Abstract:
A photosensitive drum protecting device for use in a color electrophotographic printer is provided. The printer, in which developing device cartridges of various colors including photosensitive drums and developing rollers are installed, and a printing path contacting the photosensitive drums is formed, includes a photosensitive drum protecting device that simultaneously exposes or protects each of the photosensitive drums. All of the photosensitive drums disposed at front end portions of the developing device cartridges are covered by just one photosensitive drum protecting device. Thus, the complexity of the printer is reduced and the printer can be made more compact.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 2003-51112, filed on Jul. 24, 2003, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference.  
         [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an electrophotographic printer. More particularly, the present invention relates to an electrophotographic printer with a simplified structure that facilitates further reduction in the size of the printer.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, electrophotographic printers print monochromatic or color images by scanning light onto a photosensitive medium charged to a predetermined potential to form an electrostatic latent image, developing the electrostatic image with toners of predetermined colors using a developer, and transferring and recording the developed image onto a physical recording medium such as a sheet of paper.  
         [0006]     Electrophotographic printers can be divided into liquid electrophotographic printers and dry-type electrophotographic printers according to the type of developer. A liquid electrophotographic printer uses a developer in which a powder toner is mixed with a liquid carrier. A dry-type electrophotographic printer uses a two-component developer including a powder carrier and a toner, or a single-component developer including a toner only. Hereinafter, the dry-type electrophotographic printer will be described, and the developer may be referred to as toner.  
         [0007]     In order to print a full-color image, different colored toners, such as yellow (Y), magenta (M), cyan (C), and black (K) colors are required. Thus, four developing devices that each develop one of the four color toners are required. To form a full-color image, there is a single path method, in which when a transfer substance passes through photosensitive substances, on which four color images are formed, the color images are sequentially transferred, and there is a multi-path method, in which when the transfer substance passes through the photosensitive substances, the image is transferred from only one photosensitive substance and the process is repeated to form the image. In both methods, the four developing devices are generally required.  
         [0008]     When a color image is printed using the multi-path method, the processing time is four times longer than when printing a monochromatic image, however, the structure of the printer is simple. When a color image is printed using the single-path method, the printing time is the same as when printing a monochromatic image, and thus color printing can be performed at a high speed.  
         [0009]      FIG. 1  is a cross-section of a conventional electrophotographic image forming apparatus using the single-path method, and  FIG. 2  is a cross-section of a developing device of the apparatus shown in  FIG. 1 .  
         [0010]     Referring to  FIG. 1 , the image forming apparatus includes a light scan unit  20  that scans light onto four photosensitive drums  10 , which are charged to a predetermined electric potential, to form an electrostatic latent image, four developing devices  30  that develop the electrostatic latent image with four color toners (Y, M, C, and K) to form toner images on the photosensitive drums  10 , a feeding belt  40  that conveys a sheet of paper onto which the toner images of four colors formed on the photosensitive drums  10  are transferred sequentially, and a fuser  50  that fuses the toner image onto the paper by heating and pressing the paper onto which the toner image has been transferred. A paper feeding cassette  60  that feeds the paper (S) is installed to be inserted/removed from a main body of the image forming apparatus. The photosensitive drums  10  are integrally installed on respective developing devices  30 , and the developing devices  30  including the photosensitive drums  10  are vertically disposed to perform a color printing operation according to the single-path method. This contributes to making the image forming apparatus compact.  
         [0011]     Referring to  FIG. 2 , which shows one of the developing devices  30  of the apparatus of  FIG. 1 , the photosensitive drum  10  is integrally installed on the developing device  30 . The developing device  30  includes the photosensitive drum  10 , a charging roller  31  that charges the photosensitive drum to a predetermined electric potential, a developing roller  32  that develops the electrostatic latent image on the photosensitive drum  10 , and a plurality of agitators  33  that mix and supply the toner in the developing device  30  to the developing roller  32 . Reference numeral  34  denotes a case of the developing device  30 , reference numeral  34   a  denotes an opening through which a laser beam passes to form the electrostatic latent image on the photosensitive drum  10 , and reference numeral  35  denotes a cleaning roller for removing toner remaining on the photosensitive drum  10 .  
         [0012]     The developing device  30  further includes a cover  71  that protects the photosensitive drum  10  from light and dust when the printer is opened to change a photosensitive drum  10  or clear a paper jam. Both ends of the cover  71  are connected to shafts  72 , and end portions of the shafts  72  are connected to levers  73 . The shaft  72  and the lever  73  are coupled by a hinge  74 , and the shaft  72  is connected to an spring  75 . Therefore, when the lever  73  rotates in the counterclockwise direction, the shaft  72  and the cover  71  also rotate in the counterclockwise direction to expose some part of the photosensitive drum  10 , so that the toner images can be transferred onto the paper placed on a paper feeding path. Also, when the lever  73  is released, the shaft  72  is drawn back to its original position by the spring  75  so that the cover  71  and the lever  73  rotate in the clockwise direction and the cover  71  protects the surface of the photosensitive drum  10 .  
