Patent Publication Number: US-7917059-B2

Title: Developing device and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a developing device and an image forming apparatus. In particular, the present invention relates to a developing device for developing toner to a latent static image to form an image and an image forming apparatus used for a copier, a printer, a facsimile, a multi-function printer (MFP), and the likes. 
     A conventional image forming apparatus of an electro-photography type such as a printer, a copier, a facsimile, and a multi-functional printer (MFP) is provided with a developing device of a process cartridge type detachably attached to an apparatus main body, thereby improving a maintenance operation. The developing device is integrally formed of a photosensitive drum, a charge roller for charging the photosensitive drum, a developing roller, and a cleaning device. 
     In recent years, high print quality has been required. Consequently, it is necessary to print an image with high definition and high quality without color shift. To this end, it is necessary to provide each component of an image forming apparatus with high dimension accuracy, high assembly accuracy, and high installation accuracy as well as constant stability. 
     In general, the developing device includes the developing roller for developing toner on the photosensitive drum. The developing roller is situated at a position contacting with or away from the photosensitive drum by a small distance for attaching toner to a static latent image on the photosensitive drum. A drive device rotates the developing roller. The photosensitive drum and the developing roller are supported on a side plate, i.e., a part of a frame of the developing device. 
     (Refer to Patent Reference) 
     
         
         Patent Reference: Japan Patent Publication No. 2006-220875 
       
    
     In the conventional image forming apparatus described above, the frame of the developing device supports both end portions of shafts of the photosensitive drum and the developing roller, and the frame is formed of a plate member. Accordingly, it is difficult to obtain sufficient rigidity against a twisting force applied to the developing device. As a result, when the developing device is assembled, or each roller rotates during a printing operation and causes frictional resistance at a contacting point with respect to an adjacent roller, the developing device may twist and each roller may contact with each other. In this case, a rotational load of the developing device changes, and there is a difference in image quality between left side and right side, thereby increasing the rotational load of the developing device and lowering print quality. 
     In view of the problem described above, an object of the invention is to provide a developing device and an image forming apparatus, in which it is possible to solve the problems of the conventional image forming apparatus. In the developing device and the image forming device, it is possible to minimize a change in a rotational load and prevent image quality from lowering. 
     Further objects of the invention will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     In order to attain the objects described above, according to the present invention, a developing device is detachably attached to an image forming apparatus. The developing device includes a first frame member; a second frame member disposed to face the first frame member; a shaft member for connecting the first frame member and the second frame member; a first engagement member disposed at one end portion of the shaft member for engaging the first frame member; a second engagement member disposed at the other end portion of the shaft member for engaging the second frame member; and a fixing member for fixing at least one of the first engagement member and the second engagement member. 
     In the present invention, it is possible to correct and prevent a twisted state of the developing device. Accordingly, it is possible to minimize a change in a rotational load and prevent image quality from lowering. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view showing a chassis of a developing device according to a first embodiment of the present invention; 
         FIG. 2  is a schematic view showing an image forming apparatus according to the first embodiment of the present invention; 
         FIG. 3  is a sectional view showing the developing device according to the first embodiment of the present invention; 
         FIG. 4  is a backside view showing the chassis of the developing device according to the first embodiment of the present invention; 
         FIG. 5  is a schematic view showing a first end chassis member of the developing device according to the first embodiment of the present invention; 
         FIG. 6  is a schematic view showing a second end chassis member of the developing device according to the first embodiment of the present invention; 
         FIG. 7  is a schematic enlarged view showing the second end chassis member of the developing device according to the first embodiment of the present invention; 
         FIG. 8  is a schematic view showing a first end chassis member of a developing device according to a second embodiment of the present invention; 
         FIG. 9  is a schematic enlarged view No.  1  showing the first end chassis member of the developing device according to the second embodiment of the present invention; 
         FIG. 10  is a schematic enlarged view No.  2  showing the first end chassis member of the developing device according to the second embodiment of the present invention; and 
         FIG. 11  is a schematic sectional view showing the first end chassis member of the developing device according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereunder, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. 
     First Embodiment 
     A first embodiment of the present invention will be explained.  FIG. 2  is a schematic view showing an image forming apparatus  10  according to the first embodiment of the present invention.  FIG. 3  is a sectional view showing a developing device  11  according to the first embodiment of the present invention. 
     In the embodiment, the image forming apparatus  10  may include any type of image forming apparatus such as a printer of an electro-photography type, a facsimile, a copier, a multi-function printer having functions of a printer, a facsimile, and a copier. The image forming apparatus  10  is a tandem type color printer of an electro-photography type. 
