Patent Publication Number: US-10310443-B1

Title: Image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2018-5350 filed on Jan. 17, 2018, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to image forming apparatuses using an electrophotographic system, such as copiers, printers, facsimile machines, and multifunction peripherals incorporating their functions. More particularly, the present disclosure relates to image forming apparatuses provided with a mechanism for protecting a photosensitive member arranged near an openable-closable member. 
     Conventional image forming apparatuses using an electrophotographic system, such as printers, copiers, and facsimile machines, transfer a toner image to the surface of a sheet while conveying the sheet to a photosensitive drum. Then, the toner image transferred on the surface of the sheet is fixed to the sheet by a fixing portion. The sheet to which the toner image has now been fixed is discharged to outside the image forming apparatus. A sheet conveying passage leading from the photosensitive drum to the fixing portion can be opened for jam (sheet jam) handling by opening the openable-closable member rotatably supported on an image forming apparatus main body. 
     Here, when the openable-closable member is opened, the surface of the photosensitive drum is exposed to outside the image forming apparatus, and the photosensitive drum is exposed to external light. As a result, a photosensitive layer formed on the surface of the photosensitive drum may be degraded. Also, if the exposed photosensitive drum is touched by a hand or an object, the surface of the photosensitive drum may be contaminated or scratched. 
     To avoid that, there is provided a drum cover that moves, in coordination with the openable-closable member, between a position where the drum cover covers the photosensitive drum and a position where the drum cover is retracted from the sheet conveying passage. When the openable-closable member is closed, the drum cover is retracted from the sheet conveying passage, so that a toner image on the surface of the photosensitive drum can be transferred to a sheet. Opening the openable-closable member for jam handling opens the sheet conveying passage as well as causes the drum cover to cover the surface of the photosensitive drum on the side facing away from the image forming apparatus main body to prevent the surface of the photosensitive drum from being exposed to outside the apparatus. 
     There is provided a cooling portion for preventing an image forming unit including the photosensitive drum and a developing device from being exposed to high temperature due to heat from the fixing device. When the drum cover for protecting the surface of the photosensitive drum is retracted, the drum cover is positioned in the air flow generated by the cooling portion. 
     SUMMARY 
     According to one aspect of the present disclosure, an image forming apparatus has an openable-closable member, an image carrier, a cover sheet, and a cover moving mechanism. The openable-closable member is arranged in an open position where it keeps a recording medium conveying passage open and in a closed position where it keeps the recording medium conveying passage closed. A part of the outer circumferential face of the image carrier is exposed to outside when the recording medium conveying passage is open. The cover sheet is flexible and is reciprocatable between a protection position in which the cover sheet covers a recording medium conveying passage side of the image carrier and a retracted position in which the cover sheet is retracted from the recording medium conveying passage. The cover moving mechanism, as the openable-closable member moves to the closed position, moves the cover sheet to the retracted position and, as the openable-closable member moves to the open position, moves the cover sheet to the protection position. Drawing out the cover sheet arranged in the protection position to the recording medium conveying passage side causes the cover sheet to be arranged in a recording medium removal position where the interval between the image carrier and the cover sheet is larger than that in the protection position. 
     This and other objects of the present disclosure, and the specific benefits obtained according to the present disclosure, will become apparent from the description of embodiments which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional side view showing a main part of an image forming apparatus according to one embodiment of the present disclosure; 
         FIG. 2  is a perspective view showing a cover moving mechanism in the image forming apparatus of the embodiment when an access cover is closed; 
         FIG. 3  is a cross-sectional side view showing the cover moving mechanism in the image forming apparatus of the embodiment when the access cover is closed; 
         FIG. 4  is a perspective view showing the cover moving mechanism in the image forming apparatus of the embodiment when the access cover is open; and 
         FIG. 5  is a perspective view showing the cover moving mechanism in the image forming apparatus of the embodiment when the cover sheet is arranged in a sheet removal position. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the accompanying drawings, embodiments of the present disclosure will be described below.  FIG. 1  is a cross-sectional side view showing a main part of an image forming apparatus  1  according to one embodiment of the present disclosure. The image forming apparatus  1  is a monochrome printer, and is provided with a sheet feeding portion  31  arranged at a lower part of an apparatus main body  1 A, a sheet conveying passage  5  for conveying a sheet P upward from the sheet feeding portion  31 , an image forming portion  2  arranged to the right of the sheet conveying passage  5 , a fixing device  4  arranged above the image forming portion  2 , a cover moving mechanism  20  arranged around a photosensitive drum  3  in the image forming portion  2 , and a cooling portion  40  arranged to the right of the cover moving mechanism  20 . The cooling portion  40  cools down an image forming unit, including the photosensitive drum  3 , a developing device  36 , and a cleaning unit  38 , to which the heat radiated from the fixing device  4  is transmitted as well as a sheet P conveyed through the sheet conveying passage  5  via the fixing device  4 . 
