Patent Publication Number: US-6711370-B2

Title: Liquid electrophotographic image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Application No. 2002-39151 filed Jul. 6, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid electrophotographic image forming apparatus, and more particularly, to a liquid electrophotographic image forming apparatus in which a developer, to develop an image formed on a photosensitive body and an ink reservoir to supply ink to the developer are formed monolithically. 
     2. Description of the Related Art 
     In general, electrophotographic image forming apparatuses form an electrostatic latent image on a photosensitive medium, such as a photosensitive drum or photosensitive belt, develop the electrostatic latent image by a developing agent of a predetermined color, and transfer the developed image onto a sheet of paper, thereby forming a desired image. 
     Such electrophotographic image forming apparatuses are classified into a dry type and a wet type according to the type of the developing agent. Dry type image forming apparatuses use toner in a powder state, while liquid image forming apparatuses use a liquid developing agent, in which the toner is mixed with a volatile liquid carrier. The liquid image forming apparatuses have better printing quality than the dry type image forming apparatuses and reduce the risks of health problems caused by harmful toner dust. 
     FIG. 1 schematically shows the structure of a conventional liquid color image forming apparatus. 
     Referring to FIG. 1, a plurality of image forming units are arranged serially along a circulation route of a transfer belt  40 , which moves on an endless track by a plurality of rollers  41 ,  42 , and  44 . Each of the image forming units transfers cyan (C), magenta (M), yellow (Y), and black (K) images, respectively, onto the transfer belt  40 . 
     Each image forming unit includes a photosensitive drum  30 , which transfers a toner image of a predetermined color onto the transfer belt  40 ; a charger  36 , which charges the surface of the photosensitive drum  30  at a predetermined electric potential; a laser scanning unit (LSU)  38 , which forms an electrostatic latent image by radiating light onto the charged surface of the photosensitive drum  30 ; a developing unit  10 , which develops the electrostatic latent image into a predetermined toner image; and a cleaning blade  32 , which removes a developing agent remaining on the photosensitive drum  30  after the developed toner image is transferred onto the transfer belt  40 . Reference numeral  34  denotes an eraser that erases an electric potential on the photosensitive drum  30 . 
     When the transfer belt  40  is supported and rotated by a driving roller  41 , a second transfer backup roller  44  and a plurality of first transfer backup rollers  42  corresponding to the photosensitive drum  30 , the image that is formed on the photosensitive drum  30  is transferred onto the transfer belt  40 . A second transfer roller  43  is installed to rotate in a direction opposite to the rotation of the second transfer backup roller  44 , and the transfer belt  40  is placed between the second transfer backup roller  44  and the second transfer roller  43 . The second transfer roller  43  transfers the image on the transfer belt  40  onto a sheet of paper  60 . 
     The paper  60  onto which the color image is transferred by the second transfer roller  43  is heated at a predetermined temperature and pressurized by a fusing unit  50  installed on a paper ejecting route, and the toner image is fixed on the paper  60 . 
     FIG. 2 shows a detailed diagram of the image forming unit of FIG.  1  and illustrates a magenta developing unit  10 -M among developing units having the same structure of FIG.  1 . 
     Referring to FIG. 2, the developing unit  10  includes a developing portion  11 , an ink reservoir  12  in which ink supplied to the developing portion  11  is stored, and a circulating portion  13  which circulates ink between the developing portion  11  and the ink reservoir  12 . 
     The developing portion  11  includes a developing container  14  in which a developing agent (hereinafter, referred to as ink) is stored; a developing roller  15 , part of which is dipped in the developing agent and installed to face the photosensitive drum  30 ; a depositing roller  16 ; a cleaning roller  17 ; and a metering roller  18 . 
     Part of the developing roller  15  is dipped in the developing agent stored in the developing container  14 . The depositing roller  16  is dipped in the developing agent stored in the developing container  14 , and a predetermined voltage is applied to the depositing roller  16  being spaced apart from the developing roller  15  by a predetermined gap. The depositing roller  16  deposits the developing agent onto the surface of the developing roller  15  utilizing a difference in an electric potential between the depositing roller  16  and the developing roller  15  having the predetermined voltage. 
     The metering roller  18  is installed to be adjacent to the developing roller  15  and regulates the developing agent placed on the developing roller  15  to a predetermined thickness. 
