Patent Publication Number: US-8112018-B2

Title: Developing unit and an image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application and claims the benefit under 35 USC §120 of U.S. Ser. No. 11/390,348 filed Mar. 28, 2006 now abandoned which is hereby incorporated by reference in its entirety. This application also claims the benefit of Korean Patent Application No. 2005-84853 filed on Sep. 12, 2005, in the Korean Intellectual Property Office, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus. More particularly, the present invention relates to an improved developing unit for use in an image forming apparatus capable of developing an image by attaching a developer directly to an electrostatic latent image formed on an image carrying medium. The invention is also directed to an image forming apparatus including the developing unit. 
     2. Description of the Related Art 
     Conventional image forming apparatuses such as a laser printer, a laser emitting diode (LED) printer, a digital copier, and a general paper facsimile, perform the printing function by transferring an image signal in accordance with an input digital signal onto a printing medium in the form of a visible image. 
     Such image forming apparatuses include the image carrying medium, a developing unit, a laser scanning unit, and a fixing unit. 
     The image carrying medium is rotatably mounted in a main body of the image forming apparatus. An electrostatic latent image is formed on a surface of the image carrying medium by a laser beam projected from the laser scanning unit. The electrostatic latent image is visualized by toner supplied through the developing unit. Generally, the toner used herein has a predetermined color and electric property. The fixing unit fuses on the printing medium the visible toner image formed on the image carrying medium which is then transferred onto the printing medium by applying heat and pressure. 
     The developing unit comprises a developing unit body, a developing roller mounted in the developing unit body to supply the toner to the image carrying medium, a toner supplying roller, and an auger. The developing roller applies the toner supplied into the developing unit body to the electrostatic latent image by a predetermined thickness. Control of the toner thickness is provided by the developing unit body having a doctor blade for controlling the thickness of the toner layer supplied to the surface of the developing roller. The toner supplying roller and the auger supply the developing roller with the toner supplied to the developing unit body. 
     The above-structured developing unit is usually provided as a separate part from the image carrying medium and therefore has a relatively long lifespan since it can be used until the developing roller expires. Accordingly, a detachable toner cartridge has been suggested to refill the toner by replacing the toner cartridge. The auger and the toner supplying roller continuously supply the toner from the toner cartridge to the developing roller. 
     In the above-structured developing unit, however, a dedicated support member is required for mounting of the doctor blade to the developing unit body, thereby increasing the whole size of the developing unit. 
     In addition, in the conventional developing unit as described above, the toner may not be evenly supplied along the length of the developing roller. The toner can be concentrated and condensed at both ends of the toner supplying roller. When the condensed toner is supplied to the image carrying medium, quality of a finally printed image deteriorates. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to overcome the above problems and/or disadvantages. The invention also provides advantages that are not found in the prior devices as discussed hereinafter. Accordingly, an aspect of the present invention is to provide a developing unit having a simplified structured and an improved toner supply. The invention is further directed to an image forming apparatus including the developing unit of the invention. 
     In order to achieve the above-described aspects of the present invention, a developing unit is provided comprising a developing unit body having a toner inlet; a developing roller mounted in the developing unit body; a toner feeding unit for feeding charged toner through the toner inlet to the developing roller; and a doctor blade controlling thickness of the toner supplied to the developing roller, wherein the doctor blade is integrally formed with the developing unit body. 
     The developing unit body comprises a main frame for receiving the developing roller and the toner feeding unit, and has an open upper surface. The developing body also includes a cover frame covering the upper surface of the main frame and having a doctor blade. 
     The main frame and the doctor blade are formed of metal and attached to each other by welding. 
     The toner feeding unit comprises a toner supplying roller for supplying the toner to the developing roller; a pair of augers circulating the toner supplied to the developing unit body through the toner supplying roller; and a toner feeding member for feeding the charged toner through the toner inlet to one of the augers. 
     The toner feeding member includes a toner feeding belt running in association with one of the augers. 
     The developing unit body further comprises a protruded rib formed on a bottom and a ceiling thereof, respectively, to separate the pair of augers from each other and thereby form a toner circulation path. 
     The protruded ribs are integrally formed with the developing unit body. 
     Another aspect of the present invention is to provide an image forming apparatus comprising an image carrying medium mounted in a main body of the image forming apparatus; a developing unit for developing an electrostatic latent image by attaching developer to an area corresponding to the electrostatic latent image formed on the image carrying medium; a transfer unit for transferring the image developed on the image carrying medium onto a printing medium; and a fixing unit for fixing the transferred image on the printing medium. The developing unit comprises a developing unit body having a toner inlet; a developing roller mounted in the developing unit body; a toner feeding unit for feeding toner through the toner inlet to the developing roller; and a doctor blade for controlling thickness of the toner supplied to the developing roller and integrally formed with the developing unit body. 
     These and other features of the invention will become more apparent from the following detailed description of the invention in conjunction with the annexed drawings which disclose various embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above aspects and other features of the present invention will become more apparent by the detailed description of the exemplary embodiments thereof with reference to the attached drawing figures, wherein; 
         FIG. 1  is a schematic view showing an image forming apparatus according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional side view of the image forming apparatus according to an embodiment of the present invention; and 
         FIG. 3  is a cross-sectional top view of the image forming apparatus of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawing figures. 
