Patent Publication Number: US-8538289-B2

Title: Developing device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2010-250783 filed Nov. 9, 2010. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a developing device and an image forming apparatus. 
     (ii) Related Art 
     There are known developing devices each including a developing roller that opposes an image carrier on which an electrostatic latent image is formed and that transports developer while rotating to develop the electrostatic latent image. 
     SUMMARY 
     According to an aspect of the present invention, there is provided a developing device including a cylindrical developer transport body that opposes an image carrier on which an electrostatic latent image is formed and that transports developer while rotating to develop the electrostatic latent image, a housing that holds the developer transport body and that defines an exposed portion exposed outside on a side of the developer transport body close to the image carrier and an unexposed portion, the housing including, on a side of the unexposed portion, a storage portion that stores the developer such that the developer is in contact with the developer transport body, and a layer-thickness regulation member that defines the storage portion and regulates a layer thickness of the developer transported to the exposed portion by rotation of the developer transport body, the layer-thickness regulation member including one side extending in a rotation axis direction of the developer transport body and provided close to a surface of the developer transport body at a boundary where the surface of the developer transport body shifts from the unexposed portion to the exposed portion during rotation, a first portion extending from the side in a direction intersecting the surface, and a second portion extending from the first portion toward the unexposed portion. The housing includes first faces that face from both ends in the rotation axis direction of the developer transport body toward the center in the rotation axis direction on the side of the unexposed portion and that define both ends of the storage portion in the rotation axis direction, a second face that faces the first portion of the layer-thickness regulation member on the side of the unexposed portion and on an outer side of the storage portion, and a third face that faces the second portion of the layer-thickness regulation member on the side of the unexposed portion and on the outer side of the storage portion. The developing device further includes a closing member that closes a gap between the layer-thickness regulation member and the second face and the third face of the housing, and a magnet that opposes a boundary between the first portion and the second portion of the layer-thickness regulation member and is provided between the second face and the third face of the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic structural view of an exemplary embodiment of the present invention; 
         FIG. 2  is a perspective view of an end of a developing unit; 
         FIG. 3  is a perspective view of the end illustrated in  FIG. 2 , as viewed at an angle different from that of  FIG. 2 ; and 
         FIG. 4  is a cross-sectional view of the end of the developing unit, taken along line IV-IV of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of the present invention will be described below with reference to the drawings. 
       FIG. 1  is a schematic structural view of an image forming apparatus  1  according to an exemplary embodiment of the present invention. In the image forming apparatus  1  illustrated in  FIG. 1 , a developing device of the exemplary embodiment is incorporated. 
     The image forming apparatus  1  includes a document reading section  10 , an image forming section  20 , and a sheet storage section  30 . 
     The document reading section  10  includes a document feeding table  11  on which documents S are stacked. The documents S stacked on the document feeding table  11  are fed out one by one, and are transported in a transport path  13  by transport rollers  12 . Characters and images recorded on each transported document S are read by a document reading optical system  15  provided below a document reading plate  14  formed of transparent glass, and the document S is then output onto a document output table  16 . 
     The document reading section  10  also includes a hinge extending in the right-left direction on the rear side thereof. On the hinge, the document feeding table  11  and the document output table  16  are turned up together. Below the turned document feeding table  11  and document output table  16 , the document reading plate  14  is provided. In the document reading section  10 , a document may be placed upside down on the document reading plate  14 , instead of being placed on the document feeding table  11 . In this case, the document reading optical system  15  moves in the direction of arrow A so as to read characters and images from the document placed on the document reading plate  14 . 
     Image signals obtained by the document reading optical system  15  are input to a processing and control circuit  21 . The processing and control circuit  21  controls the operations of the parts of the image forming apparatus  1  so as to form an image based on the input image signals. 
     The sheet storage section  30  provided in the lower part of the image forming apparatus  1  includes three sheet supply containers  31 _ 1 ,  31 _ 2 , and  31 _ 3 , for example, in which sheets P having different sizes are stacked. The sheet supply containers  31 _ 1 ,  31 _ 2 , and  31 _ 3  are drawn when sheets P are supplied therein. 
