Abstract:
In an image-forming device including an image-carrying member, a developer-carrying member, and a casing having an inner space in which developer is accommodated and the developer-carrying member is supported, both a pushing force and a separating force are not applied to the casing so that the thickness of the casing does not need to be increased. The casing is formed with a pair of first protruding parts each having an end that protrudes outward along the axial direction of the developer-carrying member, and a pair of second protruding parts each having an end that protrudes farther outward than the corresponding end of the first protruding part. The first protruding parts serve as operating parts operated by the pressing member, and the second protruding parts serve as operating parts operated by the separating member.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from Japanese Patent Application No. 2005-232158 filed Aug. 10, 2005. The entire content of each of these priority applications is incorporated herein by reference.  
       TECHNICAL FIELD  
       [0002]     The present invention relates to an electrophotographic image-forming device, such as a laser printer, a photocopier, or a facsimile device. The present invention also relates to a developing unit provided in the image-forming device.  
       BACKGROUND  
       [0003]     Laser printers described in Japanese Patent Application Publication Nos. HEI-11-133730 and 2005-37680 and also U.S. Pat. No. 6,751,428 are generally configured of a frame including a photosensitive drum, and a developing unit, commonly called a developer cartridge that is detachably mounted in the frame. The developer cartridge also includes a developing roller, and a case for accommodating developer. The case has an elongated shape that extends along the axial direction of the developing roller. The developing roller is positioned at a side surface of the case that extends along the axial direction of the developing roller. This type of laser printer also includes a pressing member for pressing the case so that the developing roller is pressed against the photosensitive drum in the frame, and a separating member for moving the case so that the developing roller separates from the photosensitive drum. This type of laser printer has been configured to apply both a pushing force with the pushing member for pushing the case of the developing unit and a separating force with the separating member for displacing the developing unit in a direction away from the photosensitive drum to single points on the case.  
         [0004]     However, when these forces are applied to the same points on the developer case, it is necessary to reinforce the part of the case to which the force is applied and the vicinity thereof. To avoid this problem, U.S. Pat. No. 6,546,218 proposes a laser printer that divides the load so that the force of pushing the case with a pushing member and the force for separating the case with a separating member are not applied to the same point.  
         [0005]     However, this type of load separating laser printer is configured so that the region near the longitudinal center of the developer case is pushed. Since there is potential for bending in the case with this construction, it is necessary to reinforce the laser printer by increasing the thickness of the case and the like.  
       SUMMARY  
       [0006]     In view of the foregoing, it is an object of the present invention to provide an image-forming device that does not apply both a pushing force and a separating force to the case of a developing unit and that does not require the thickness of the case to be increased.  
         [0007]     It is another object of the present invention to provide a developing unit employed in the image-forming device.  
         [0008]     To achieve the above and other objects, there is provided an image-forming device that includes an image-carrying member having a surface on which electrostatic latent images are formable; a developer-carrying member; a casing having an inner space configured to accommodate developer, a pressing member and a separating member. The developer-carrying member is configured to supply developer to the image-carrying member to develop the electrostatic latent image into a visible image. The developer-carrying member is supported in the casing and disposed in a position where developer accommodated in the inner space of the casing is conveyable to the image-carrying member. The pressing member is configured to press the casing in a direction causing the developer-carrying member to press against the image-carrying member. The separating member is configured to displace the casing in a direction that separates the developer-carrying member from the image-carrying member. The casing includes a pair of first protruding parts each having an end that protrudes outward along the axial direction of the developer-carrying member; and a pair of second protruding parts each having an end that protrudes farther outward than the corresponding end of the first protruding part, such that the first protruding parts serve as operating parts operated by the pressing member, and the second protruding parts serve as operating parts operated by the separating member.  
         [0009]     It is desirable that the second protruding parts and the operating parts are offset from each other in this image-forming device. Accordingly, forces in reverse directions are not repeatedly applied to the same region. Hence, unlike conventional developing units, this image-forming device makes it possible to construct a developing unit, without reinforcing parts at which the second protruding parts and operating parts are provided.  
