Patent Publication Number: US-2023161290-A1

Title: Image forming apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an image forming apparatus including a guide member which guides a sheet from a photosensitive drum to a transfer nip area. 
     BACKGROUND 
     In an electrophotographic type image forming apparatus, a developing nip area is formed between a developing roller of a developing device and a photosensitive drum, and a transferring nip area is formed between a transferring roller and the photosensitive drum. An electrostatic latent image formed on the photosensitive drum is developed into a toner image at the developing nip area, and the developed toner image is transferred from the photosensitive drum to a sheet at the transferring nip area. The sheet is conveyed along a predetermined conveying direction and guided to the transferring nip area by a guide member. On the conveying path on the upstream side of the transferring nip area in the sheet conveying direction or in the vicinity of the conveying path, a developer (a toner) scattered from the developing device tends to accumulate. 
     Therefore, in order to prevent the toner from entering between the developing device and the guide member, a gap between the guide member and the developing device may be blocked by a blocking member such as a sponge. 
     On the other hand, in the image forming apparatus, a process unit in which the developing device and the photosensitive drum are unitized may be detachably supported by the apparatus main body. The process unit is detached from the apparatus main body by being turned upward around a rotation axis along the horizontal direction and then pulled out along a direction orthogonal to the rotation axis. The above-described blocking member also serves to prevent the toner accumulated on the upper surface of the guide member from falling when the process unit is turned. 
     In a case where the blocking member is provided, when the leading end of the sheet guided along the guide member comes into contact with the photosensitive drum, a closed space is formed by the developing device, the blocking member, the guide member, the sheet, and the photosensitive drum. When the sheet moves in accordance with the rotation of the photosensitive drum, the volume of the space changes by the amount of the movement of the sheet, and an air flow is generated in the space, and the position of the toner image formed on the photosensitive drum is shifted, resulting in the generation of image defects, such as transverse stripes. 
     Therefore, the guide member described in Patent document 1 is provided with a rib at the tip end portion, and a gap through the rib is formed between the conveyed sheet and the tip end portion. As a result, the change in the volume of the space can be reduced when the sheet moves in accordance with the rotation of the photosensitive drum. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         Japanese Unexamined Patent Application Publication No. 2017-198818 
       
    
     OUTLINE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the guide member described in the above-described patent document, since a gap is opened between the guide member and the sheet, there is a case where an air flow flowing through the gap to the conveying path is generated. Then, there is a problem that the scattered toner flows into the conveying path by the air flow. In such a situation where the problem that occurs when the blocking member is provided is not sufficiently solved, it is preferable not to provide the blocking member so as not to form the above-described closed space. However, in the case where the blocking member is not provided, there is a problem that the toner accumulated on the upper surface of the guide member falls when the process unit is turned. 
     In view of the above circumstances, it is an object of the present invention to provide an image forming apparatus capable of suppressing the generation of air flow when the sheet enters the transferring nip area and preventing the toner from falling when the process unit is turned. 
     Means of Solving the Problems 
     In order to solve the above problems, an image forming apparatus according to the present invention includes a process unit which is configured to be turned upward around a turning shaft and then detached from an apparatus main body, wherein the process unit includes: a photosensitive drum rotating in a predetermined rotating direction; a developing device which faces a surface of the photosensitive drum to form a developing nip area; a guide member which comes into contact with an upper surface of a sheet and guides the sheet to a downstream side of the developing nip area in the rotating direction; and a seal member supported between the developing device and the guide member in a turnable manner, wherein the seal member opens a gap between the developing device and the guide member in a state where the process unit is attached to the apparatus main body, and when the process unit is turned upward when detached from the apparatus body, the seal member is turned to close the gap between the developing device and the guide member. 
     Effects of the Invention 
     According to the present invention, since the seal member is turned to a posture for opening the gap between the guide member and the developing device and a posture for blocking the toner accumulated on the guide member, with the turning of the process unit, it becomes possible to suppress the air flow generated when the sheet is conveyed to the transferring nip area and to prevent the toner accumulated on the guide member from falling. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a side view schematically showing an inner structure of an image forming apparatus according to one embodiment of the present invention. 