     For example, from a sheet supply container that stores sheets P having a size corresponding to the size of the document (e.g., the sheet supply container  31 _ 3 ), of these sheet supply containers  31 _ 1 ,  31 _ 2 , and  31 _ 3 , the sheets P are fed out by a pickup roller  32 , and are separated one by one by loosening rollers  33 . Each one separated sheet P is transported upward by transport rollers  34  in the direction of arrow B, and is further transported after the timing of transportation downstream of standby rollers  35  is adjusted by the standby rollers  35 . The transportation downstream of the standby rollers  35  will be described below. 
     The image forming section  20  includes a manual feed tray  22  that is turned open and close on a lower end thereof. The image forming section  20  also has a function of feeding a sheet placed on the opened manual feed tray  22  in the direction of arrow C. 
     A photoconductor  51  that rotates in the direction of arrow D is provided in the center of the image forming section  20 . Around the photoconductor  51 , a charging unit  52 , an exposure unit  53 , a developing device  60 , a charge eliminating unit  54 , and a cleaner  55  are arranged. Also, a transfer unit  56  is provided around the photoconductor  51  with a below-described intermediate transfer belt  71  being disposed therebetween. 
     The photoconductor  51  is roll-shaped. Charges are held on a surface of the photoconductor  51  by charging and are eliminated by exposure, so that an electrostatic latent image is formed on the surface. This photoconductor  51  corresponds to an example of an image carrier in the invention. 
     The charging unit  52  charges the surface of the photoconductor  51  at a certain charging potential. 
     The exposure unit  53  receives image signals from the processing and control circuit  21 , and outputs exposure light modulated according to the input image signals. After being charged by the charging unit  52 , the photoconductor  51  is irradiated with the exposure light from the exposure unit  53 , and an electrostatic latent image is formed on the surface of the photoconductor  51 . The electrostatic latent image formed on the surface of the photoconductor  51  by irradiation with the exposure light is then developed by the developing device  60 , thereby forming a toner image on the surface of the photoconductor  51 . The developing device  60  includes six developing units  61 ,  62 ,  63 ,  64 ,  65 , and  66 . The developing device  60  is a so-called rotary developing device that rotates in the direction of arrow E so as to move any one of the six developing units  61  to  66  (the developing unit  61  in a state of  FIG. 1 ) to a position opposing the photoconductor  51 . The electrostatic latent image formed on the photoconductor  51  is developed by the developing unit opposing the photoconductor  51  (developing unit  61  in this case) to form a toner image. The developing device  60  corresponds to an example of a developing device of the invention. Each of the six developing units  61 ,  62 ,  63 ,  64 ,  65 , and  66  corresponds to an example of a developing unit of the present invention. 
     The six developing units  61  to  66  provided in the developing device  60  store toners of yellow (Y), magenta (M), cyan (C), black (K) and two other specific colors corresponding to the user applications. Examples of specific colors corresponding to the user applications are transparent toner used for image glazing and toner adjusted to a color frequently used by the user. To develop the electrostatic latent image on the photoconductor  51 , the developing unit that stores the color toner to be currently used is rotated to the position opposing the photoconductor  51 , and develops the electrostatic latent image with the color toner stored in the developing unit. 
     The toner images formed on the photoconductor  51  by development with the developing units are transferred onto the intermediate transfer belt  71  by the action of the transfer unit  56 . 
     After transfer, the charges on the photoconductor  51  are eliminated by the charge eliminating unit  54 , and residual toner on the photoconductor  51  are then removed by the cleaner  55 . 
     The intermediate transfer belt  71  is an endless belt stretched around plural rollers  72 , and circulates in the direction of arrow F. A transfer unit  73  is located near the intermediate transfer belt  71  with a sheet transport path R being disposed therebetween. Downstream of the transfer unit  73  in the circulating direction of the intermediate transfer belt  71 , a cleaner  74  is provided to remove toner remaining on the intermediate transfer belt  71  after transfer with the transfer unit  73 . The transfer unit  73  and the cleaner  74  are movable into contact with and away from the intermediate transfer belt  71 . When forming a multicolor image, the transfer unit  73  and the cleaner  74  are separated from the intermediate transfer belt  71 . In this state, a process of forming a toner image of one certain color on the photoconductor  51  and transferring the toner image onto the intermediate transfer belt  71  is repeated for the plural developing units (plural color toners) while rotating the developing device  60 , whereby plural toner images of plural colors are sequentially transferred and superimposed on the intermediate transfer belt  71  to form a multicolor image. 