     As shown in  FIG. 2 , in the image forming apparatus  10 , developing devices  11   a ,  11   b ,  11   c , and  11   d  corresponding to four colors, i.e., cyan (C), magenta (M), yellow (Y), and black (K), respectively, are arranged sequentially along a transportation path of a medium  16 . The developing devices  11   a ,  11   b ,  11   c , and  11   d  have an identical configuration and retain toner in different colors. 
     In the embodiment, the developing devices  11   a ,  11   b ,  11   c , and  11   d  have exposure heads  14   a ,  14   b ,  14   c , and  14   d  corresponding to the four colors, respectively. In the following description, the developing devices  11   a ,  11   b ,  11   c , and  11   d  and the exposure heads  14   a ,  14   b ,  14   c , and  14   d  may be collectively referred to as the developing device  11  and an exposure head  14 . 
     In the embodiment, the image forming apparatus  10  further includes a medium tray  15  for storing the medium  16  as a recording sheet; a sheet supply roller  17  for separating and supplying the medium  16  one by one from the medium tray  15 ; transportation rollers  18   a  and  18   b  for transporting the medium  16 ; and a transfer belt  19  for transporting the medium  16  and transferring a toner image to the medium  16 . When the transportation rollers  18   a  and  18   b  transport the medium  16  to the transfer belt  19 , static charge is applied to the medium  16  to be attached to the transfer belt  19 . Afterward, while the developing device  11  forms the toner image, the transfer belt  19  transports the medium  16 . 
     In the embodiment, the image forming apparatus  10  includes a fixing unit  20  as a fixing device for fixing the toner image thus transferred to the medium  16  through heat and pressure; discharge rollers  21   a ,  21   b ,  21   c , and  21   d  for discharging the medium  16  with the toner image thus fixed to outside the image forming apparatus  10 ; and a stack cover  23  for holding the medium  16  thus discharged. 
     As shown in  FIG. 3 , the developing device  11  includes a chassis  35  and a toner storage container  30  disposed at an upper portion of the chassis  35  for storing toner  31 . A toner hopper  35   a  is disposed in the chassis  35 , and a supply opening  29  is formed in an upper surface of the toner hopper  35   a . The toner  31  in the toner storage container  30  is supplied to the toner hopper  35   a  through the supply opening  29 , so that the toner  31  is temporarily stored in the toner hopper  35   a.    
     In the embodiment, a photosensitive drum  13  as an image supporting member is rotatably attached to the chassis  35 . The photosensitive drum  13  has a shaft  38  as a shaft member with both end portions attached to the chassis  35  for functioning as a central axis. Further, there are provided around the photosensitive drum  13  a charge roller  41 ; the exposure head  14 ; a developing roller  33 ; a toner supply roller  34 ; a cleaning blade  42 ; and a waste toner discharge member  43 . 
     In the embodiment, the charge roller  41  functions as a charge device for uniformly and evenly charging the photosensitive drum  13  rotating in an arrow direction  13   e . The exposure head  14  includes an LED (Light Emitting Diode) head and the likes for irradiating a surface of the photosensitive drum  13  according to an image signal, so that the surface of the photosensitive drum  13  is selectively exposed to form a static latent image thereon. 
     In the embodiment, the developing roller  33  rotates in an arrow direction  33   a  for attaching the toner  31  to the surface of the photosensitive drum  13  with the static latent image formed thereon, thereby forming the toner image. The toner supply roller  34  rotates in an arrow direction  34   a  for supplying the toner  31  in the toner hopper  35   a  to the developing roller  33 . A stirring member  32  is disposed inside the toner hopper  35   a  for stirring the toner  31 . A developing blade  40  is provided for forming a thin layer of the toner  31  on the developing roller  33 . 
     In the embodiment, the transfer belt  19  transfers the toner image formed on the surface of the photosensitive drum  13  to the medium  16  through a static force. The cleaning blade  42  has an end portion abutting against the surface of the photosensitive drum  13  for removing the toner  31  remaining on the surface of the photosensitive drum  13 . The waste toner discharge member  43  discharges the toner  31  as waste toner removed from the surface of the photosensitive drum  13  with the cleaning blade  42  outside the developing device  11 . 