     The sheet feeding portion  31  picks up the sheets P stored in a sheet feeding cassette with a pick-up roller  32  one sheet after another and conveys them to the sheet conveying passage  5 . The sheet conveying passage  5  has a conveying roller  33  and a registration roller pair  34 , and conveys the sheet P sent out from the sheet feeding portion  31  toward the image forming portion  2 . 
     The image forming portion  2  forms a predetermined toner image on a sheet P by an electrophotographic method. The image forming portion  2  includes the photosensitive drum  3  which is pivoted so as to be rotatable in the clockwise direction in  FIG. 1 . Around the photosensitive drum  3 , there are arranged a charger  35 , the developing device  36 , a transfer roller  37 , the cleaning unit  38 , and the like along the rotating direction of the photosensitive drum  3 . 
     The charger  35  is provided with a charging wire to which a high voltage is applied, and by corona discharge from the charging wire, the surface of the photosensitive drum  3  is electrostatically charged uniformly. For the photosensitive drum  3 , an amorphous silicon photosensitive member having an amorphous silicon photosensitive layer as a photosensitive layer or an organic photosensitive member (OPC photosensitive member) with an organic photosensitive layer as a photosensitive layer is used. When the photosensitive drum  3  is irradiated with a laser beam from an exposure unit (unillustrated) based on image data transmitted from a host device such as a personal computer, the surface potential of the photosensitive drum  3  is selectively attenuated to form an electrostatic latent image on the surface of the photosensitive drum  3 . 
     Then, the developing device  36  develops the electrostatic latent image on the surface of the photosensitive drum  3  to form a toner image on the surface of the photosensitive drum  3 . The toner image formed on the surface of the photosensitive drum  3  is transferred to a sheet P by the transfer roller  37 . The toner remaining on the surface of the photosensitive drum  3  after the transfer is removed by the cleaning unit  38 . Residual electric charges on the surface of the photosensitive drum  3  are removed by a static eliminator (unillustrated) in preparation for the next image formation. 
     The sheet P to which the toner image has been transferred is conveyed to the fixing device  4  arranged on the downstream side of the sheet conveying passage  5 . In the fixing device  4 , as the sheet P passes through the nip portion (fixing nip portion) between a fixing roller  4   a  and a pressing roller  4   b , it is heated and pressed and thereby the toner image is fixed to the sheet P. The sheet P on which the toner image is fixed is discharged onto a discharge tray  39  by a discharge roller pair  7 . The sheet conveying passage  5  leading from the sheet feeding portion  31  to the discharge roller pair  7  is in a left part of the apparatus main body  1 A and extends substantially in the up-down direction. 
     On the left wall of the apparatus main body  1 A, an access cover  6  (openable-closable member) is provided. The access cover  6  can be opened and closed with respect to the apparatus main body  1 A for jam handling in the sheet conveying passage  5 . When the access cover  6  is opened, a conveying face that forms the sheet conveying passage  5  is split between the apparatus main body  1 A side and the access cover  6  side, and thus the sheet P left in the sheet conveying passage  5  can be removed. 
     A lower end part of the access cover  6  is rotatably pivoted on the apparatus main body  1 A. By being operated to swing about a pivot, the access cover  6  can be switched between an open state (the state indicated by a dash-dot-line in  FIG. 1 ) in which an opening is formed between the apparatus main body  1 A and the access cover  6  and a closed state (the state indicated by a solid-line in  FIG. 1 ) in which the inside of the apparatus main body  1 A is sealed from outside. When the access cover  6  is in the closed state, it is possible to perform image formation; when the access cover  6  is in the open state, a cover sheet  27  moves from above the photosensitive drum  3  to the left by the action of the cover moving mechanism  20 , which will be described later. With this, when the access cover  6  is opened for jam handling, it is possible to prevent the surface of the photosensitive drum  3  from being scratched through contact with an operator&#39;s hand or a tool, and to prevent the photosensitive layer from degrading due to external disturbance light striking the photosensitive drum  3 . 
