the image forming apparatus according to the present embodiment will be described. 
   Between a gap d 2  of the feed cable pressing member  29  of the holder  30  and a line diameter d 1  of the feed cable  24 , there exists a relationship of d 2 &lt;d 1  as shown in  FIG. 4B  and therefore, in a state in which the feed cable  24  is fitted with the pressing member  29 , the feed cable  24  is pressed against the electro-conductive sheet  28 . As a result, an earth can be securely taken between the feed cable  24  and the metal frame  21  through the electro-conductive sheet  28 . 
   The electro-conductive sheet  28  is, as shown in  FIG. 4C , divided into plural layers. 
   As an example of the layers constituting the electro-conductive sheet  28 , a first combination can be enumerated as follows: 
   A first layer . . . a surface electro-conductive layer, 
   A second layer . . . an adhesive layer. 
   Or a second combination as follows: 
   A first layer . . . a surface electro-conductive layer, 
   A second layer . . . a resin layer. 
   Or a third combination as follows: 
   A first layer . . . a surface electro-conductive layer, 
   A second layer . . . a resin layer, 
   A third layer . . . an adhesive layer. 
   Having the adhesive layer is much easier in attaching the electro-conductive sheet  28  to the substrate  25  of the holder  30  and excellent in working performance. Having the resin layer reinforces the electro-conductive layer  28  and makes it easy to handle. Note that the electro-conductive sheet  28  made of any combination of the above described layers can be realized at relatively low cost. Further, in case of abolishing the image forming apparatus, removal of the sheet portion only of the holder  30  allows the remaining resin substrate  25  to be utilized once again. At this time, if the electro-conductive sheet  28  is installed in the resin substrate  25  in such a manner as to be easily peeled off, it can be more easily utilized. 
   Incidentally, in the present embodiment, for the sake of simplicity, a location of the holder  30  is limited, but the location is essentially not to be limited. Further, in the present embodiment, though the image forming apparatus comprising four image forming sections was employed, it is not limited to this configuration. Further, in the present embodiment, though lead wires of the image forming means are connected to the power source or the substrate, the connecting point is not limited to this. 
   The foregoing embodiments are included merely to aid in the understanding of the invention. However, it is to be understood that the invention is not intended to be limited to the embodiments, and variations may be made by those skilled in the art without departing from the spirit and the scope of the invention.