         FIG.  2    is a perspective view showing a seal member of the image forming apparatus according to the embodiment of the present invention. 
         FIG.  3    is a side view showing the seal member when a process unit is attached, in the image forming apparatus according to the embodiment of the present invention. 
         FIG.  4    is a perspective view showing an end portion of the seal member attached to a developing device, in the image forming apparatus according to the embodiment of the present invention. 
         FIG.  5 A  is a side view schematically showing a state in which an upper cover is opened, in the image forming apparatus according to the embodiment of the present invention. 
         FIG.  5 B  is a side view schematically showing a state in which a front cover is opened and the process unit is turned, in the image forming apparatus according to the embodiment of the present invention. 
         FIG.  5 C  is a side view schematically showing a state in which the process unit is pulled out of an apparatus main body, in the image forming apparatus according to the embodiment of the present invention. 
         FIG.  6    is a side view showing the seal member when the process unit is turned, in the image forming apparatus according to the embodiment of the present invention. 
         FIG.  7    is a side view explaining a state in which a sheet comes into contact with a photosensitive drum as a comparative example. 
     
    
    
     EMBODIMENT FOR CARRYING OUT THE INVENTION 
     Hereinafter, with reference to the attached drawings, an image forming apparatus according to the present invention will be described. 
     First, with reference to  FIG.  1   , the entire structure of the image forming apparatus will be described.  FIG.  1    is a side view schematically showing the inner structure of the image forming apparatus. Hereinafter, the left side of the paper on which  FIG.  1    is drawn is referred to as the front side of the image forming apparatus. Reference numerals Fr, Rr, L, and R in each drawing indicate the front, rear, left, and right sides of the image forming apparatus. 
     The image forming apparatus  1  includes an apparatus main body  3  having an approximately rectangular parallelepiped hollow part. On the top plate of the apparatus main body  3 , a vertical rear wall  5  and a discharge tray  7  inclined upwardly from the lower end of the rear wall  5  are formed. An opening is formed on the top plate in front of the discharge tray  7 . The opening is opened and closed by an upper cover  9 . When the opening is opened by the upper cover  9 , the hollow part of the apparatus main body  3  is exposed through the opening. A sheet discharge port  11  is formed on the upper portion of the rear wall  5 . 
     In the lower portion of the front plate of the apparatus main body  3 , a manual sheet feeding port  13  is formed. Further, a manual sheet feeding tray  15  is supported on the front plate of the apparatus main body  3  in a rotatable manner around a fulcrum below the manual sheet feeding port  13 . An opening is formed in the front plate above the manual sheet feeding port  13 . The opening is opened and closed by a front cover  17 . When the opening is opened by the front cover  17 , the hollow part of the apparatus main body  3  is exposed through the opening. 
     In the hollow part of the apparatus main body  3 , a sheet feeding cassette  21 , a sheet feeding part  23 , an image forming part  25 , and a fixing device  27  are housed. Further, a main conveying path  29 , an inversion path  31 , and a manual sheet feeding path  33  along which the sheet is conveyed are formed in the apparatus main body  3 . 
     The sheet feeding cassette  21  is housed in the lower portion of the hollow part, and is detachable along the front-and-rear direction through the opening formed in the front plate of the apparatus main body  3 . The sheet feeding cassette  21  includes a placement plate  37  on which the sheet S is placed, and a retard roller  39 . The placement plate  37  is supported on the bottom plate of the sheet feeding cassette  21  so as to be turnable upward and downward around the rear end portion. The retard roller  39  is disposed in front of the placement plate  37 . 
     The sheet feeding part  23  is disposed above the front end portion of the sheet feeding cassette  21 , and includes a pickup roller  41  and a feed roller  43  arranged in front of the pickup roller  41 . The pickup roller  41  is rotated in contact with the sheet S placed on the placement plate  37  turned upward, and sends the sheet S forward. The feed roller  43  comes into contact with the retard roller  39  to form a separation nip area between them. 