       FIG. 2  is a perspective view showing the cover moving mechanism  20  when the access cover  6  is in the closed state (during image formation).  FIG. 3  is a cross-sectional side view showing the cover moving mechanism  20  when the access cover  6  is in the closed state. With reference to  FIGS. 2 and 3 , the cover moving mechanism  20  that moves the cover sheet  27  will be described in detail. 
     As shown in  FIG. 2 , the cover moving mechanism  20  is provided with a link arm  11 , an arm rail  21 , a holder rail  22 , a sheet guide  23  (see  FIG. 3 ), and the cover sheet  27 , as well as a first sheet holder  28  and a second sheet holder  29  which support the cover sheet  27 . 
     The cover sheet  27  is a flexible sheet material formed of high molecular weight polyethylene, and its obverse side (the side opposite to the photosensitive drum  3 ) is coated with a heat reflective film to have heat insulating properties. The length of the cover sheet  27  in the width direction (in the axial direction of the photosensitive drum  3 ) is set to be equal to or longer than the length of the photosensitive drum  3  in the axial direction. The length of the cover sheet  27  in the moving direction (in the left-right direction in  FIG. 2  and in the up-down direction in  FIG. 3 ) is set to be approximately twice as large as the outer diameter of the photosensitive drum  3 . When the access cover  6  (see  FIG. 1 ) is in the closed position, the cover sheet  27  is arranged above the photosensitive drum  3 . The cover sheet  27  has an opaque light shielding portion  27   a  located on the first sheet holder  28  side and a transparent or translucent light transmitting portion  27   b  (the hatched part in  FIG. 2 ) located on the second sheet holder  29  side. 
     The first sheet holder  28  fixedly supports the front edge portion  27   c  of the cover sheet  27  generally over its full width. The second sheet holder  29  fixedly supports the rear edge portion  27   d  of the cover sheet  27  generally over its full width. At the opposite ends of the first sheet holder  28  in the longitudinal direction, there is formed a pair of first engaging bosses  28   a . At the opposite ends of the second sheet holder  29  in the longitudinal direction, there is formed a pair of second engaging bosses  29   a.    
     In the apparatus main body  1 A, a pair of arm rails  21  and a pair of holder rails  22  are fixedly arranged in the width direction. On the arm rail  21 , there is formed a vertical rail groove  21   a  that extends substantially in the up-down direction. On the holder rail  22 , there is formed a horizontal rail groove  22   a  that extends substantially in the horizontal direction. 
     The first engaging bosses  28   a  formed at the opposite ends of the first sheet holder  28  are swingably coupled to a swing shaft  11   a  formed in an upper end part of a pair of link arms  11 . The swing shaft  11   a  is slidably engaged with the vertical rail groove  21   a  formed on the arm rail  21 . In a lower end part of the vertical rail groove  21   a , there is formed a guide groove  21   b  that leads to the vertical rail groove  21   a . The swing shaft  11   a  can be attached to and detached from the vertical rail groove  21   a  via the guide groove  21   b.    
     The link arm  11  is swingably supported, by a swing pivot  11   b  formed at its lower end part, on the access cover  6 . The first sheet holder  28  is movable in coordination with the access cover  6  via the link arm  11 . 
     The second engaging bosses  29   a  formed at the opposite ends of the second sheet holder  29  slidably engage with the horizontal rail grooves  22   a  formed in the pair of holder rails  22 . 
     A sheet guide  23  is arranged between the pair of holder rails  22 . The sheet guide  23  extends in a horizontal direction along the horizontal rail groove  22   a  so as to face the bottom face of the cover sheet  27  and, at the left end (on the arm rail  21  side) of the sheet guide  23 , an arc-shaped curved portion  23   a  is formed. When the first sheet holder  28  moves in the up-down direction and the second sheet holder  29  moves in the horizontal direction, the cover sheet  27  supported by the first sheet holder  28  and the second sheet holder  29  is guided to the curved portion  23   a  of the sheet guide  23  and moves along an arc-shaped orbit around the photosensitive drum  3 . 
       FIG. 4  is a perspective view showing the cover moving mechanism  20  when the access cover  6  is in the open state. With reference to  FIGS. 2, 3, and 4 , operation by the cover moving mechanism  20  for moving the cover sheet  27  will be described in detail. 