     An ink feed hole  19  and an ink exhaust hole  20  are provided in the developing container  14 . The circulating portion  13  includes an ink feed route  21  that connects the ink reservoir  12  to the ink feed hole  19  of the developing container  14 , and an ink withdrawal route  22  that connects the ink reservoir  12  to the ink exhaust hole  20  of the developing container  14 . A pump  23  is installed on the ink feed route  21 . 
     Ink withdrawn from the ink reservoir  12  by the pump  23  is supplied to the developing container  14  via the ink feed route  21  connected to the ink feed hole  19 . Since the developing agent in the developing container  14  is maintained at a uniform level, ink that exceeds this level is withdrawn to the ink reservoir  12  via the ink withdrawal route  22  connected to the ink exhaust hole  20 . 
     According to the above-mentioned structure, ink withdrawn from the ink reservoir  12  passes through the ink feed route  21 , the developing container  14 , and the ink withdrawal route  22 , back to the ink reservoir  12 . 
     However, according to the structure of FIG. 2, an additional ink reservoir  12  is needed to supply ink to the developing portion  11 , a hose is required to form an ink circulation route between the ink reservoir  12  and the developing container  14 , and the pump  23  is used to supply ink, thereby increasing the volume of the image forming apparatus. In addition, the hose may be clogged by ink. Thus, when replacing the hose or ink reservoir  12  with another one, it is difficult to attach and detach a coupler (not shown) to and from the hose or ink reservoir  12 , and accordingly, ink may leak out of the unit. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an aspect of the present invention to provide a liquid image forming apparatus in which a developing portion and an ink reservoir are formed monolithically and a unit to supply ink to the developing portion. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     The foregoing and/or other aspects of the present invention are achieved by providing a liquid image forming apparatus comprising: a developing portion in which a developing roller to develop an electrostatic latent image formed on a photosensitive body in a predetermined color is installed and which is maintained at a uniform level so that the developing roller is dipped at a predetermined level; an ink reservoir in which ink supplied to the developing portion is stored; and an ink supplying unit that supplies ink stored in the ink reservoir to the developing portion. The developing portion and the ink reservoir are provided in one developing container. The ink supplying unit includes a barrier wall by which the developing container is divided into the developing portion and the ink reservoir and a lower part of which is opened, and an ink supplying roller which is installed to contact the lower part of the barrier wall and a bottom surface of the developing container and supplies ink in the ink reservoir to the developing portion. 
     The ink supplying roller is compressed by a lower end of the barrier wall, passes through the lower end of the barrier wall, expands, absorbs ink in the ink reservoir, meets the lower end of the barrier wall and is compressed when rotating, and ejects ink in the developing portion. 
     The apparatus further includes a protrusion which projects to correspond to the ink supplying roller in a direction of the barrier wall and is formed to compress an outer surface of the ink supplying roller on the bottom surface of the developing container contacting the ink supplying roller, and wherein the ink supplying roller passes through the protrusion, expands, absorbs ink in the ink reservoir, meets the protrusion and is compressed when rotating, and ejects ink in the developing portion. 
     In an aspect of the invention, an elastic porous material is formed on the outer surface of the ink supplying roller. 
     The apparatus further includes a photosensitive drum on which an electrostatic latent image developed by the developing roller is formed, an eraser which erases an electric potential on the photosensitive drum, and an exposing unit which forms an electrostatic latent image on the erased photosensitive drum. The above elements are provided in the developing container and form a single image forming unit. 
     The foregoing and/or other aspects of the present invention may also be achieved by providing a liquid image forming apparatus comprising: a developing portion in which a developing roller that develops an electrostatic latent image formed on a photosensitive body in a predetermined color is installed and which is maintained at a uniform level so that the developing roller is dipped at a predetermined level, an ink reservoir in which ink supplied to the developing portion is stored, and an ink supplying unit that supplies ink stored in the ink reservoir to the developing portion. In an aspect of the present invention, the developing portion and the ink reservoir are provided in one developing container. The ink supplying unit includes a barrier wall by which the developing container is divided into the developing portion and the ink reservoir and a lower part of which is opened, a cylindrical casing, upper and lower parts of which are fixed between the lower part of the barrier wall and a bottom surface of the developing container, having openings at both sides formed to face the developing portion and the ink reservoir, respectively, an axis eccentric in the cylindrical casing, and a plurality of impellers, one end of each impeller being fixed on the eccentric axis. 