     The image forming part  25  is disposed above the sheet feeding cassette  21 , and includes a photosensitive drum  47 , a charger  49 , a developing device  51 , a transferring roller  53 , a cleaning device  55 , and an exposure device  57 . The photosensitive drum  47  is supported so as to be rotatable in the counterclockwise direction of  FIG.  1   . The charger  49 , the developing device  51 , the transferring roller  53 , and the cleaning device  55  are arranged in order along the rotating direction of the photosensitive drum  47  around the photosensitive drum  47 . In this example, the charger  49  is disposed above the photosensitive drum  47 , the developing device  51  is disposed on the front side pf the photosensitive drum  47 , the transferring roller  53  is disposed below the photosensitive drum  47 , and the cleaning device  55  is disposed on the rear side of the photosensitive drum  47 . 
     The developing device  51  includes a developing housing  61 , two agitating members  63 , and a developing roller  65 . The two agitating members  63  are housed in the developing housing  61  to agitate the developer. The developing roller  65  is arranged to face the photosensitive drum  47  through the opening of the developing housing  61 , and forms a developing nip area between the developing roller  65  and the photosensitive drum  47 . At the developing nip area, the toner moves from the developing roller  65  to the photosensitive drum  47 . A toner container  67  is detachably connected to the developing housing  61 . 
     The transferring roller  53  faces the photosensitive drum  47  from below and forms a transferring nip area between the photosensitive drum  47  and the transferring roller  53 . 
     The fixing device  27  is disposed on the rear side of the image forming part  25 , and includes a fixing roller and a pressing roller. 
     The main conveying path  29  is formed so as to curve upward from the separation nip area, extend rearward substantially horizontally through the transferring nip area and the fixing device  27 , and curve upward from the fixing device  27  toward the discharge port  11 . A direction along the main conveying path  29  is defined as a conveying direction of the sheet S, and the upstream side and the downstream side in the following description indicate the upstream side and the downstream side in the conveying direction of the sheet S. The inversion path  31  branches from the main conveying path  29  on the downstream side of the fixing device  27 , and merges with the main conveying path  29  on the downstream side of the separation nip area. The manual sheet feeding path  33  merges with the main conveying path  29  on the downstream side of the separation nip area from the manual sheet feeding port  13 . 
     On the main conveying path  29 , an intermediate rollers pair  71 , a registration rollers pair  73 , a switchback path  75 , and a discharge rollers pair  77  are provided in order from the upstream side. The intermediate rollers pair  71  is disposed on the downstream side of the junction of the inversion path  31 , the manual sheet feeding path  33  and the main conveying path  29 . The registration rollers pair  73  is disposed between the intermediate rollers pair  71  and the transferring nip area. The switchback path  75  is disposed on the downstream side of the fixing device  27 . The discharge rollers pair  77  is disposed inside the discharge port  11 . 
     The main conveying path  29  from the registration rollers pair  73  to the transferring nip area is formed between an upper guide member  81  and a lower guide member  83  below the developing device  51  along a substantially horizontal direction from the front side to the rear side. The upper guide member  81  is supported by the developing housing  61  of the developing device  51 , and the lower guide member  83  is supported by the apparatus main body  3 . 
     The upper guide member  81  has a width corresponding to the maximum size of the sheet and a predetermined length along the conveying direction. The lower surface of the upper guide member  81  is formed to be planner and is curved in an upward arc shape along the conveying direction. 
     The photosensitive drum  47 , the charger  49 , the developing device  51 , the cleaning device  55 , the toner container  67  and the upper guide member  81  are unitized as a process unit P. As described above, the charger  49  is disposed above the photosensitive drum  47 , the developing device  51  and the upper guide member  81  are disposed in front of the photosensitive drum  47 , and the cleaning device  55  is disposed on the rear side of the photosensitive drum  47 . The process unit P has an end portion on the side of the cleaning device  55 . The process unit P is positioned at a predetermined position with respect to the apparatus main body  3 , and the end portion of the process unit P is turnably supported by a turning shaft  87  extending along the horizontal direction. That is, when the process unit P is attached at the predetermined position, the photosensitive drum  47  faces the transferring roller  53  to form the transferring nip area, and the upper guide member  81  faces the lower guide member  83  to form the main conveying path. Attachment/detachment of the process unit P will be described later. 