         [0010]     According to another aspect of the invention, there is provided a developing unit that includes a developer-carrying member configured to supply developer to an image-carrying member on which electrostatic latent images are formable to develop the electrostatic latent image into a visible image; and a casing having an inner space configured to accommodate developer. The developer-carrying member is supported in the casing and disposed in a position where developer accommodated in the inner space of the casing is conveyable to the image-carrying member. The casing includes a pair of first protruding parts each having an end that protrudes outward along the axial direction of the developer-carrying member; and a pair of second protruding parts each having an end that protrudes farther outward than the corresponding end of the first protruding part, such that the first protruding parts serve as operating parts operated by the pressing member, and the second protruding parts serve as operating parts operated by the separating member. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a side cross-sectional view showing the general structure of a laser printer  1  serving as the image-forming device in the preferred embodiment;  
         [0012]      FIG. 2  is a cross-sectional view illustrating an operation for removing a frame  21  from the laser printer  1  in  FIG. 1 ;  
         [0013]      FIG. 3A  is a side view and  FIG. 3B  a front view of a developing unit according to the preferred embodiment;  
         [0014]      FIG. 4  is a perspective view of a block  21   a  constituting part of the frame  21  according to the preferred embodiment;  
         [0015]      FIG. 5  is a side view of the block  21   a  illustrating an operation for mounting a developing unit  22  on the block  21   a;    
         [0016]      FIG. 6  is an enlarged view of part of the side cross-sectional view in  FIG. 1  around the developing unit  22  and a developing roller  26  illustrating how a pressing member  70  presses against the developing unit  22 ;  
         [0017]      FIG. 7  is an enlarged view of part of the side cross-sectional view in  FIG. 1  around the developing unit  22  and a developing roller  26  illustrating how a separating member  80  separates the developing unit  22  from a photosensitive drum  30 ; and  
         [0018]      FIG. 8A  is a side view and  FIG. 8B  a front view illustrating a variation of the developing unit in the preferred embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0019]     An image forming device according to some aspects of the invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description.  
         [0020]      FIG. 1  is a side cross-sectional view showing the general structure of a laser printer  1  serving as the image-forming device.  FIG. 2  is a side cross-sectional view illustrating an operation for removing an image-forming unit  20  from the laser printer  1 .  
         [0021]     As shown in  FIG. 1 , the laser printer  1  is a direct tandem type color laser printer having four photosensitive drums  30  corresponding to the colors black, cyan, magenta, and yellow. The laser printer  1  includes a main casing  2  and, within the main casing  2 , a feeding unit  4  for feeding sheets of a paper  3 , the image-forming unit  20  for forming images on the paper  3  supplied from the feeding unit  4 , and a paper-conveying unit  35  for conveying the paper  3  along the image-forming unit  20 . In the following description, left and right sides and directions will conform to the left and right sides and directions in  FIG. 1 .  
         [0022]     A top cover  6  capable of opening and closing over the main casing  2  is provided on the top of the main casing  2 . In a closed position shown in  FIG. 1 , the top cover  6  covers the top surface of the main casing  2  in a substantially horizontal orientation. From the closed position, the top cover  6  can be pivotally rotated about hinges (not shown) provided in the main casing  2  to an open position by moving the left end of the top cover  6  upward. When the top cover  6  is in the open position, the image-forming unit  20  described later can be pulled out of the main casing  2  as indicated by an arrow in  FIG. 2 . When the top cover  6  is in the closed position, the top cover  6  is nearly flush with the top surface of the main casing  2 , as shown in  FIG. 1 .  
         [0023]     The feeding unit  4  includes a paper tray  7  that is detachably mounted in a lower section of the main casing  2 , a feeding roller  8  and a separating pad  9  disposed above a left end of the paper tray  7 , a pickup roller  10  disposed on the right of the feeding roller  8 , a pair of paper dust rollers  11  disposed above and to the left of the feeding roller  8 , and a pair of registration rollers  12 A and  12 B disposed above the paper dust roller  11 .  