     When the access cover  6  is in the closed state, as shown in  FIGS. 2 and 3 , the cover sheet  27  is arranged in a position (hereinafter, called a retracted position) retracted from the sheet conveying passage  5  to above the photosensitive drum  3  and under the fixing device  4  (see  FIG. 1 ). The length of the cover sheet  27  in the movement direction (the left-right direction in  FIG. 3 ) is larger than the length from an upper end part of the vertical rail groove  21   a  (the position of the first sheet holder  28  in the retracted position) to a right end part of the horizontal rail groove  22   a  (the position of the second sheet holder  29  in the retracted position), and thus the cover sheet  27  is in a bent state in the retracted position. The sheet guide  23  is under the cover sheet  27 , and thus, as shown in  FIG. 3 , the cover sheet  27  is bent upward. 
     When the access cover  6  is pivoted in the opening direction as indicated by a dash-dot-dot-line arrow in  FIG. 3  from the state where the access cover  6  is closed, the link arm  11  moves in coordination with the access cover  6 , and the swing shaft  11   a  moves from the upper end part of the vertical rail groove  21   a  in the direction indicated by a solid-line arrow in  FIG. 3 . Accordingly, also the first sheet holder  28  coupled to the swing shaft  11   a  of the link arm  11  moves downward along the vertical rail groove  21   a.    
     As the first sheet holder  28  moves, via the cover sheet  27 , also the second sheet holder  29  moves from the right end part of the horizontal rail groove  22   a  to the left side in the direction indicated by the sold line arrow in  FIG. 3 . With this, the cover sheet  27  is guided along the sheet guide  23  while straightening from the bent state and, in the curved portion  23   a , moves in an arc shape around the photosensitive drum  3 . Then, when the access cover  6  moves to an open position, as shown in  FIG. 4 , the second sheet holder  29  moves to around the middle of the horizontal rail groove  22   a  in the longitudinal direction, and the cover sheet  27  moves from the retracted position as shown in  FIG. 3  to such a position (hereinafter, called a protection position) as to cover the sheet conveying passage  5  side (the left, near side in  FIG. 4 ) and the fixing device  4  side (the upper side in  FIG. 4 ) of the photosensitive drum  3 . 
     In the protection position, the light shielding portion  27   a  of the cover sheet  27  is positioned at the sheet conveying passage  5  side of the photosensitive drum  3 , so that, by shielding the external disturbance light toward the photosensitive drum  3  when the access cover  6  is open, the light shielding portion  27   a  prevents degradation of the photosensitive layer of the photosensitive drum  3 ; it also prevents the surface of the photosensitive drum  3  from being scratched through contact with an operator&#39;s hand or a tool. 
     When the access cover  6  in the open state is pivoted in the closing direction as indicated by a dash-dot-line arrow in  FIG. 3 , the link arm  11  moves in coordination with the access cover  6 , and the swing shaft  11   a  moves upward from the lower end part of the vertical rail groove  21   a . Accordingly, the first sheet holder  28  coupled with the swing shaft  11   a  of the link arm  11  also moves upward along the vertical rail groove  21   a . Also, as the first sheet holder  28  moves upward, a force in the compressing direction acts on the cover sheet  27  between the first sheet holder  28  and the second sheet holder  29 . 
     As a result, with a restoring force (elastic force) of the cover sheet  27 , the second sheet holder  29  is pressed to move to the right in  FIG. 4  along the horizontal rail groove  22   a . Then, the cover sheet  27  is, until the second sheet holder  29  reaches the right end part of the horizontal rail groove  22   a , guided in a straightened state along the sheet guide  23  and, in the curved portion  23   a , the cover sheet  27  moves in an arc shape around the photosensitive drum  3 . 
     After the second sheet holder  29  reaches the right end part of the horizontal rail groove  22   a  and stops, the link arm  11  continues to pivot and the swing shaft  11   a  moves toward the upper end part of the vertical rail groove  21   a . As a result, the distance between the first sheet holder  28  and the second sheet holder  29  becomes smaller than the length of the cover sheet  27  in the moving direction, and thus the cover sheet  27  bends from the straightened state, while moving to above the photosensitive drum  3  to return to the retracted position as shown in  FIGS. 2 and 3 . 
     Here, when the access cover  6  is moved into the open position to remove a jammed sheet P in the sheet conveying passage  5 , if the sheet P is left in front of the cover sheet  27 , the sheet P can be easily removed; however, if the sheet P is left between the cover sheet  27  and the photosensitive drum  3 , it is difficult to recognize the sheet P visually due to the cover sheet  27  and the sheet P may be forgotten to be removed. To avoid this, in this embodiment, the cover sheet  27  can be moved to a position (hereinafter, called a sheet removal position) where the cover sheet  27  is drawn further out to the access cover  6  side from the protection position shown in  FIG. 4 . 