     After that, the transfer unit  73  is brought into contact with the intermediate transfer belt  71 , and a sheet P is fed from the standby rollers  35  so that the sheet P reaches a transfer position, where the transfer unit  73  is located, at a time when the multicolor toner image reaches the transfer position. At the transfer position, the multicolor toner image is transferred from the intermediate transfer belt  71  onto the sheet P by the action of the transfer unit  73 . Here, a combination of the transfer unit  56 , the intermediate transfer belt  71 , and the transfer unit  73  corresponds to an example of a transfer unit of the present invention. The sheet P on which the toner image is transferred is further transported in the direction of arrow G, and is heated and pressurized by a fixing unit  80 , so that a fixed toner image is formed on the sheet P. The fixing unit  80  corresponds to an example of a fixing unit of the present invention. The sheet P passing through the fixing unit  80  is further transported by transport rollers  34  in the direction of arrow H, and is output onto a sheet output tray  23 . 
     The cleaner  74  also moves into contact with the intermediate transfer belt  71 , and removes toner remaining on the intermediate transfer belt  71  after transfer with the transfer unit  73 . 
     The image forming apparatus  1  may form images on both surfaces of a sheet P. To form images on both surfaces of the sheet P, a sheet P having an image only on a first surface, as described above, is transported by transport rollers  37  in the direction of arrow I by switching a guide member  36 , instead of being output to the sheet output tray  23 . After that, the transport direction of the sheet P is reversed by the reverse rotation of the transport rollers  37 , and the sheet P is transported in the direction of arrow J. Then, the sheet P is guided by another guide member  38  and is transported by transport rollers  39  in the direction of arrow K. 
     After that, an image is formed on a second surface of the sheet P, in a manner similar to the above. The sheet P having the images on both surfaces is then output onto the sheet output tray  23 . 
     Next, a detailed description will be given of the six developing units  61 ,  62 ,  63 ,  64 ,  65 , and  66  provided in the image forming apparatus  1  illustrated in  FIG. 1 . Since the developing units  61 ,  62 ,  63 ,  64 ,  65 , and  66  have similar structures, the developing unit  61  opposing the photoconductor  51  in the state of  FIG. 1  will be described on behalf of these developing units. 
       FIG. 2  is a perspective view of an end of the developing unit  61 .  FIG. 3  is a perspective view of the end of  FIG. 1 , as viewed at an angle different from that of  FIG. 2 .  FIG. 4  is a cross-sectional view of the end of the developing unit  61 , taken along line IV-IV of  FIG. 2 . 
     As illustrated in  FIGS. 2 to 4 , the developing unit  61  includes a housing  611 , a developing roller  612 , a layer-thickness regulation blade  613 , a magnet roller  614  (see  FIG. 4 ), magnet rubbers  615 , magnetic plates  616 , side seals  6101 , and magnets  6102 . 
     The perspective view of  FIG. 2  illustrates the developing unit  61 , as viewed through the layer-thickness regulation blade  613  and the side seal  6101 . Further, the perspective view of  FIG. 3  illustrates the developing unit  61  through the layer-thickness regulation blade  613 . 
     The developing roller  612  is a cylindrical roller that opposes the photoconductor  51  (see  FIG. 1 ) on which an electrostatic latent image is formed and that develops the electrostatic latent image on the photoconductor  51  by transporting developer while rotating in the direction of arrow D. The developing roller  612  corresponds to an example of a developer transport body of the present invention. 