     In the following description, same drawing reference numerals are used for the same elements in the different drawings. The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the invention but are not intended to limit the scope of the invention. Thus, it is apparent that the present invention can be carried out without those defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
     Referring to  FIG. 1 , an image forming apparatus according to an embodiment of the present invention, for producing a color image, comprises a main body  10 , an image carrying medium  20  mounted in the main body  10 . A plurality of developing units  30  attaching a developer to the image carrying medium  20  are provided. A transfer unit  40  for transferring an image formed on the image carrying medium  20  to a printing medium  11  is positioned adjacent the image carrying medium  20 . A fixing unit  50  for fixing the transferred image on the printing medium  11  by applying heat and pressure is positioned downstream of the transfer unit  40 . 
     A surface of the image carrying medium  20  is electrified to a predetermined potential by a charging unit (not shown) as known in the art. An electrostatic latent image corresponding to each color image is formed on the surface of the image carrying medium  20  through a laser beam projected by a laser scanning unit (not shown). 
     The plurality of developing units  30  sequentially attach color toners (black, cyan, magenta, and yellow) on the image carrying medium  20 . 
     The transfer unit  40  comprises a transfer belt  43  supported by a plurality of support rollers  41 . The transfer belt  43  moves along a caterpillar track defined by the rollers  41  and receive the color image from the surface of the image carrying medium  20 . The belt  43  contacts the image carrying medium  20  and the printing medium  11  and transfers the color image onto the printing medium  11  that is passing between and in contact with a transfer roller  45  and the belt  43 . 
     The fixing unit  50  comprises a heating roller  51  and a pressing roller  53  to fix the toner image transferred onto the printing medium  11  by applying heat and pressure. After passing through the fixing unit  50 , the printing medium  11  is discharged to the outside of the main body  10  with the image fixed thereon. 
     As shown in  FIGS. 2 and 3 , the developing unit  30  comprises a developing unit body  31 , a developing roller  32  rotatably mounted to the developing unit body  31 , and a toner feeding unit  33  for moving the toner supplied from a toner cartridge  60  to the developing roller  32 . 
     The developing unit body  31  comprises a main frame  31   a  accommodating the developing roller  32  and the toner feeding unit  33 . A cover frame  31   b  is connected to an upper end of the main frame  31   a  to close the body  31 . A toner inlet  31   c  directs the toner from the toner cartridge  60  to the toner feeding unit  33 . The main frame  31   a  is preferably formed from molded plastic. The upper part of the main frame  31   a  has an open top end and closed by the cover frame  31 . A first protruding rib b 1  is formed on a bottom of the main frame  31   a  by a predetermined height and is positioned between augers  35 ,  36  of the feeding unit  33 . The first protruding rib b 1  has a height that is shorter than the diameter of the developing roller  32  as shown in  FIG. 2 . 
     The cover frame  31   b  is provided with a doctor blade  31   d  contacting the developing roller  32  for controlling the thickness of the toner supplied onto the surface of the developing roller  32 . The doctor blade  31   d  extends from an end of the cover frame  31   b  to an upper surface of the developing roller  32  opposite the bottom portion of the main frame  31   a . The cover frame  31   b  is connected to the main frame  31   a  by a fastening member such as a bolt to cover the upper part of the main frame  31   a . The cover frame  31   b  may be formed of metal. Preferably, the doctor blade  31   d  is also formed of metal and attached to the cover frame  31   b  by welding. It will be understood that the cover frame  31   b  and the doctor blade  31   d  may be formed as an integrated unit made of metal. The doctor blade  31   d  is typically a thin resilient plate that is able to form a substantially uniform layer of toner on the developing roller  31   d.    
     The developing roller  32  is mounted to rotate in the vicinity of the image carrying medium  20  with a predetermined developing gap formed between the developing roller  32  and the image carrying medium  20 . While rotating, the developing roller  32  rotates with respect to the image carrying medium  20  to transfer the toner to the developing roller  32  to a predetermined thickness. 
     A second protruding rib b 2  having a predetermined height extends downward from a lower surface of the cover frame  31   b  toward and opposing the first protruding rib b 1 . The protruding ribs b 1  and b 2  are positioned between and separate augers  35  and  36  from each other, as described in detail hereinafter, to improve the flow of the toner. 
     The toner inlet  31   c  is formed at the upper end of the developing unit body  31 . The toner cartridge  60  is mounted to the toner inlet  31   c  for supplying the toner to the developing unit  30 . 
     The toner feeding unit  33  comprises a toner supplying roller  34  mounted within the developing unit body  31 , first and second augers  35  and  36 , and a toner feeding member  37 . 
     The toner supplying roller  34  is rotatably mounted in the vicinity of the developing roller  32 . The toner supplying roller  34  carries the toner supplied by the first and the second augers  35  and  36 , to the developing roller  32 . 