         [0024]     The paper tray  7  is formed in a box shape having an open top for loading sheets of paper  3  and a depth capable of accommodating a fixed number of sheets of paper  3  in a stacked state. A left wall  13  is provided on the left end of the paper tray  7  and on the left surface of the main casing  2  below the top cover  6 . By pulling the left wall  13  leftward, it is possible to remove the paper tray  7  from the left side of the main casing  2  in a horizontal motion. A paper pressing plate  7 A is provided in the bottom surface of the paper tray  7  for supporting the paper  3  in a stacked state. The paper pressing plate  7 A is rotatably supported on the right end thereof, while the left end is urged upward by a spring (not shown). With this configuration, the left edge of the paper  3  stacked in the paper tray  7  is constantly urged upward.  
         [0025]     The urging force of the paper pressing plate  7 A presses the topmost sheet of paper  3  in the paper tray  7  toward the pickup roller  10 . During a printing operation, the pickup roller  10  rotates to begin conveying the topmost sheet toward a position between the feeding roller  8  and the separating pad  9 . As the sheet of paper  3  becomes interposed between the feeding roller  8  and the separating pad  9 , the rotating feeding roller  8  separates and conveys the paper  3  one sheet at a time. The paper dust rollers  11  receive and convey the sheet of paper  3  toward the registration rollers  12 A and  12 B while removing paper dust from the sheet.  
         [0026]     The registration rollers  12 A and  12 B are a drive roller and a follow roller, respectively. After adjusting the registration of the paper  3 , the registration rollers  12 A and  12 B convey the paper  3  along a paper-conveying path  14  and onto a conveying belt  38  in the paper-conveying unit  35  described later. The paper-conveying path  14  is an arc-shaped path formed in a frame  21  of the image-forming unit  20  described later.  
         [0027]     A scanning unit  18  is disposed in the topmost section of the main casing  2 . The scanning unit  18  irradiates four laser beams L based on prescribed image data for each color over surfaces of the corresponding photosensitive drums  30  described later in a high-speed scan. The scanning unit  18  emits the four laser beams L diagonally downward and to the right through the bottom surface of the scanning unit  18 . The laser beams L form parallel optical paths spaced at prescribed intervals in the left-to-right direction.  
         [0028]     An accommodating section  19  is formed inside the main casing  2  below the scanning unit  18  for accommodating the image-forming unit  20  so that the image-forming unit  20  can be mounted in and removed from the accommodating section  19  through the upper open portion of the main casing  2 . The image-forming unit  20  includes the frame  21 , mentioned above, that functions to retain the photosensitive drums  30 , Scorotron chargers  50 , developing units  22 , and cleaning brushes  33  provided for each color.  
         [0029]     The four developing units  22  are detachably mounted in the frame  21  and correspond to the colors black, cyan, magenta, and yellow, respectively. Each developing unit  22  includes a case  23  having a box shape open on the bottom side, and is formed with a toner-accommodating chamber  24  in the upper section of the case  23  that is filled with the corresponding color of toner. An agitator (not shown) is disposed inside the toner-accommodating chamber  24 . When the driving force of a motor (not shown) is inputted, the agitator rotates and stirs toner inside the toner-accommodating chamber  24 . A developing roller  26  is disposed on the lower side of the toner-accommodating chamber  24 .  
         [0030]     The developing roller  26  is rotatably supported in the case  23  of the developing unit  22  and is positioned in contact with the corresponding photosensitive drum  30  when the developing unit  22  is mounted in the frame  21 . The developing roller  26  includes a metal roller shaft that is covered with a roller member formed of an electrically conductive urethane rubber or silicon rubber containing fine carbon particles or the like. The surface of the roller member is also coated with a urethane rubber or silicon rubber containing fluorine. During a developing operation, a developing bias is applied to the developing roller  26 . Further, a motor (not shown) inputs a driving force for rotating the developing roller  26 .  