     The housing  611  is molded from resin and holds the developing roller  612 . The housing  611  defines an exposed portion  612   a  exposed outside on a photoconductor  51  side of the developing roller  612 , and an unexposed portion  612   b . The housing  611  includes, on the unexposed portion  612   b  side of the developing roller  612 , a storage portion  611   a  that stores developer such that the developer is in contact with the developing roller  612 . The housing  611  also includes a wall  611   b  (see  FIG. 4 ) having a sectional shape shown by a broken line in  FIG. 4  and extending in the rotation axis direction of the developing roller  612 . The storage portion  611   a  is defined by the wall  611   b , and is provided between the wall  611   b  and the developing roller  612 . The developer in the storage portion  611   a  is agitated by three augers  617   a ,  617   b , and  617   c  (see  FIG. 4 ) while being transported back and forth in the rotation axis direction of the developing roller  612 . This transportation reduces variations in amount of developer in the rotation axis direction. Further, both ends of the housing  611  on the developing roller  612  side in the rotation axis direction of the developing roller  612  include first faces  611   c , second faces  611   d , third faces  611   e , and fourth faces  611   f . The first faces  611   c  face from both ends toward the center in the rotation axis direction so as to define both ends of the storage portion  611   a  in the rotation axis direction. The second faces  611   d  extend in a direction intersecting the surface of the developing roller  612  and face toward the exposed portion  612   a  at a boundary where the surface of the developing roller  612  shifts from the unexposed portion  612   b  to the exposed portion  612   a  during rotation in the direction of arrow D. The third faces  611   e  extend from the second faces  611   d  toward the unexposed portion  612   b  and face toward a side opposite the developing roller  612 . The fourth faces  611   f  are curved in an arc shape along the surface of the unexposed portion  612   b  of the developing roller  612 . Recesses  611   g  are provided at positions where the first faces  611   c , the second faces  611   d , and the third faces  611   e  meet, and the magnets  6102  are embedded in the recesses  611   g . The housing  611  corresponds to an example of a housing of the present invention. The exposed portion  612   a  corresponds to an example of an exposed portion of the present invention, the unexposed portion  612   b  corresponds to an example of an unexposed portion of the invention, and the storage portion  611   a  corresponds to an example of a storage portion of the invention. The first faces  611   c  correspond to examples of first faces of the invention, the second faces  611   d  correspond to an example of a second face of the invention, and the third faces  611   e  correspond to an example of a third face of the invention. 
     The layer-thickness regulation blade  613  is a metallic member that defines the storage portion  611   a  with the housing  611  and that regulates the thickness of a layer of developer transported on the exposed portion  612   a  by the rotation of the developing roller  612 . The layer-thickness regulation blade  613  corresponds to an example of a layer-thickness regulation member of the present invention. The layer-thickness regulation blade  613  is detachably fixed to the second faces  611   d  with screws  6131  so that unwanted substances, such as paper dust and aggregated toner, caught between the layer-thickness regulation blade  613  and the developing roller  612  are removed. When the layer-thickness regulation blade  613  is detachably fixed to the second faces  611   d  with the screws  6131 , for example, the image forming apparatus  1  may be easily disassembled for resource recovery at the time of disposal. The layer-thickness regulation blade  613  includes one side  613   a  that extends in the rotation axis direction of the developing roller  612  and that is located close to the surface of the developing roller  612  at a boundary where the surface of the developing roller  612  shifts from the unexposed portion  612   b  to the exposed portion  612   a  during rotation in the direction of arrow D. The layer-thickness regulation blade  613  regulates the thickness of a layer of developer transported from a gap between the developing roller  612  and the layer-thickness regulation blade  613  toward the exposed portion  612   a . Further, the layer-thickness regulation blade  613  includes a first portion  613   b  (see  FIG. 4 ) shaped like a flat plate extending from the side  613   a  in a direction intersecting the surface of the developing roller  612 , and a second portion  613   c  (see  FIG. 4 ) shaped like a flat plate extending from the first portion  613   b  toward the unexposed portion  612   b . The first portion  613   b  and the second portion  613   c  of the layer-thickness regulation blade  613  are joined by welding such that the layer-thickness regulation blade  613  has an L-shaped cross section, as illustrated in  FIG. 4 . Since the layer-thickness regulation blade  613  is fixed to the second faces  611   d  with the screws  6131 , as described above, the second faces  611   d  face the first portion  613   b  on the unexposed portion  612   b  side and on the outer side of the storage portion  611   a , and the third faces  611   e  face the second portion  613   c  on the unexposed portion  612   b  side and on the outer side of the storage portion  611   a . The first portion  613   b  of the layer-thickness regulation blade  613  defines a front part of the storage portion  611   a  in the direction of arrow D. That is, the first portion  613   b  defines the storage portion  611   a  on the forward side in the direction of transportation of developer to the exposed portion  612   a  with the rotation of the developing roller  612 . Further, the second portion  613   c  of the layer-thickness regulation blade  613  defines an upper part of the storage portion  611   a  in  FIG. 4 . In the layer-thickness regulation blade  613 , the gap between the side  613   a  and the surface of the developing roller  612  is set within the range of 0.5 to 0.8 mm such that a developer layer of a desired thickness is formed on the developing roller  612 . The side  613   a  of the layer-thickness regulation blade  613  corresponds to an example of one side of the invention, the first portion  613   b  corresponds to an example of a first portion of the invention, and the second portion  613   c  corresponds to an example of a second portion of the invention. 