     The first and the second augers  35  and  36  are arranged parallel with the toner supplying roller  34  and rotate in opposite directions to each other. By rotation of the first and the second augers  35  and  36  in the opposite directions with the protruded ribs b 1  and b 2  interposed therebetween, the toner fed by the toner feeding member  37  is circulated along the toner circulation path formed by the augers  35  and  36  and supplied to the toner supplying roller  34 . The first auger  35  moves the toner fed from the toner feeding member  37  in a direction indicated by arrow A shown in  FIG. 3 . The toner being moved along the direction A is supplied to one end of the second auger  36 . The second auger  36  moves the toner delivered from the first auger  35 , in an opposite direction indicated by arrow B as shown in  FIG. 3 . A portion of the toner moving in the direction B is supplied to the developing roller  32  by the toner supplying roller  34 . The remaining portion of the toner that is not supplied to the developing roller  32 , is returned to the first auger  35  and re-circulated together with new toner supplied by the feeding member  37 . In the embodiment shown, the feeding member  37  is a belt. 
     As shown in  FIGS. 2 and 3 , the first rib b 1  and the second rib b 2  are positioned to oppose each other and define a gap therebetween to allow a limited amount of the toner to pass between the augers. The ribs b 1  and b 2  as shown in  FIG. 3  have a length less than the width of the body  31 . The ends of the ribs b 1  and b 2  are spaced from the side walls so that rotation of the augers enables the toner particles to flow in a substantially continuous path indicated by the arrow  62  in  FIG. 3 . 
     The first and the second protruded ribs b 1  and b 2  between the first and the second augers  35  and  36  enable the toner circulation path between the first and the second augers  35  and  36  to be clearly defined between the two augers  35  and  36 . Therefore, the toner is prevented from directly moving from the supply inlet  31   c  to the toner supplying roller  34  in a path transverse to the directions A and B. As a result, concentration and condensation of the toner at both ends of the toner supplying roller  34  can also be prevented. 
     The toner feeding member  37  comprises a feeding belt running along the length of the developing unit body  31 . The feeding belt is supported by the first auger  35  and a supporting roller  38  to move the toner charged through the toner inlet  31   c  to the first auger  35 . The feeding belt is rotated by the auger  35  and guided by guide protrusions  35   a  formed on the first auger  35 . 
     In the above developing unit  30 , the first and the second augers  35  and  36  are associated with the toner supplying roller  34  through a gear. The augers  35  and  36 , and the toner supplying roller  34  are rotated by power transmitted from the developing roller  32 . 
     The operation of the image forming apparatus having the above configuration according to an embodiment of the present invention will now be described. 
     First, a predetermined color image is formed on the image carrying medium  20  by the charging unit, the laser scanning unit, and the developing units  30 . The color image formed on the image carrying medium  20  is transferred onto the transfer belt  43 . The color image on the transfer belt  43  is then transferred onto the printing medium  11  being passed over the transfer roller  43 . After being passed through the fixing rollers  51   53  of the fixing unit  50 , the printing medium  11  is discharged from the main body  10 . 
     During the above printing processes, the toner is supplied from the toner cartridge  60  into the developing unit body  31  by the developing unit  30 . The supplied toner is moved to the first auger  35  by the toner feeding member  37 , for example, the feeding belt. The first auger  35  supplies the toner to one end of the second auger  36  in the direction A. The second auger  36  supplied with the toner at one end by the first auger  35  moves the toner in the direction B. A portion of the toner being moved in the direction B is supplied to the developing roller  32  by the toner supplying roller  34 . The remainder of the toner being moved in the direction B is carried by the second auger  36  and returned to the first auger  35 . The first auger  35  carries the toner returning from the second auger  36  and the toner fed by the feeding belt in the direction A again and keeps circulating the toners. 
     As described above, since the first and the second augers  35  and  36  supply the toner to the toner supplying roller  34  while continuously circulating the toner, the toner can be evenly supplied onto the toner supplying roller  34  without being concentrated at certain parts of the toner supplying roller  34 . In particular, by clearly defining the toner circulation path between the protruding ribs b 1  and b 2  formed between the first and the second augers  35  and  36 , the toner is prevented from being directly moved from the inlet  31   c  to the toner supplying roller  34  at the middle part, thereby improving the flow of the toner. Accordingly, condensation and deterioration of the toner is reduced. Finally, the quality of the printed image can be improved. 
     According to the above description, the doctor blade  31   d  is attached to the cover frame by welding so as to also function as the cover. Therefore, a dedicated bracket is not required to provide a compact size of the developing unit. 
     As a result, in case of a color image forming apparatus comprising a plurality of the developing units, the whole size of the apparatus can be reduced. 
     In addition, by providing the protruding ribs directed toward each other between the main frame and the cover frame, the strength of the frames is increased and the toner circulation path can be clearly defined between the augers. Therefore, being circulated inside the developing unit body by the augers, the toner is prevented from concentrating at both ends of the toner supplying roller or deteriorated. As a result, electrification performance of the toner and deterioration of the image quality is prevented. 
     While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.