Abstract:
A corona wire cartridge includes: a reel around which a corona wire is wound; a reel holder that rotatably supports the reel; a casing having a receiving portion which receives the reel and the reel holder and a wire drawing opening through which the corona wire is drawn; and an elastic member that movably connects the casing to the reel holder.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a corona wire cartridge for a corona discharger that is applied to a charger, a transcriber, and a static eliminator of an image forming apparatus. 
     2. Background Art 
     A corona discharger where high voltage is applied to an electrode having a wire shape, a corona wire, to generate corona discharging is applied to, for example, a charger, a transcriber, and a static eliminator of a printer or a copier that forms images by using an electrography process. 
     In the corona wire, discharging efficiency may be reduced or local discharging may occur due to oxidation coming from the discharging or deterioration coming from attachment of floating toners resulting from static electricity during the discharging, and nonuniform charging of an object to be charged (photoreceptor, intermediate transfer body, paper, and so on) incurs poor printing including nonuniform concentration of black lines, white lines, and images. 
     Therefore, it is necessary to regularly replace the corona wire, and a structure where the corona wire is easily replaced is proposed in, for example, JP-A-62-131274 
     SUMMARY OF THE INVENTION 
     JP-A-62-131274 discloses a corona wire cassette where corona wires are wound around a reel member having a spiral spring therein and drawn from a casing and wound into the casing. 
     Even though the above-mentioned configuration provides improved handling of the corona wires, it is disadvantageous in that since parts such as switch rollers or felt rings for providing the spiral spring into the reel member or guiding the corona wires from the casing are required, costs of parts and assembling are increased. 
     Additionally, tension is continuously applied to the corona wires in the casing due to the spring or a transverse load is applied to the corona wires due to the switch roller, causing inferior effects such as lengthening or cutting of the corona wires. 
     A corona wire cartridge includes: a reel around which a corona wire is wound; a reel holder that rotatably supports the reel; a casing having a receiving portion which receives the reel and the reel holder and a wire drawing opening through which the corona wire is drawn; and an elastic member that movably connects the casing to the reel holder. 
     According to an aspect of the invention, it is possible to provide a corona wire cassette that has reduced costs of parts and assembling due to the small number of parts. 
     Furthermore, it is possible to prevent corona wires from being lengthened and cut, as an unnecessary load is not applied to the corona wires. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention may be more readily described with reference to the accompanying drawings: 
         FIG. 1  is a sectional elevation view illustrating an internal configuration of a corona wire cartridge. 
         FIG. 2  is a sectional view taken in the direction of the arrow along the line A-A of  FIG. 1 . 
         FIG. 3  is a side view taken in the direction of the arrow B of  FIG. 1 . 
         FIG. 4  is a side view of a reel. 
         FIG. 5  is a sectional view illustrating another embodiment of the invention. 
         FIG. 6  is a view illustrating the provision of an end of a corona wire to a corona discharger. 
         FIG. 7  is a view illustrating a device for determining a position of the corona wire cartridge in relation to the corona discharger. 
         FIG. 8  is a view schematically illustrating an image forming apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is an elevation in section illustrating an internal configuration of a corona wire cartridge,  FIG. 2  is a sectional view taken in the direction of the arrow along the line A-A of  FIG. 1 ,  FIG. 3  is a side view taken in the direction of the arrow B of  FIG. 1 , and  FIG. 4  is a side view of a reel. 
     In  FIG. 1 , reference character W denotes a corona wire that has a diameter of about 0.06 mm and is formed of a tungsten wire, and reference numeral  31  denotes a reel around which the corona wire W is wound. As shown in  FIG. 4  where the reel  31  is seen in the opposite direction in relation to  FIG. 1 , the reel  31  has a thick portion  31   c  at a circumference thereof so that a recess  31   b  is formed around a reel shaft  31   a.    