         [0013]     However, in the color printer using the single-path method, in which the photosensitive drums  10  are vertically arranged using the four developing devices  30  (toner cartridges), a cover unit for protecting the photosensitive drum  10  is required for every toner cartridge. This takes up a lot of space and is a limitation to making the color printer compact.  
       SUMMARY OF THE INVENTION  
       [0014]     Embodiments of the present invention provide a compact color printer including a photosensitive drum protecting device having a simplified structure.  
         [0015]     According to an aspect of the present invention, there is provided a color electrophotographic printer, in which developing device cartridges of various colors including photosensitive drums and developing rollers are installed, and a printing path contacting the photosensitive drums is vertically formed, the printer including a photosensitive drum protecting device that simultaneously exposes/protects the photosensitive drums.  
         [0016]     The photosensitive drum protecting device may include a photosensitive drum cover including a plurality of elongated openings through which the photosensitive drums are exposed, a first elastic member that supports an upper portion of the photosensitive drum cover, a second elastic member that supports a lower portion of the photosensitive drum cover; and a protrusion that is installed between the photosensitive drum cover and one of the first elastic member or the second elastic member, in order to move the photosensitive drum cover along the printing path due to displacement of the protrusion.  
         [0017]     The photosensitive drum cover is fabricated using a flexible film, and may be fabricated using a polycarbonate film.  
         [0018]     When the protrusion is moved to a direction, the photosensitive drums may protrude from the elongated openings of the photosensitive drum cover to form a contact portion between the photosensitive drums and the printing path, and when the protrusion is moved to an original position, the photosensitive drum cover may block the contact portion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0020]      FIG. 1  is a cross-sectional view of a conventional color electrophotographic printer using a single-path method;  
         [0021]      FIG. 2  is a cross-sectional view of a developing device of the apparatus shown in  FIG. 1 ;  
         [0022]      FIG. 3  is a cross-sectional view of a color electrophotographic printer according to an embodiment of the present invention;  
         [0023]      FIG. 4  is a cross-sectional view of developing device cartridges of the apparatus shown in  FIG. 3 , wherein photosensitive drum protecting devices are in a open state; and  
         [0024]      FIG. 5  is a cross-sectional view of developing device cartridges of the apparatus shown in  FIG. 3 , wherein photosensitive drum protecting devices are in a closed state. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]      FIG. 3  shows a schematic configuration of a color electrophotographic printer according to an embodiment of the present invention.  
         [0026]     Referring to  FIG. 3 , developing device cartridges  130  that include photosensitive drums  110  and develop the photosensitive drums  110  with toners of yellow (Y), magenta (M), cyan (C), and black (K) colors are arranged in a direction perpendicular to a direction of a printing path. The photosensitive drum  110  contacts a sheet of paper on the printing path at a front end portion of each of the developing device cartridges  130 . A cleaning roller  135  that removes toner remaining on the drum  110 , a charging roller  131  that charges the photosensitive drum  110  to a predetermined electric potential, and a developing roller  132  that develops an electrostatic latent image formed on the surface of the photosensitive drum  110  by a light scanning unit  120  with toners of four colors (Y, M, C, and K) to form a toner image on the photosensitive drum  110  are disposed on each of the photosensitive drums  110 . A plurality of agitators  133  are installed inside the developing device cartridge  130  to stir the toner and supply the toner to the developing roller  132 .  
         [0027]     The light scanning unit  120  is disposed at a rear side of the developing device cartridges  130  to form the electrostatic latent images on the photosensitive drums  110  through openings (refer to  134   a  in  FIG. 4 ) formed in cases (refer to  134  in  FIG. 4 ) of the developing device cartridges  130 .  
         [0028]     A cassette  160  containing sheets of paper (S), and a pickup roller  180 , are disposed under the developing device cartridges  130 , and a paper feeding belt  140  is installed at a position facing the photosensitive drums  110  so that a sheet of paper (S) picked up by the pickup roller  180  proceeds along the printing path.  
         [0029]     A fuser  150  that heats and presses paper onto which images are transferred by the photosensitive drums  110 , to fuse the toner images on the paper, is disposed at a rear-end portion of the paper feeding path.  