         [0031]     Toner discharged from the toner-accommodating chamber  24  is supplied to the developing roller  26  by a supply roller (not shown) provided in the toner accommodating chamber  24 . At this time, the toner is positively tribocharged between the supply roller and the developing roller  26 . A thickness-regulating blade (not shown) disposed in the toner-accommodating chamber  24  regulates the toner supplied on the developing roller  26  to maintain a thin layer of uniform thickness on the surface of the developing roller  26 .  
         [0032]     The photosensitive drum  30  is formed in a cylindrical shape and includes a main roller body  30 A and a metal roller shaft  30 B. The outermost surface of the main roller body  30 A is formed of a positive charging photosensitive layer such as polycarbonate. The metal roller shaft  30 B extends in the longitudinal direction of the main roller body  30 A through the axial center thereof. By rotatably supporting the metal roller shaft  30 B in the frame  21 , the photosensitive drum  30  can rotate with the metal roller shaft  30 B. Further, a motor (not shown) inputs a driving force for rotating the photosensitive drum  30 .  
         [0033]     Each charger  50  includes a charging wire  52  and is disposed in opposition to the corresponding photosensitive drum  30  at a prescribed distance so as not to contact the photosensitive drum  30  and so the charging wire  52  is positioned diagonally above and rightward of the photosensitive drum  30 . The charging wire  52  generates a corona discharge for charging the surface of the photosensitive drum  30  with a uniform positive polarity.  
         [0034]     Each cleaning brush  33  opposes and contacts the corresponding photosensitive drum  30  on the right side thereof.  
         [0035]     The paper-conveying unit  35  is disposed below the image-forming unit  20  when the image-forming unit  20  is mounted in the accommodating section  19 . The paper-conveying unit  35  includes a pair of belt support rollers  36  and  37  disposed on a right side and left side, respectively, and arranged parallel to each other, and a conveying belt  38  looped around the belt support rollers  36  and  37 . When the belt support roller  36  on the right side is driven to rotate by the driving force of a motor (not shown), the conveying belt  38  moves in a circuit around the belt support rollers  36  and  37 . Four transfer rollers  39  are disposed inside the conveying belt  38  at fixed intervals in the left-to-right direction. At these positions, the transfer rollers  39  oppose the respective photosensitive drums  30  with the conveying belt  38  interposed therebetween. A cleaning roller  40  is also disposed on the bottom of the conveying belt  38  for cleaning residual toner from the surface of the conveying belt  38 . A sheet of paper  3  conveyed from the registration rollers  12 A and  12 B along the paper-conveying path  14  contacts the top surface of the conveying belt  38  near the left edge thereof. At this time, the conveying belt  38  moving circuitously electrostatically attracts the sheet to the surface thereof and conveys the sheet rightward.  
         [0036]     As the photosensitive drum  30  rotates, the charger  50  charges the surface of the photosensitive drum  30  with a uniform positive polarity. Subsequently, the scanning unit  18  irradiates the laser beam L in a high speed scan over the surface of the photosensitive drum  30  to form an electrostatic latent image on the photosensitive drum  30  corresponding to an image that is to be formed on the paper  3 .  
         [0037]     Next, the positively charged toner carried on the surface of the developing roller  26  comes into contact with the photosensitive drum  30  as the developing roller  26  rotates. At this time, the toner is supplied to the electrostatic latent image formed on the surface of the photosensitive drum  30 , that is, the regions on the surface of the positively charged photosensitive drum  30  that were exposed to the laser beam L and, therefore, have a lower potential. The toner supplied to the photosensitive drum  30  develops the electrostatic latent image into a visible image according to a reverse development process so that a toner image is carried on the surface of the photosensitive drum  30 .  
         [0038]     As a sheet of paper  3  conveyed on the conveying belt  38  passes through transfer positions between each of the photosensitive drums  30  and the corresponding transfer roller  39 , the toner image carried on the surface of the photosensitive drum  30  is transferred onto the paper  3  by a transfer bias applied to the transfer roller  39 . After the toner image is transferred onto the paper  3 , the paper  3  is conveyed to a fixing unit  42 .  