     A radial groove  31   d  extending from the recess  31   b  to the circumference of the reel  31  is formed in a portion of a thick portion  31   c.    
     As to the reel  31  having the above-mentioned configuration, a wheel a that is provided at an end of the wire is hanged on the reel shaft  31   a  so that the corona wire W is supported by the reel  31 . A portion other than the end of the wire W is drawn from the groove  31   d  and wound around the circumference of the reel  31 . Meanwhile, an annular member b is provided at another end of the wire W. 
     Turning to  FIG. 1 , the reel  31  is supported by a reel holder  32 . As shown in  FIG. 2 , the reel  31  is inserted into the reel holder  32  and the reel shaft  31   a  is fitted into through holes  32   a  provided in the reel holder  32 , so that the reel  31  is rotatably supported by the reel holder  32 . 
     A receiving portion  33   a  is formed in a casing  33  of the corona wire cartridge to receive the reel  31  supported by the reel holder  32 , and the reel  31  and the reel holder  32  are provided in the receiving portion  33   a  like the arrangement of  FIG. 1 . 
     The connection between the reel holder  32  and the casing  33  is performed using a spring  34  extending between a protrusion  33   b  provided in the receiving portion  33   a  and the reel holder  32 . 
     Since the reel holder  32  is always biased by the spring  34  in the direction of the arrow x, the reel  31  is also drawn in the same direction due to the reel holder  32 . For this, the reel  31  is supported by inclined sides  33   c  provided in the receiving portion  33   a  to stop the drawing of the reel and to regulate the position of the reel  31  in the receiving portion  33   a , so that excessive force (excessive tension) is not applied to the corona wire W. 
     A supporting portion  33   e  is provided at a wire drawing opening  33   d  of the casing  33  to support an annular member b provided at the wire W. 
     As shown in  FIG. 6 , the annular member b which is provided at the wire W acts as a terminal hooked on a hook member  40   a  that is provided in a corona discharger  40  when the wire is provided into the corona discharger. In order to provide the wire W into the corona discharger  40 , first, the annular member b is hooked on the hook member  40   a  of the corona discharger. 
     Next, the cartridge longitudinally moves in relation to the corona discharger  40  to unwind the wire W. As shown in  FIG. 7 , the position of the cartridge that moves from an end of the corona discharger  40  to another end thereof is determined by a projection  40   c  that engages with a recess  33   f  provided on a side of the casing  33  and an engagement hook  40   d  hooked on a latch  33   g  at a cartridge mounting portion  40   b  provided in the corona discharger  40 . 
     Since the supporting portion  33   e  which supports the annular member b is provided to the casing  33  to stabilize the posture of the annular member b, it is easy to hook the annular member b on the hook member  40   a  of the corona discharger and the replacement of the wire W is efficiently performed. 
     Furthermore, since a piece  33   h  having the latch  33   g  is flexible, if the cartridge is to be separated from the corona discharger, an operator pushes the piece  33   h  counterclockwise in  FIG. 7  to unhook the latch  33   g  fastened with the engagement hook  40   d  of the corona discharger. 
     In the modification of the embodiment, as shown in  FIG. 5 , a through hole  33   i  may be formed in a side of the casing  33  facing the reel shaft  31   a  and a groove  31   e  for tools may be formed in the reel shaft  31   a.    
     According to the above-mentioned configuration, since the winding of the wire W around the reel  31  may be performed outside, the assembling of the cartridge is efficiently performed, and, even if the wire is loosened, the wire may be tightly wound outside. 
       FIG. 8  illustrates a laser beam printer on which a corona discharger equipped with the corona wire cartridge of the invention is mounted. 
     In  FIG. 8 , reference numeral  1  denotes a laser beam printer, and a photosensitive drum  21  starts to rotate in the direction of the arrow by printing initiation signal that is transmitted from a controller  22 . The photosensitive drum  21  rotates at the speed that is identical with a printing speed of the laser beam printer  1 , and continues to rotate until the printing is stopped. If the photosensitive drum  21  rotates, high voltage is applied to the corona charger  2  including the corona discharger provided with the corona wire cartridge of the invention to uniformly charge the surface of the photosensitive drum  21  so that, for example, positive charges, are uniformly formed on the surface. 