     The magnet roller  614  in the developing roller  612  illustrated in  FIG. 4  is a magnet including magnetic poles extending in the rotation axis direction. That is, a first magnetic pole  614   a  is a north pole pointing toward the storage portion  611   a . The first magnetic pole  614   a  serves to attract the developer in the storage portion  611   a  onto the developing roller  612 . A second magnetic pole  614   b  is a south pole located downstream of the first magnetic pole  614   a  and upstream of the exposed portion  612   a  in the rotating direction of the developing roller  612 . The second magnetic pole  614   b  serves to apply transport force to the developer passing through the gap between the developing roller  612  and the layer-thickness regulation blade  613 . A third magnetic pole  614   c  is a north pole, and serves to transport the developer held on the developing roller  612  after the thickness of the developer layer is regulated. A fourth magnetic pole  614   d  is a south pole opposing the photoconductor  51  (see  FIG. 1 ). The fourth magnetic pole  614   d  serves to attract carriers in the developer, which develops the electrostatic latent image on the photoconductor  51 , onto the developing roller  612 . A fifth magnetic pole  614   e  is the same north pole as the first magnetic pole  614   a , and serves to separate the developer from the developing roller  612 . 
     The magnet rubbers  615  are plate-shaped flexible magnets. The magnet rubbers  615  are held by the fourth faces  611   f  of the housing  611  that are curved in an arc shape along the surface of the unexposed portion  612   b  of the developing roller  612  at both ends of the developing roller  612  in the rotation axis reaction. The magnet rubbers  615  are curved in an arc shape in the rotating direction of the developing roller  612  along the surface of the developing roller  612  and are located at a distance from the developing roller  612 . The magnet rubbers  615  form naps of developer, and close the gaps between the magnet rubbers  615  and the magnet roller  614  by the naps of developer, that is, the magnet rubbers  615  serve to prevent the developer from leaking from the gaps in the rotation axis direction. 
     The magnetic plates  616  are held on the first faces  611   c  of the housing  611 . The first faces  611   c  face from both ends toward the center in the rotation axis direction, and define both ends of the storage portion  611   a  in the rotation axis direction. The magnetic plates  616  have sides  616   a  extending in the rotating direction of the developing roller  612  and located close to the developing roller  612  at boundaries between both ends of the developing roller  612  (portions provided close to the fourth faces  611   f  so as to hold the magnet rubbers  615 ) and a center portion of the developing roller  612  (a portion that faces the storage portion  611   a  such as to be in contact with the developer in the storage portion  611   a  and that defines the storage portion  611   a ). Naps of developer are formed between the sides  616   a  of the magnetic plates  616  and the developing roller  612 . The magnetic plates  616  also prevent, by the naps of developer, the developer from leaking through gaps between the developing roller  612  and the sides  616   a  and gaps between the developing roller  612  and the fourth faces  611   f  holding the magnet rubbers  615 . 