         [0039]     The fixing unit  42  is disposed in the main casing  2  to the right of the paper-conveying unit  35 . The fixing unit  42  includes a heating roller  43  and a pressure roller  44  disposed in confrontation with each other for fixing the toner image transferred onto the paper  3  to the surface of the paper  3  with heat. After the toner image has been fixed to the paper  3 , conveying rollers disposed diagonally above and rightward of the fixing unit  42  convey the paper  3  toward discharge rollers  46  disposed in the top section of the main casing  2 . A discharge tray  47  that is substantially level on the left side and slopes downward toward the right side is provided on the top surface of the main casing  2 . After the image-forming process described above is completed for each sheet of paper  3 , the discharge rollers  46  discharge the paper  3  onto the discharge tray  47  where the sheets accumulate in a stack.  
         [0040]     Next, the developing unit  22  having a structure that is a feature in the laser printer  1  of the preferred embodiment will be described.  
         [0041]      FIG. 3A  is a side view and  FIG. 3B  a front view of the developing unit  22  according to the preferred embodiment.  FIG. 4  is a perspective view of the frame  21  in which the developing unit  22  of the preferred embodiment is mounted.  FIG. 5  is a side cross-sectional view showing the general structure of the laser printer  1  according to the preferred embodiment when the developing unit  22  is mounted in the frame  21 .  FIG. 6  illustrates pressing members  70  that push against the developing units  22 .  FIG. 7  illustrates separating members  80  for displacing the developing units  22  in a direction away from the photosensitive drums  30 .  
         [0042]     As shown in  FIG. 3B , the developing unit  22  employed in the laser printer  1  of the preferred embodiment includes the box-shaped case  23 , and the toner-accommodating chamber  24  formed in the top section of the case  23  and filled with toner of the respective color. An elongated opening is formed in the lower side of the case  23 , and the developing roller  26  is disposed in this opening.  
         [0043]     As shown in  FIG. 3A , the case  23  has end faces  23   a  formed at both axial ends of the developing roller  26  (see  FIG. 3B ) within planes that are substantially orthogonal to the axial direction (indicated by DX in  FIG. 3B ) of the developing roller  26 . A pair of protrusions  231  and a pair of protrusions  232  are formed on the upper portions of the end faces  23   a  provided at both sides of the case  23 . As shown in  FIG. 3B , the protrusions  231  protrude outward from the end faces  23   a  in a direction parallel to the axis of the developing roller  26 . The protrusions  232  protrude farther outward than the ends of the protrusions  231 . As shown in  FIG. 3A , the protrusions  231  and protrusions  232  are formed at the corners of the case  23 . As shown in  FIG. 3B , a pair of guiding protrusions  233  are provided on the end faces  23   a  near the front ends thereof and protrude outward in a direction parallel to the axis of the developing roller  26 .  
         [0044]     When the top cover  6  is opened, as shown in  FIG. 2 , the image-forming unit  20  accommodated in the main casing  2  can be pulled upward out of the main casing  2  in the preferred embodiment. As described above, the image-forming unit  20  includes the frame  21  that can be disassembled into four blocks  21   a . As shown in  FIG. 4 , each block  21   a  includes one of the photosensitive drums  30  and chargers  50 , as well as one of the cleaning brushes  33  (see  FIG. 1 ) and the like. Each block  21   a  also includes a pair of mounting plates  21   b  extending upward from each axial end of the photosensitive drum  30 . A guiding groove  21   c  for guiding the developing unit  22  is formed in the inner surface of each mounting plate  21   b  at opposing positions. The guiding grooves  21   c  function to guide the developing unit  22  mounted in the frame  21  until the developing roller  26  is in contact with the photosensitive drum  30 . More specifically, the developing unit  22  is guided by the guiding protrusions  233  formed on the end faces of the developing unit  22  that slide within the guiding grooves  21   c.    