       FIG. 5  is a perspective view showing a state where the cover sheet  27  is moved to the sheet removal position from the state in  FIG. 4 . With reference to  FIGS. 2 to 4 and 5 , operation by the cover moving mechanism  20  for moving the cover sheet  27  to the sheet removal position will be described. 
     When a sheet P has been jammed between the cover sheet  27  and the photosensitive drum  3 , from a state in  FIG. 4  where the cover sheet  27  is arranged in the protection position, the swing shaft  11   a  of the link arm  11  is removed from the vertical rail groove  21   a  via the guide groove  21   b . Then, the link arm  11  is pivoted about the swing pivot  11   b  as the center in the counter-clockwise direction in  FIG. 4 . 
     With this, the first sheet holder  28  coupled with the swing shaft  11   a  in an upper end part of the link arm  11  pivots together with the link arm  11  to move to the left, near side in  FIG. 4 . As a result, the cover sheet  27  is, together with the first sheet holder  28 , drawn out to the sheet conveying passage  5  side (the left, near side in  FIG. 4 ) to be arranged in the sheet removal position shown in  FIG. 5 . In the sheet removal position, the interval between the cover sheet  27  and the photosensitive drum  3  is larger than that in the protection position. 
     According to this embodiment, the cover sheet  27  can be arranged in one of the three positions, namely, the retracted position, the protection position, and the sheet removal position. If a sheet P is jammed between the cover sheet  27  and the photosensitive drum  3 , the cover sheet  27  is arranged in the sheet removal position where the interval between the cover sheet  27  and the photosensitive drum  3  is large. This permits easy removal of a sheet P left between the cover sheet  27  and the photosensitive drum  3 , and brings improved jam handling workability. 
     Also, the light transmitting portion  27   b  of the cover sheet  27  arranged above the photosensitive drum  3  in the protection position is drawn out to the sheet conveying passage  5  side of the photosensitive drum  3 . With this, the presence or the absence of a sheet P left between the cover sheet  27  and the photosensitive drum  3  can be recognized visually through the light transmitting portion  27   b , and a failure to remove a sheet P can be prevented. 
     When jam handling is finished, the swing shaft  11   a  of the link arm  11  is engaged with the vertical rail groove  21   a  via the guide groove  21   b . Then, when the link arm  11  is pivoted about the swing pivot  11   b  as the center in the clockwise direction in  FIG. 5 , the cover sheet  27  is arranged back in the protection position shown in  FIG. 4 . 
     In the sheet removal position where the light transmitting portion  27   b  is drawn out to the sheet conveying passage  5  side of the photosensitive drum  3 , the photosensitive drum  3  is irradiated with external disturbance light via the light transmitting portion  27   b . However, after jam handling is finished, if the cover sheet  27  is promptly returned to the protection position according to the procedure described above, the time for which the photosensitive drum  3  is irradiated with external disturbance light can be minimized, and thus there is no risk that the photosensitive layer of the photosensitive drum  3  is degraded. 
     The embodiment described above is in no way meant to limit the present disclosure, which thus allows for many modifications and variations within the spirit of the present disclosure. For example, in the above embodiment, when the cover sheet  27  is moved from the protection position to the retracted position, with the restoring force (elastic force) of the cover sheet  27 , the second sheet holder  29  is pressed to move to the right in  FIG. 4  along the horizontal rail groove  22   a . Instead of this structure, it is also possible to fit a biasing member such as a coil spring to the second sheet holder  29  on the side opposite to the cover sheet  27  so that the second sheet holder  29  moves to the right in  FIG. 4  by the biasing force of the biasing member. 
     The present disclosure is applicable not only to monochrome printers like the one shown in  FIG. 1  but also to various types of image forming apparatuses provided with a drum cover for protecting the photosensitive drum, such as color printers, monochrome and color copiers, and facsimile machines. 
     The present disclosure is applicable to image forming apparatuses using an electrophotographic system such as copiers, printers, facsimile machines, and multifunction peripherals incorporating their functions. Based on the present disclosure, it is possible to provide an image forming apparatus which prevents degradation of and damage to an image carrier by means of a cover for protecting the image carrier and which offers improved jam handling operability.