     A configuration of the chassis  35  of the developing device  11  will be explained next.  FIG. 1  is an exploded view showing the chassis  35  of the developing device  11  according to the first embodiment of the present invention.  FIG. 4  is a backside view showing the chassis  35  of the developing device  11  according to the first embodiment of the present invention.  FIG. 5  is a schematic view showing a first end chassis member  37  of the developing device according  11  to the first embodiment of the present invention.  FIG. 6  is a schematic view showing a second end chassis member  36  of the developing device  11  according to the first embodiment of the present invention.  FIG. 7  is a schematic enlarged view showing the second end chassis member  36  of the developing device  11  according to the first embodiment of the present invention. 
     As shown in  FIG. 4 , the first end chassis member  37  as a first frame member is attached to the chassis  35  with a connection member such as a screw (not shown) for covering one end portion of the chassis  35 . Further, the second end chassis member  36  as a second frame member is attached to the chassis  35  with a connection member such as a screw (not shown) for covering the other end portion of the chassis  35 . 
     In the embodiment, end portions of the shaft  38  are supported on the first end chassis member  37  and the second end chassis member  36 , so that the shaft  38  does not rotate. Note that the photosensitive drum  13  is attached to the shaft  38  to be rotatable around the shaft  38 . The shaft  38  has a first protruding portion  38   b  and a second protruding portion  38   a  protruding outside the first end chassis member  37  and the shaft  38 , respectively. The first end chassis member  37  and the second end chassis member  36  have a first fixing protrusion  37   a  and a second fixing protrusion  36   a  protruding outside from outer side surfaces thereof, respectively. The first fixing protrusion  37   a  and the second fixing protrusion  36   a  function as fixing protrusions for fixing the first end chassis member  37  and the second end chassis member  36  inside the image forming apparatus  10 . 
     As shown in  FIG. 1 , an assembly standard jig  60  is provided for assembling the developing device  11 . The assembly standard jig  60  has insertion grooves  60   a ,  60   b ,  60   c , and  60   d . The second fixing protrusion  36   a , the second protruding portion  38   a , the first fixing protrusion  37   a ; and the first protruding portion  38   b  are inserted into the insertion grooves  60   a ,  60   b ,  60   c , and  60   d , respectively. 
     As shown in  FIG. 5 , a second engagement pin  50  as a second engagement member extends in a direction perpendicular to an axial direction of the shaft  38 . One end portion of the second engagement pin  50  is inserted into the shaft  38  to be fixed, and the other end portion of the second engagement pin  50  is fixed with a second fixing rib  36   c  formed on an inner side surface of the second end chassis member  36 . 
     As shown in  FIG. 6 , a first engagement pin  51  as a first engagement member extends in a direction perpendicular to the axial direction of the shaft  38 . One end portion of the first engagement pin  51  is inserted into the shaft  38  to be fixed, and the other end portion of the first engagement pin  51  is fixed to a fixing member  52 . 
     As shown in  FIGS. 6 and 7 , the fixing member  52  is detachably attached to the first end chassis member  37  with an attachment member  53  such as a screw. In this case, the attachment member  53  is inserted into a guide groove  37   c  with a semi-circular shape penetrating through a sidewall of the first end chassis member  37 . Accordingly, when the attachment member  53  is loosen, the fixing member  52  can move along a circular path around the shaft  38 . When the attachment member  53  is tightened, the fixing member  52  is fixed to the sidewall of the first end chassis member  37 . 
     An operation of the image forming apparatus  10  will be explained next. When the image forming apparatus  10  receives a print command from a host device such as a personal computer (not shown), the image forming apparatus  10  starts an image forming operation. The sheet supply roller  17  separates and supplies the medium  16  stored in the medium tray  15  one by one, and the transportation rollers  18   a  and  18   b  transport the medium  16  to the transfer belt  19 . Then, the developing device  11  corresponding to each color forms the static latent image on the surface of the photosensitive drum  13 . The static latent image is developed to form the toner image, and the toner image is transferred to the medium  16  transported with the transfer belt  19 . 
     In this case, the toner supply roller  34  of the developing device  11  is driven to rotate in the arrow direction  34   a  with a drive source (not shown), so that the toner  31  is supplied to the developing roller  33 . The developing roller  33  is driven to rotate in the arrow direction  33   a  with a drive source (not shown). The developing blade  41  forms and charges a thin layer of the toner  31  on the developing roller  33 . 
     In the embodiment, the photosensitive drum  13  is driven to rotate in the arrow direction  13   e  with a drive source (not shown), and the charge roller  41  uniformly charges the surface of the photosensitive drum  13 . Then, the exposure head  14  selectively exposes the surface of the photosensitive drum  13 , thereby forming the static latent image. A portion thus exposed has a potential of 0 V. The toner  31  on the developing roller  33  is supplied to the static latent image, thereby forming the toner image. 