     A seal member  91  is provided in a gap G between the developing device  51  and the upper guide member  81 . The seal member  91  will be described with reference to  FIG.  2    to  FIG.  4   .  FIG.  2    is a perspective view showing the seal member,  FIG.  3    is a side view showing the seal member attached to the developing device, and  FIG.  4    is a perspective view showing the end portion of the seal member attached to the developing device. 
     As shown in  FIG.  2   , the seal member  91  includes a shaft member  93 , a sheet body  95  supported by the shaft member  93  in a cantilever manner, weights  99  provided at the left and right ends of the shaft member  93 , and bosses  97  protruding from the outer surfaces of the weights  99 . 
     The shaft member  93  is an elongated member having a rectangular cross section, and has a length longer than the maximum width of the sheet S. A plurality of fixing pieces  93   a  having the same thickness as that of the shaft member  93  protrude from the rear surface of the shaft member  93  at predetermined intervals in the left-and-right direction. The sheet body  95  has a rectangular shape long in the left-and-right direction, and is made of flexible material. The front end portion of the sheet body  95  is fixed to the lower surfaces of the shaft member  93  and the fixing pieces  93   a  by adhesion or the like. 
     Each of the two weights  99  has a rectangular parallelepiped shape long in the upper-and-lower direction, and is made of material such as resin. The right and left end surfaces of the shaft member  93  are fixed to the upper portion of the inner surfaces of the weights  99 , and the weights  99  extend downward from the shaft member  93 . The boss  97  protrudes from the upper portion of the outer surface of each weight  99 . 
     As shown in  FIG.  3   , the seal member  91  is disposed as close as possible to the photosensitive drum  47  with a posture in which the sheet body  95  extends forward on the opposite side to the photosensitive drum  47 . Both bosses  97  (see  FIG.  2   ) are rotatably supported by shaft supporting portions  61   a  (see  FIG.  4   ) formed on the lower surface of the developing housing  61 . The left and right weights  99  are accommodated in notches  81   a  (see  FIG.  4   ) formed in the upper guide member  81 . 
     The seal member  91  is supported by the weights  99  such that the sheet body  95  is kept in a substantially horizontal posture. Specifically, the weight of the weights  99  is set such that the sheet body  95  is kept in a substantially horizontal posture where a force in which the fixing piece  93   a  and the sheet body  95  rotate the shaft member  93  in the counterclockwise direction of  FIG.  3    is balanced by the force in which the weights  99  rotates the shaft member  93  in the clockwise direction of  FIG.  3   . The posture of the seal member  91  is referred to as an equilibrium posture. 
     In such a state that the seal member  91  is supported in the equilibrium posture, the tip end portion of the sheet body  95  is separated upward from the upper guide member  81 . That is, when the process unit P is attached to the apparatus main body  3 , a gap G is formed between the developing housing  61  of the developing device  51  and the upper guide member  81 . 
     Next, an image forming operation will be described. First, the charger  49  charges the photosensitive drum  47 , and the exposure device  57  exposes the photosensitive drum  47  based on image data. Thus, an electrostatic latent image is carried on the photosensitive drum  47 . The developing device  51  develops the electrostatic latent image into a toner image. On the other hand, the sheet S placed on the placement plate  37  of the sheet feeding cassette  21  is fed by the pickup roller  41 , and after being separated at the separation nip area, is conveyed to the main conveying path  29 . Thereafter, the sheet S is conveyed by the intermediate rollers pair  71 , and after the conveying timing is adjusted by the registration rollers pair  73 , the sheet S is conveyed to the transferring nip area. 
     The upper surface of the sheet S passed through the registration rollers pair  73  is conveyed along the lower surface of the upper guide member  81 , and guided from the upper guide member  81  to the photosensitive drum  47  along the curved direction of the lower surface of the upper guide member  81 . At this time, the leading end of the sheet S comes into contact with the surface of the photosensitive drum  47  from the upstream side in the rotating direction of the photosensitive drum  47 , and enters the transferring nip area as the photosensitive drum  47  rotates. 
     At the transferring nip area, the toner image carried on the photosensitive drum  47  is transferred to the sheet S. Thereafter, the sheet S is conveyed to the fixing device  27 . The fixing device  27  fixes the toner image to the sheet. The sheet on which the toner image is fixed is conveyed along the main conveying path  29  toward the discharge port  11 , discharged through the discharge port  11  by the discharge rollers pair  77 , and stacked on the discharge tray  7 . The toner remaining on the photosensitive drum  47  after the toner image is transferred to the sheet is removed by the cleaning device  55 . 