     A polygonal rotating mirror  3  starts to rotate immediately after power is supplied to the laser beam printer  1 , and rotates highly precisely at a constant speed while the power is supplied. A laser beam emitted from a light source  4  that is formed of a semiconductor laser and so on reflects from the polygonal rotating mirror  3  and is radiated through an fθ lens  5  onto the photosensitive drum  21  while scanning is performed. 
     If letter data or figure data converted into dot images are transmitted from the controller  22  to the laser beam printer  1  as on/off signal of the laser beam, portions onto which the laser beam is and is not radiated are formed on the surface of the photosensitive drum  21  to form the so-called electrostatic latent image. 
     When the photosensitive drum having the electrostatic latent image reaches a portion facing a developing device  6 , a toner is supplied to the electrostatic latent image so that the positively charged toner is absorbed by static electricity, thus forming toner images at a portion from which electric charges are removed by radiation of the laser beam onto the photosensitive drum  21 . 
     Paper  7  that continuously extends and is received in a paper hopper  11  is transported between the photosensitive drum  21  and a transcriber  10  by using a paper transportation tractor  8  in synchronization with the arrival of the toner images of printed data formed on the upper surface of the photosensitive drum  21  to a transcription position. Furthermore, the transcriber  10  is a kind of corona discharger which is equipped with the corona wire cartridge of the invention. 
     The toner images formed on the photosensitive drum  21  are absorbed on the paper  7  by using the transcriber  10  that provides electric charges having the polarity opposite to that of toner images on a rear side of the paper  7 . 
     Therefore, the paper  7  that is provided in the paper hopper  11  is transported through the paper transportation tractor  8 , the transcriber  10 , the paper transportation tractor  9 , and a buffer plate  24  to a fixing device  12 . After the paper  7  transported to the fixing device  12  is preheated by a preheating plate  13 , the paper  7  is transported while being heated and pressed by using a nip portion formed by a pair of fixing rollers that is formed of a heating roller  14  provided with a heater lamp  25  and a pressing roller  15  to fix the toner images on the paper  7  by fusing. 
     The paper  7  which has been already transported by using the heating roller  14  and the pressing roller  15  is moved to a stacker table  19  by using a transportation roller  16  and accordion-folded along a roulette due to the swing of a swing fin  17 . Furthermore, the folded paper is adjusted by using rotating paddles  18  and stacked on the stacker table  19 . A portion of the photosensitive drum  21  that passes a transcription position is cleaned by using a cleaning device  20 , and then waits for the next printing. 
     In  FIG. 8 , reference numeral  23  denotes a display screen that displays information regarding the state of the laser beam printer during the printing. The buffer plate  24  is used to compensate loosening or tightening of the paper  7  in the case of when there is a difference in paper transportation speed of the paper transportation tractor  9  and the fixing rollers  14  and  15 . Furthermore, reference numeral  26  denotes a web member that is capable of coming into contact with the surface of the heating roller  14  and being wound and is used to clean the surface of the heating roller  14  and apply a release agent on the surface of the heating roller  14 . 
     In the above-mentioned embodiment, a description is given of the application of the corona discharger provided with the corona wire cartridge of the invention to the charger  2  and the transcriber  10 . However, a corona static electricity remover may be provided to remove static electricity from a portion of the surface of the photosensitive drum  21  between the transcriber  10  and the cleaning device  20 , or a corona discharger for pre-electrification may be provided to perform pre-electrification of the surface of the photosensitive drum  21  between the cleaning device  20  and the charger  2 . In this connection, the invention may be applied to the corona static electricity remover and the corona discharger for pre-electrification.