     As described above with reference to  FIG. 1 , the developing device  60  of the exemplary embodiment is a rotary developing device that rotates in the direction of arrow E (see  FIG. 1 ). For this reason, the developer in the storage portion  611   a  moves in the storage portion  611   a  with the rotation of the developing device  60 . Since the developer moves in the storage portion  611   a  in this way, it is expected that the developer will be sufficiently prevented from leaking in the rotation axis direction through between the layer-thickness regulation blade  613  and the second faces  611   d  and the third faces  611   e  of the housing  611 . 
     In the exemplary embodiment, the side seals  6101  are provided to prevent leakage of the developer from between the layer-thickness regulation blade  613  and the second faces  611   d  and the third faces  611   e  of the housing  611 . The side seals  6101  are clamped in the gaps between the layer-thickness regulation blade  613  and the second faces  611   d  and the third faces  611   e  of the housing  611  so as to close the gaps. The side seals  6101  are formed of a material having an elasticity higher than that of the housing  611 , for example, urethane. Further, the side seals  6101  are stuck on the second faces  611   d  and the third faces  611   e  of the housing  611 . The side seals  6101  serve to prevent the developer from leaking in the rotation axis direction from between the layer-thickness regulation blade  613  and the second faces  611   d  and the third faces  611   e  of the housing  611 . The side seals  6101  correspond to an example of a closing member of the present invention. 
     As described above, the layer-thickness regulation blade  613  is detachably fixed to the second faces  611   d  with the screws  6131 . Further, the layer-thickness regulation blade  613  is a member of L-shaped cross section that is formed by bonding the flat first portion  613   b  and the flat second portion  613   c  by welding. For this reason, small gaps X (see  FIG. 4 ) are easily formed between a boundary between the first portion  613   b  and the second portion  613   c  of the layer-thickness regulation blade  613  and portions of the side seals  6101  opposing the boundary. It is also expected to prevent leakage of the developer from the small gaps X. Although this leakage prevention is also expected when the developing device is not a rotary developing device, unlike the exemplary embodiment, it is emphasized more when the rotary developing device is adopted. 
     In the exemplary embodiment, the magnets  6102  are provided to prevent leakage of the developer from the small gaps X. As described above, the recesses  611   g  are provided at the positions where the first faces  611   c , the second faces  611   d , and the third faces  611   e  meet. The magnets  6102  oppose the boundary between the first portion  613   b  and the second portion  613   c  of the layer-thickness regulation blade  613 , and are embedded in the recesses  611   g . That is, the magnets  6102  are provided at positions between the second faces  611   d  and the third faces  611   e  and shifted toward the storage portion  611   a . The magnets  6102  form naps of developer to close the small gaps X, and prevent the developer from leaking in the rotation axis direction from the small gaps X. The magnets  6102  correspond to an example of a magnet opposing a boundary between the first portion and the second portion of the layer-thickness regulation member and provided between the second face and the third face of the housing. 
     In addition, the developing unit  61  also includes a seal roller  618  (see  FIG. 4 ) and a metallic plate  619  (see  FIG. 4 ) provided below the developing roller  612 . The metallic plate  619  extends in contact with the seal roller  618 . The seal roller  618  and the metallic plate  619  prevent dropping of the developer held on the surface of the developing roller  612  and transported from the exposed portion  612   a  to the unexposed portion  612   b.    
     In the above-described embodiment, the magnets of the present invention oppose the boundary between the first portion  613   b  and the second portion  613   c  of the layer-thickness regulation blade  613  and are provided at the positions where the first faces  611   c , the second faces  611   d , and the third faces  611   e  of the housing  611  meet. The magnets of the invention are not limited thereto, and for example, may be provided at positions opposing the boundary between the first portion  613   b  and the second portion  613   c  of the layer-thickness regulation blade  613  and apart from the storage portion  611   a  between the second faces  611   d  and the third faces  611   e  of the housing  611 . 
     While the rotary developing device is given as an example of the developing device of the invention, the developing device of the invention is not limited thereto. For example, the developing device may perform development with only one developing unit that does not move from a position opposing the image carrier. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.