     Afterward, the toner image formed on the surface of the photosensitive drum  13  is transferred to the medium  16  transported with the transfer belt  19  through a static force. The cleaning blade  42  scrapes off and removes the toner  31  remaining on the surface of the photosensitive drum  13  and not transferred to the medium  16 . The waste toner discharge member  43  discharges the toner  31  thus removed outside the developing device  11  as waste toner. 
     After the toner image is transferred, the medium  16  is transported to the fixing unit  20 , so that the toner image transferred to the medium  16  is fixed to the medium  16  through heat and pressure. After the fixing unit  20  fixes the toner image to the medium  16 , the discharge rollers  21   a ,  21   b ,  21   c , and  21   d  discharge the medium  16  outside the image forming apparatus  10 , so that the medium  16  is placed on the stacker cover  23 . 
     When the developing device  11  is assembled, after the rollers such as the developing roller  33  and the toner supply roller  34  are attached inside the chassis  35 , the first end chassis member  37  and the second end chassis member  36  are attached. Accordingly, depending on part dimension accuracy or assembly accuracy of the first end chassis member  37  or the second end chassis member  36 , the first end chassis member  37  and the second end chassis member  36  may be shifted in arrow directions  37   b  and  36   b  shown in  FIG. 1  around the shaft  38 , so that the first end chassis member  37  and the second end chassis member  36  are positioned in a twisted relationship. 
     In the embodiment, to this end, the assembly standard jig  60  is used, so that the second fixing protrusion  36   a , the second protruding portion  38   a , the first fixing protrusion  37   a ; and the first protruding portion  38   b  are inserted into the insertion grooves  60   a ,  60   b ,  60   c , and  60   d , respectively. As a result, the first end chassis member  37  and the second end chassis member  36  are positioned in a corrected relationship. 
     In this case, as shown in  FIG. 7 , when the attachment member  53  is loosen and moves along the guide groove  37   c , the fixing member  52  moves together with the attachment member  53  and rotates in an arrow direction  52   a  shown in  FIG. 6  around the shaft  38 . Accordingly, the first end chassis member  37  rotates around the shaft  38 , thereby correcting the twisted relationship of the first end chassis member  37  and the second end chassis member  36 . 
     Once the twisted relationship of the first end chassis member  37  and the second end chassis member  36  is corrected, the attachment member  53  is tightened and fixed to the sidewall of the first end chassis member  37 . Note that it is possible to operate the attachment member  53  from outside the first end chassis member  37 . Accordingly, it is possible to easily correct or adjust the twisted relationship of the first end chassis member  37  and the second end chassis member  36 . 
     As described above, in the embodiment, the one end portions of the first engagement pin  51  and the second engagement pin  50  are attached to the shaft  38 . The other end portions of the first engagement pin  51  and the second engagement pin  50  engage the first end chassis member  37  and the second end chassis member  36 . Further, the fixing member  52  is provided for fixing the other end portion of the first engagement pin  51  to the first end chassis member  37 . Accordingly, it is possible to increase rigidity of the developing device  11  against a twisting force. Further, it is possible to prevent the developing device  11  from twisting during the assemble process or the printing operation, and to prevent a contact state of the rollers from changing, thereby preventing print quality from lowering. 
     Further, in the embodiment, the fixing member  52  is able to move with respect to the first end chassis member  37 . Accordingly, after the developing device  11  is assembled, it is possible to correct the twisted state of the developing device  11 . Further, the fixing member  52  is attached to the first end chassis member  37  with the attachment member  53  that is detachable. Accordingly, it is possible to easily disassemble the developing device  11 , thereby maintaining good recycle ability. 
     Second Embodiment 
     A second embodiment of the present invention will be described below. In the description below, elements in the second embodiment similar to those in the first embodiment are designated by same reference numerals, and explanations thereof are omitted. Explanations of operations and effects in the second embodiment similar to those in the first embodiment are omitted. 
       FIG. 8  is a schematic view showing the first end chassis member  37  of the developing device  11  according to the second embodiment of the present invention.  FIG. 9  is a schematic enlarged view No.  1  showing the first end chassis member  37  of the developing device  11  according to the second embodiment of the present invention.  FIG. 10  is a schematic enlarged view No.  2  showing the first end chassis member  37  of the developing device  11  according to the second embodiment of the present invention.  FIG. 11  is a schematic sectional view showing the first end chassis member  37  of the developing device  11  according to the second embodiment of the present invention. 
     In the second embodiment, the fixing member  52 , the guide groove  37   c , and the first engagement pin  51  have configurations different from those in the first embodiment. 