     Next, one example of the process unit P detaching method will be described with reference to  FIG.  5 A  to  FIG.  5 C  and  FIG.  6   .  FIG.  5 A  to  FIG.  5 C  are side views schematically explaining the image forming apparatus in which the process unit is turned.  FIG.  6    is a side view showing the seal member when the process unit is turned. 
     When the process unit P is detached from the apparatus main body  3 , as shown in  FIG.  5 A , the upper cover  9  is turned to open the hollow part of the apparatus main body  3 . Then, the toner container  67  (see  FIG.  1   ) is detached from the developing device  51  and pulled out through the opening of the top plate of the apparatus main body  3 . Next, as shown in  FIG.  6 B , the front cover  17  is turned to open the hollow part, and the process unit P is turned upward around the turning shaft  87 . The turning angle is 11 degrees, for example. 
     With the turning of the process unit P, as shown in  FIG.  6   , the seal member  91  is turned by its own weight in the counterclockwise direction of  FIG.  6    with respect to the developing device  51 , and the tip end of the sheet body  95  comes into contact with the upper guide member  81 . At this time, the tip end of the sheet body  95  is slightly deformed along the upper surface of the upper guide member  81 , and the seal member  91  is slightly turned in the counterclockwise direction in  FIG.  6    from the equilibrium posture. When the process unit P is turned, the weights  99  does not come into contact with the upper guide member  81 . 
     Thereafter, as shown in  FIG.  5 C , the process unit P is pulled out obliquely along the front and upper direction through the openings of the top plate and the front plate of the apparatus main body  3 . Thus, the process unit P is detached from the apparatus main body  3 . 
     With reference to  FIG.  7   , as a comparative example, a case will be described, in which a blocking member  101  for blocking the gap G between the developing device  51  and the upper guide member  81  is provided. In this case, when the leading end of the sheet S comes into contact with the surface of the photosensitive drum  47 , a closed space X surrounded by the developing device  51  (the developing housing  61  and the developing roller  65 ), the blocking member  101 , the upper guide member  81 , the sheet S and the photosensitive drum  47  is formed. When the leading end of the sheet S moves toward the transferring nip area as the photosensitive drum  47  is rotated, the volume of the space X changes (increases) by the amount of the movement Y. When the volume of the space X changes as described above, a downwardly air flow is generated in the space X, and the position of the toner image carried on the surface of the photosensitive drum  47  is shifted downward, resulting in image defects such as transverse stripes. 
     On the other hand, in the present embodiment, as described above, the gap G is opened between the developing device  51  and the upper guide member  81 , and the closed space as in the comparative example is not formed. Therefore, since the generation of air flow can be suppressed when the tip end of the sheet S moves toward the transferring nip area as the photosensitive drum  47  is rotated, so that no image defect is generated. 
     However, if the gap G is thus provided, the toner scattered through the gap G may be accumulated on the upper guide member  81 . Then, if the process unit P is turned upward when the process unit P is detached from the apparatus main body  3 , the toner T accumulated on the upper guide member  81  may fall through the gap G between the upper guide member  81  and the developing device  51 . 
     However, in the present embodiment, if the process unit P is turned when the process unit P is detached from the apparatus main body  3 , as shown in  FIG.  6   , the tip end of the sheet body  95  of the seal member  91  comes into contact with the upper guide member  81 , so that the toner T accumulated on the upper guide member  81  is blocked by the sheet body  95 . Therefore, the toner accumulated on the upper guide member  81  can be prevented from falling. 
     Further, since the seal member  91  is rotated by its own weight to a posture of opening the gap between the upper guide member  81  and the developing device  51  and a posture of bringing the sheet body  95  into contact with the upper guide member  81  as the process unit P is turned, the configuration of rotating the seal member  91  becomes unnecessary. 
     Although the present invention has been described in connection with certain embodiments, the present invention is not limited to the above embodiments. Those skilled in the art will be able to modify the above embodiments without departing from the scope and spirit of the invention.