     In another aspect of the invention, the eccentric axis is eccentric in the casing in a direction of the developing portion. 
     In yet another aspect of the invention, the impellers are formed of elastic rubber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 schematically shows the structure of a conventional liquid color image forming apparatus; 
     FIG. 2 shows a detailed diagram of the image forming unit of FIG. 1; 
     FIG. 3 shows a developing unit of a liquid image forming apparatus according to an embodiment of the present invention; 
     FIG. 4 schematically shows the structure of an image forming unit in which the developing unit of FIG. 3, a photosensitive drum, an eraser, and a charger are formed monolithically; 
     FIG. 5 shows the structure of a developing unit of the liquid image forming apparatus according to another embodiment of the present invention; and 
     FIG. 6 shows the structure of a developing unit of the liquid image forming apparatus according to yet another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
     FIG. 3 shows a developing unit of a liquid image forming apparatus according to an embodiment of the present invention. The same names are used for the same elements as those in FIGS. 1 and 2, and the detailed descriptions thereof will be omitted. 
     Referring to FIG. 3, one barrier wall  120  is provided in a developing container  110  in which a developing agent is stored. The developing container  110  is divided into a developing portion  111  which develops a surface of a photosensitive drum  30  and an ink reservoir  112  in which ink supplied to the developing portion  111  is stored using the barrier wall  120 . 
     The developing portion  111  includes a developing roller  115  installed to face the photosensitive drum  30 , a depositing roller  116  which deposits a developing agent onto the surface of the developing roller  115 , a metering roller  118  which regulates the amount of ink stuck onto an outer surface of the developing roller  115 , and a cleaning roller  117 . 
     A lower part of the barrier wall  120  is opened, and an ink supplying roller  122  is installed between the lower part of the barrier wall  120  and the bottom surface of the developing container  110 . The ink supplying roller  122  in cooperation with the barrier wall  120  suppresses the flow of ink between the developing portion  111  and the ink reservoir  112 . The outer surface of the ink supplying roller  122  is covered with an elastic porous material, e.g., sponge. When the ink supplying roller  122  is rotated, the sponge is compressed by the lower end of the barrier wall  120 , as shown in FIG.  3 . After the compressed portion of the ink supplying roller  122  passes through the lower end of the barrier wall  120  toward the ink reservoir  112 , the compressed sponge is returned to its original state and absorbs ink in the ink reservoir  112 . When the ink supplying roller  122  rotates, the ink supplying roller  122  meets the lower end of the barrier wall  120 , and the sponge is compressed again, wherein the ink supplying roller  122  ejects and supplies ink to the developing portion  111 . 
     The level of ink in the developing portion  111  should be uniform so that only a predetermined part of the developing roller  115  is dipped in the ink of the developing portion  111 . Thus, a sufficient amount of ink should be supplied to the developing portion  111  by the ink supplying roller  122 , and ink which exceeds a predetermined level in the developing portion  111  is withdrawn to the ink reservoir  112  along the upper part of the barrier wall  120 . 
     The operation of the developing unit having the above structure will be described in detail with reference to the attached drawings. 
     The operation of the developing portion  111  will be described first. If an electrostatic latent image is formed on the photosensitive drum  30 , the developing roller  115  rotates and develops the electrostatic latent image in a predetermined color by ink placed onto the surface of the developing roller  115 . Subsequently, ink remaining on the surface of the developing roller  115  is removed by the cleaning roller  117 . Subsequently, ink on the depositing roller  116 , to which a predetermined voltage is applied, is transferred to the developing roller  115 . The rotating developing roller  115  meets the metering roller  118 , which removes excess ink from the developing roller  115 , while ink less than a predetermined thickness remains on the developing roller  115 . The remaining ink on the developing roller  115  performs a developing process. 
     Next, the operation of supplying ink to the developing portion  111  from the ink reservoir  112  will be described. From the bottom surface of the developing container  110 , the ink supplying roller  122  rotates in a direction of the developing portion  111  from the ink reservoir  112 . The rotating ink supplying roller  122  meets the lower end of the barrier wall  120  and is compressed to a predetermined depth, as shown in FIG.  3 . The compressed ink supplying roller  122  is rotated toward the ink reservoir  112 , is returned to its original state by a restoring force, and absorbs ink in the ink reservoir  112  into expanded pores. Subsequently, the ink supplying roller  122  again meets the lower end of the barrier wall  120 , where the pores are contracted when the ink supplying roller  122  is compressed, and the ink supplying roller  122  ejects ink into the developing portion  111 . Meanwhile, if a level of ink in the developing portion  111  is higher than the upper end of the barrier wall  120 , ink goes over the barrier wall  120 , and then is withdrawn to the ink reservoir  112 . Thus, the ink within developing portion  111  is maintained at a uniform level. 