         [0030]      FIG. 4  is a cross-section of developing device cartridges of the apparatus shown in  FIG. 3 , wherein photosensitive drum protecting devices are in a open state.  FIG. 5  is a cross-section of developing device cartridges of the apparatus shown in  FIG. 3 , wherein photosensitive drum protecting devices are in a closed state.  
         [0031]     Referring to  FIGS. 4 and 5 , the developing device cartridges  130  including the photosensitive drums  110  are vertically arranged, photosensitive drum covers  171  including openings  171   a  are disposed at front-end portions of the developing device cartridges  130 , and each opening  171   a  is installed to enable the corresponding photosensitive drum  110  to contact the paper on the printing path. An upper end of the photosensitive drum cover  171  is connected to a main body of the printer via a first spring  172 , and a lower end of the photosensitive drum cover  171  is connected to a protrusion  173 . The protrusion  173  is connected to a second spring  174  and movably connected to the printer main body. When the printer is operated or the printer main body is not opened, the second spring  174  is compressed by a unit (not shown) for pushing the protrusion  173  and the first spring  172  is extended. When the unit for pushing the protrusion  173  is released, the photosensitive drum cover  171  is moved upward by the recovery force of the first spring  172  and the second spring  174  to cover the front-end portion of the developing device cartridges  130  as shown in  FIG. 5 . In this way, the photosensitive drum cover  171  protects the surface of the photosensitive drum  110  from external light and dust. The opening  171   a  is shaped as a long hole appropriate for the photosensitive drum to protrude therethrough.  
         [0032]     The photosensitive drum cover  171  is fabricated using flexible film, such as polycarbonate film, for example, and the openings  171   a  are formed at positions corresponding to the center of photosensitive drums  110 .  
         [0033]     Operation of the color printer according to the above-described embodiment of the present invention will now be described with reference to the accompanying drawings.  
         [0034]     When the printer is performing a printing process or in a standby state, the protrusion  173  is pushed backward so that the photosensitive drum cover  171  is pushed a predetermined distance backward, enabling the photosensitive drums  110  to directly contact the printing path. Here, the first spring  172  is extended, and the second spring  174  is compressed. Since the openings  171   a  of the photosensitive drum cover  171  are positioned in front of the corresponding photosensitive drums  110 , the image forming process of the photosensitive drums  110  is performed as if there was no photosensitive drum cover  171 .  
         [0035]     When the photosensitive drum  110  is charged by the charging roller  131  to a predetermined electric potential, the light scanning unit  120  scans the surface of the photosensitive drum  110  to form an electrostatic latent image. If the developing device cartridges  130  are arranged in the order shown in  FIG. 3 , yellow color is developed first. The developing roller  132  of yellow color develops the electrostatic latent image on the photosensitive drum  110  to form a yellow toner image on the photosensitive drum  110 . The yellow toner image is transferred onto the paper (S) that enters the printing path as being laid on the paper feeding belt  140 . The paper onto which the yellow image is transferred receives the toner images formed on the photosensitive drums  110  sequentially. Therefore, toner images of four colors are overlapped on the paper when it passes by the photosensitive drums  110 . The paper with the toner images is heated and pressed by the fuser  150  to fuse the images on the paper. The paper on which the toner images are fused is then discharged from the printer.  
         [0036]     If the printer main body is opened to change the developing device cartridge  130  or fix a paper jam on the paper feeding path, the protrusion  173  is released and the first spring  172  and the second spring  174  are returned to their original positions. Accordingly, the photosensitive drum cover  171  connected to the springs  172  and  174  moves upward and the openings  171   a  are positioned between the photosensitive drums  110 . In this case, a front surface of the photosensitive drums  110  is protected from external light and dust by the photosensitive drum cover  171 .  
         [0037]     In the embodiment described above, the protrusion  173  is installed at the lower portion of the photosensitive drum cover  171 . However, in alternative embodiments, the protrusion  173  may be disposed at the upper portion of the photosensitive drum cover  171 , or any other suitable portion of the photosensitive drum cover  171 .  
         [0038]     Also, in the embodiment described above, the device for protecting the photosensitive drum is used in the developing device cartridge  130  including the photosensitive drum  110  at the front end portion thereof. However, the photosensitive drum protecting device can be used in a case where photosensitive drums are vertically arranged and corresponding respective developing devices are installed at one side of the photosensitive drums.  
         [0039]     In the color electrophotographic printer according to embodiments of the present invention, since all of the photosensitive drums that are disposed at the front portions of the developing device cartridges vertically arranged can be covered by one photosensitive drum protecting device, the number of elements in the printer can be reduced, and the printer can be made more compact.  
         [0040]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.