         [0045]     As shown in  FIG. 6 , the laser printer  1  also includes pressing members  70  provided in the main casing  2  for pressing the respective protrusions  231 . The pressing members  70  are coil springs disposed in the main casing  2  at positions above and opposing each of the protrusions  231  of the developing units  22  when the image-forming unit  20  is accommodated in the main casing  2 . The pressing members  70  push the respective developing units  22  so that the developing rollers  26  are pressed against the photosensitive drums  30 .  
         [0046]     As shown in  FIG. 7 , the laser printer  1  of the preferred embodiment also includes separating members  80  for moving the image-forming unit  20  accommodated in the main casing  2  in a direction that separates the developing rollers  26  from the photosensitive drums  30 . The separating member  80  is configured of a separating piece  82  provided on an end of a rotational shaft  81 . The separating piece  82  is mounted on the rotational shaft  81  in an eccentric position to the rotational center of the rotational shaft  81 . The rotational shaft  81  is parallel to the rotational center of the developing roller  26 , and the separating piece  82  is positioned beneath the protrusion  232 . The separating member  80  separates from the protrusion  232  when the edge of the separating piece  82  having the shortest distance to the rotational shaft  81  opposes the protrusion  232 , and pushes up the protrusion  232  against the urging force of the pressing member  70  when the edge of the separating piece  82  having the longest distance from the rotational shaft  81  opposes the protrusion  232 .  
         [0047]     Next, the effects of using the laser printer  1  having the construction described above will be described.  
         [0048]     The cases  23  in the laser printer  1  have a high stiffness with respect to a force applied along the end face  23   a . Further, the protrusions  231  and protrusions  232  are provided on the upper ends of the end faces  23   a  in the laser printer  1  of the preferred embodiment. Therefore, instead of pressing the case  23  as in the conventional laser printers, the laser printer  1  of the preferred embodiment can apply pressing and separating forces via the protrusions  231  and protrusions  232  without directly applying a force to the case  23  for separating the developing roller  26  from the photosensitive drum  30 . Hence, since the pressing force and separating force are not applied to the case  23  at single points, it is unnecessary to increase the stiffness of the case  23 . Moreover, it is unnecessary to increase the thickness of the case  23  since the pressing and separating forces are applied to the case  23  along the end faces  23   a , which are the stiffest portions of the case  23 .  
         [0049]     Further, by forming the protrusions  232  farther outside than the protrusions  231  and at positions offset from the protrusions  231 , opposing forces are not repeatedly applied to the same areas of the case  23 . Therefore, the developing units in the laser printer  1  of the preferred embodiment can be formed without reinforcing the areas at which the protrusions  231  and protrusions  232  are provided, unlike the conventional developing units  
         [0050]     While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims.  
         [0051]     For example, the operating parts corresponding to the protrusions  231  that are operated by the pressing means need not be provided on the end faces  23   a  of the case  23  to achieve the effects described above.  
         [0052]     Specifically, as shown in  FIG. 8 , the protrusions  232  are preferably provided on the outside of the frame  21  on either side of the mounting plates  21   b  protruding outward in a direction parallel to the axis (indicated by DX in  FIG. 8 ) of the developing roller  26 . However, the protrusions  231  should be disposed inside of the protrusions  232  near the end faces  23   a  and along the axis of the protrusions  232 . Here, “near the end faces  23   a ” should suggest that a portion of the protrusions  231  overlaps the surface of the end faces  23   a . This construction can obtain the same effects as the preferred embodiment described above.  
         [0053]     While the laser printer  1  of the preferred embodiment described above has horizontally juxtaposed developing units  22 , the pressing members  70  and separating members  80  of the preferred embodiment may also be provided in a laser printer having vertically juxtaposed developing units  22 . In such a case, the pressing members  70  push the protrusions  231  of the developing units  22  so that the developing rollers  26  are pressed against the photosensitive drums  30 , while the separating members  80  push the protrusions  232  of the developing units  22  in the opposite direction so that the developing rollers  26  separate from the photosensitive drums  30 .  
         [0054]     While the invention has been described in detail with reference to the above embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.