     FIG. 4 schematically shows the structure of an image forming unit in which the developing unit of FIG. 3, a photosensitive drum, an eraser, and a charger are formed monolithically. The same reference numerals are used for the same elements as those in FIG. 3, and the detailed descriptions thereof will be omitted. 
     Referring to FIG. 4, in one cassette  140 , the following are arranged: a photosensitive drum  130 ; a charger  136 , which charges the photosensitive drum  130 ; a developing unit, which develops the electrostatic latent image; a cleaning blade  132 , which removes toner on the photosensitive drum  130  after a transfer operation onto a transfer body is completed; and a container  139  in which toner removed by the cleaning blade  132  is withdrawn. A laser scanning unit (LSU)  138 , which forms an electrostatic latent image on the charged photosensitive drum  130 , is placed at one side of the cassette  140 . The LSU  138  radiates light onto the photosensitive drum  130  via an open portion  140 a formed at the side of the cassette  140 . 
     Each of the above elements, except the LSU  138 , are formed inside one monolithic cassette  140 , and the cassette  140  can be replaced with another after being used for a predetermined amount of time. An opening  140   b  for the photosensitive drum  130  contacting the transfer body is formed at the other side of the image forming unit with respect to the open portion  140   a.  Thus, a plurality of image forming units to transfer color images onto the transfer body should be arranged in a vertical direction. 
     Further, although not shown, if the opening  140   b  is placed on the upper portion of the image forming unit, a plurality of image forming units can be arranged in a horizontal direction, as shown in FIG.  1 . 
     The operation of the above structure will be described in detail with reference to the attached drawings. 
     First, the charger  136  charges the photosensitive drum  130  to a predetermined potential. Subsequently, the LSU  138  forms an electrostatic latent image on the surface of the charged photosensitive drum  130  via the opening  140   a.  The electrostatic latent image is developed by the developing roller  115  in a predetermined color. The surface potential of the photosensitive drum  130  is removed by the eraser  134  after the developed image is transferred onto a transfer body (not shown). Subsequently, toner remaining on the surface of the photosensitive drum  130  is removed by the cleaning blade  132 , and then is withdrawn to the toner withdrawing container  139 . The operations of the other structures are the same as those in the above embodiment, and thus will be omitted. 
     FIG. 5 shows the structure of the developing unit of the liquid image forming apparatus according to another embodiment of the present invention. The same reference numerals are used for the same elements as those in FIG. 3, and the detailed descriptions thereof will be omitted. 
     Referring to FIG. 5, one barrier wall  120  is vertically installed in a developing container  110  in which a developing agent is stored. The developing container  110  is divided into a developing portion  111  which develops a surface of a photosensitive drum  30 , and an ink reservoir  112  in which ink supplied to the developing portion  111  is stored using the barrier wall  120 . 
     A lower part of the barrier wall  120  is opened, and an ink supplying roller  222  is installed between the lower part of the barrier wall  120  and the bottom surface of the developing container  110 . A protrusion  224 , projected to correspond to the ink supplying roller  222  in a direction of the barrier wall  120 , is formed on the bottom surface of the developing container  110  contacting the ink supplying roller  222 . The outer surface of the ink supplying roller  222  is covered with an elastic porous material, e.g., sponge. The sponge is compressed at a portion where the ink supplying roller  222  meets the protrusion  224 . The ink supplying roller  222  with the barrier wall  120  suppresses the movement of ink between the developing portion  111  and the ink reservoir  112 . When the ink supplying roller  222  rotates, the sponge is compressed by the protrusion  224 . After the compressed portion of the sponge passes through the protrusion  224 , the compressed portion is returned to its original state and absorbs ink of the ink reservoir  112 , thereby the ink supplying roller  122  ejects ink in the developing portion  111  when the portion of the ink supplying roller  122  is compressed. 