     As shown in  FIG. 8 , the first engagement pin  51  passes through an insertion hole penetrating through the shaft  38  in a radial direction thereof, so that the first engagement pin  51  moves in the radial direction. 
     In the embodiment, the fixing member  52  engages the one end portion of the first engagement pin  51 . Further, the first engagement pin  51  is rotatable with respect to the fixing member  52  around an engagement portion thereof with the fixing member  52 . 
     In the embodiment, the guide groove  37   a  penetrates through the sidewall of the first end chassis member  37 , and have a linear shape. The attachment member  53  is inserted into the guide groove  37   c  for attaching the fixing member  52  to the first end chassis member  37 . Accordingly, the fixing member  52  and the attachment member  53  move linearly along the guide groove  37   c . Similar to the first embodiment, the attachment member  53  may be a screw or a detachable member. Accordingly, when the attachment member  53  is tightened, the fixing member  52  is fixed to the sidewall of the first end chassis member  37 . 
     In the embodiment, the fixing member  52  is provided with a protruding portion  52   b  to be inserted into the guide groove  37   c . The protruding portion  52   b  is arranged to fit in the guide groove  37   c  without a play. Accordingly, the fixing member  52  stably moves along the guide groove  37   c  without wobble. Further, it is possible to firmly fix the fixing member  52  to the first end chassis member  37  when the fixing member  52  is tightened. Other configurations are similar to those in the first embodiment, and explanations thereof are omitted. 
     An operation of the image forming apparatus  10  will be explained next. In the following description, only an operation of assembling the developing device  11  will be explained. 
     Similar to the first embodiment, upon assembling the developing device  11 , when the first end chassis member  37  and the second end chassis member  36  are positioned in the twisted relationship with the shaft  38  at the center thereof, the assembly standard jig  60  is used to correct the twisted relationship of the first end chassis member  37  and the second end chassis member  36 . 
     In this case, as shown in  FIGS. 9 and 10 , when the attachment member  53  is loosen and moves along the guide groove  37   c  in the arrow direction  52   a , the fixing member  52  moves together with the attachment member  53  linearly in the arrow direction  52   a . At this moment, the one end portion of the first engagement pin  51  rotatably engages the fixing member  52 . Accordingly, the first engagement pin  51  rotates around the shaft  38  in the arrow direction  37   b  shown in  FIGS. 9 and 10 . As a result, the first end chassis member  37  rotates around the shaft  38 , thereby correcting the twisted relationship of the first end chassis member  37  and the second end chassis member  36 . 
     Once the twisted relationship of the first end chassis member  37  and the second end chassis member  36  is corrected, the attachment member  53  is tightened and fixed to the sidewall of the first end chassis member  37 . Note that it is possible to operate the attachment member  53  from outside the first end chassis member  37 . Accordingly, it is possible to easily correct or adjust the twisted relationship of the first end chassis member  37  and the second end chassis member  36 . 
     As shown in  FIG. 9 , the fixing member  52  is situated at a position closest to the shaft  38 . In this state, the first engagement pin  51  forms an angle A 1  with respect to the guide groove  37   c  having a linear shape. As shown in  FIG. 10 , the fixing member  52  is situated at a position furthest to the shaft  38 . In this state, the first engagement pin  51  forms an angle A 2  with respect to the guide groove  37   c  having a linear shape. A relationship between the angle A 1  and the angle A 2  is given by the following equation.
 
A1&lt;A2
 
     In the embodiment, when the first end chassis member  37  and the second end chassis member  36  are twisted at a maximum angle AS, the angle A 1  and the angle A 2  have the following relationship with respect to the angle AS.
 
 AS≦A 2 −A 1
 
     Other operations in the second embodiment are similar to those in the first embodiment, and explanations thereof are omitted. 
     As described above, in the second embodiment, the protruding portion  52   b , i.e., a part of the fixing member  52 , is inserted into the guide groove  37   c . Accordingly, in addition to the effect in the first embodiment, it is possible to increase an contact area between the fixing member  52  and the first end chassis member  37 , thereby further increasing rigidity against a twisting force. 
     In the first and second embodiments, the present invention is applied to the developing device  11 , and may be applicable to an apparatus such as a cleaning device, a toner cartridge, a medium transportation device, a transfer device, and a fixing device, in which toner is used. Further, the present invention is applicable to the image forming apparatus  10  used for a copier, an LED printer, a laser beam printer, a facsimile, an MFP, and the likes. 
     The disclosure of Japanese Patent Application No. 2007-041597, filed on Feb. 22, 2007, is incorporated in the application. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.