     The level of the developing portion  111  should be uniform so that only a predetermined part of the developing roller  115  is dipped in ink of the developing portion  111 . Thus, a sufficient amount of ink should be supplied to the developing portion  111  by the ink supplying roller  222 , and ink, which exceeds a predetermined level, is removed to the ink reservoir  112  along the upper part of the barrier wall  120 . 
     The operation of supplying ink to the developing portion  111  from the ink reservoir  112  of the developing unit according to the above embodiment will be described in detail with reference to the attached drawings. 
     From the bottom surface of the developing container  110 , the ink supplying roller  222  rotates in a direction of the ink reservoir  112  from the developing portion  111 . The rotating ink supplying roller  222  meets the protrusion  224  and is compressed to a predetermined depth. The compressed portion of the ink supplying roller  222  is returned to its original state by a restoring force in the ink reservoir  112  and absorbs ink in the ink reservoir  112  into expanded pores. Subsequently, the ink supplying roller  222  again meets the protrusion  224  where the pores are contracted when the ink supplying roller  222  is compressed, and the ink-supplying roller  222  ejects ink into the developing portion  111 . Meanwhile, if ink in the developing portion  111  exceeds a predetermined level, ink supplied excessively goes over the upper end of the barrier wall  120 , and then is withdrawn to the ink reservoir  112 . Thus, the developing portion  111  is maintained at a uniform level. 
     FIG. 6 shows the structure of the developing unit of the liquid image forming apparatus according to another embodiment of the present invention. The same reference numerals are used for the same elements as those in FIG. 3, and the detailed descriptions thereof will be omitted. 
     Referring to FIG. 6, a barrier wall  120  is vertically installed in a developing container  110  in which a developing agent is stored. The developing container  110  is divided into a developing portion  111 , which develops a surface of a photosensitive drum  30 , and an ink reservoir  112  in which ink supplied to the developing portion  111  is stored using the barrier wall  120 . 
     A lower part of the barrier wall  120  is opened, and an eccentric ink supplying pump  300  is provided between the lower part of the barrier wall  120  and the bottom surface of the developing container  110 . The eccentric ink supplying pump  300  includes a casing  302 , an eccentric axis  304 , and a plurality of impellers  306 . Upper and lower parts of the casing  302  are fixed at the lower end of the barrier wall  120  and inside the developing container  110 , respectively. Openings  307  and  308 , each of which faces the developing portion  111  and the ink reservoir  112 , respectively, are formed at opposite sides of the casing  302 . The eccentric axis  304  is eccentric in the casing  302  in a direction of the developing portion  111 . The plurality of impellers  306  equally spaced apart from one another are connected to the eccentric axis  304 . Preferably, the plurality of impellers  306  are formed of a flexible material, such as urethane rubber. 
     The operation of supplying ink to the developing portion  111  from the ink reservoir  112  of the developing unit according to the above embodiment will be described in detail with reference to the attached drawings. 
     When the ink supplying pump  300  rotates in a clockwise direction of FIG. 6, the impellers  306 , connected to the eccentric axis  304 , are bent to be opposite to a rotation direction in the casing  302 , seal the casing  302 , and rotate. The impellers  306  are spaced apart from one another by a uniform interval. The volume A between the two impellers  306  at the opening  308  having a large interval between the eccentric axis  304  and the casing  302  is larger than the volume B between the two impellers  306  at the opening  307  having a small interval between the eccentric axis  304  and the casing  302 . Thus, ink sucked between the two impellers  306  at the opening  308  connected to the ink reservoir  112  rotates such that at the opening  307  having a smaller volume between the two impellers  306 , ink of a difference between the volumes A and B is ejected to the developing portion  111 . Meanwhile, if ink in the developing portion  111  exceeds a predetermined level, ink supplied excessively goes over the upper end of the barrier wall  120 , and then is withdrawn to the ink reservoir  112 . Thus, the developing portion  111  is maintained at a uniform level. 
     As described above, in the liquid image forming apparatus according to the present invention, the developing portion and the ink reservoir are simply formed as one unit, and thus parts and space required for the circulating portion which circulates ink between the developing portion and the ink reservoir can be reduced, thereby simplifying the structure of a liquid printer and fundamentally solving clogging problems in the circulating portion. In addition, the image forming unit including the photosensitive drum is manufactured as one cassette, thereby easily being replaced with another one when a life span thereof is terminated. 
     Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.