Patent Publication Number: US-9851675-B2

Title: Image forming apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an image forming apparatus. 
     BACKGROUND ART 
     Conventionally, image forming apparatuses, such as copiers, printers, and facsimiles, include a feeding device for feeding a sheet to an image forming unit. The feeding device includes a supporting member configured to support at least one sheet thereon, and a feeding roller configured to feed the sheet supported by the supporting member. 
     PTL 1 describes a configuration where a supporting member is moved up and down by a cam mounted on the same shaft as a feeding roller. In the configuration described in PTL 1, the supporting member can be lowered by the cam after completion of a print job. This allows the user to easily place additional sheets. 
     PTL 2 describes a configuration where a developing roller is brought into contact with a photosensitive drum when image formation is performed, whereas the developing roller is separated from the photosensitive drum when image formation is not performed. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1 Japanese Patent Laid-Open No. 4-350033 
         PTL 2 Japanese Patent Laid-Open No. 2011-018017 
       
    
     If a configuration for switching the positional relation between the supporting member and the feeding member and a configuration for switching the positional relation between the developing member and the photosensitive member are independently provided in the image forming apparatus, the resulting configuration of the apparatus is complex and undesirable. 
     An object of the present invention is to provide an image forming apparatus capable of switching, with a simple configuration, the positional relation between the supporting member and the feeding member and the positional relation between the developing member and the photosensitive member. 
     SUMMARY OF INVENTION 
     The present invention provides an image forming apparatus including a supporting member configured to support at least one sheet thereon; a feeding number configured to feed the sheet; a photosensitive member; a developing member configured to develop a latent image formed on the photosensitive member; driving means for generating a driving force; and switching means for switching, by the driving force, a positional relation between the supporting member and the feeding member and a positional relation between the photosensitive member and the developing member, between a first state and a second state where the supporting member and the feeding member are more distant from each other than in the first state and the photosensitive member and the developing member are more distant from each other than in the first state. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating a configuration of an image forming apparatus according to a first embodiment. 
         FIG. 2  is a perspective view illustrating a configuration of the image forming apparatus according to the first embodiment. 
         FIGS. 3A to 3D  are cross-sectional views illustrating an operation of the image forming apparatus according to the first embodiment. 
         FIG. 4  is a diagram showing a sequence in the image forming apparatus according to the first embodiment. 
         FIG. 5  is a cross-sectional view illustrating a configuration of an image forming apparatus according to a second embodiment. 
         FIGS. 6A to 6D  are cross-sectional views illustrating an operation of the image forming apparatus according to the second embodiment. 
         FIG. 7  is a diagram showing a sequence in the image forming apparatus according to the second embodiment. 
         FIG. 8  is a cross-sectional view illustrating a configuration of a conventional image forming apparatus. 
         FIG. 9  is a sequence diagram of the conventional image forming apparatus. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     An image forming apparatus of a first embodiment to which the present invention is applied will now be specifically described.  FIG. 1  is a cross-sectional view illustrating a general configuration of an image forming apparatus  30 .  FIG. 2  is a perspective view of the image forming apparatus  30 . 
     As illustrated in  FIG. 1 , the image forming apparatus  30  includes a feeding tray  2  that holds a stack of sheets  1 . When a print job signal is input from a host computer (not shown) connected to the image forming apparatus  30 , a feeding roller (feeding member)  3  in the image forming apparatus  30  rotates to feed the top sheet  1  held in the feeding tray  2 . The fed sheet  1  is guided by a conveying guide  4  and conveyed to a registration roller pair  5 . In synchronization with image information formed on a photosensitive drum (photosensitive member)  8  in a process cartridge  7 , the sheet  1  conveyed by the registration roller pair  5  is further conveyed by a scanner unit  6  to a nip portion (transfer portion) between the photosensitive drum  8  and a transfer roller  9 . 
     A toner image on the photosensitive drum  8  is developed by the process cartridge  7  and a developing cartridge  103 . A developing roller (developing member)  103   b  in the developing cartridge  103  rotates while being in contact with the photosensitive drum (photosensitive member)  8 , thereby developing a latent image formed on the photosensitive drum  8 . A transfer process is performed by a transfer bias applied to the transfer roller  9 . The toner image formed on the surface of the photosensitive drum  8  is thus directly transferred to the sheet  1  at the transfer portion. The sheet  1  having the toner image transferred thereto is conveyed to a fixing device  10 , where the toner image is fixed onto the sheet  1  by heat and pressure. The sheet  1  having the toner image fixed thereto is discharged by a discharge roller pair  11  to the outside of the image forming apparatus and then onto a discharge tray  12 . 
     As illustrated in  FIG. 1 , a CPU of the image forming apparatus  30  is connected to a driving means including a motor (driving source) M that generates a driving force, a first clutch including a first solenoid that controls transmission of the driving force of the motor M, and a second clutch including a second solenoid. The first solenoid is disposed in a drive transmission path between the motor M and a feeding shaft  108  (described below), and the second solenoid is disposed in a drive transmission path between the motor M and a separation cam shaft  107  (described below). 
     The feeding shaft  108  is rotatably disposed in a frame member (apparatus main body)  105  of the image forming apparatus  30 . When a driving signal is input from the CPU to the first solenoid, the feeding shaft  108  rotates a full turn in a clockwise (CW) direction in  FIG. 1 . The feeding roller  3  is securely supported on the axis of the feeding shaft  108 . The feeding roller  3  feeds the top sheet  1  on a lifting plate (supporting member)  13  by rotating while being in contact with the top sheet  1 . 
     The lifting plate  13  that supports the sheet  1  is disposed in the frame member  105  to be pivotable about a pivot center  13   a . As illustrated in  FIG. 2 , the lifting plate  13  has a lifting plate rib (first engaged portion)  13   b . In the first embodiment, the lifting plate rib  13   b  is molded as an integral part of the lifting plate  13 . The lifting plate rib  13   b  can be engaged with a slider boss (first engaging portion)  101   a  (described below). By a lifting plate spring  14  serving as a first elastic member, the lifting plate  13  is elastically biased toward the feeding roller  3  (upward in  FIG. 1 ) such that the sheet  1  supported by the lifting plate  13  comes into contact with the feeding roller  3 . The lifting plate spring  14  used here is a compression spring. 
     The developing cartridge  103  is disposed to be pivotable about a pivot center  103   a  with respect to the process cartridge  7 . A cartridge spring  110  serving as a second elastic member is disposed between the process cartridge  7  and the developing cartridge  103 . The cartridge spring  110  biases the developing roller  103   b  toward the photosensitive drum  8 . The cartridge spring  110  is a compression spring. By the cartridge spring  110 , the developing cartridge  103  is elastically biased about the pivot center  103   a  in the CW direction. 
     The developing cartridge  103  has an engagement boss (second engaged portion)  103   c . In the first embodiment, the engagement boss  103   c  is molded as an integral part of the developing cartridge  103 . The engagement boss  103   c  is provided such that it can be engaged with an engagement claw (second engaging portion)  102  (described below). 
     A cartridge guide  104  is securely supported by the frame member  105 . The process cartridge  7  is provided such that it can be attached to and detached from the image forming apparatus  30  through the cartridge guide  104 . The cartridge guide  104  is configured to guide the attachment and detachment of the process cartridge  7 . 
     The first embodiment includes a rotatable separation cam (first moving member)  100  for switching the positional relation between the lifting plate  13  and the feeding roller  3  and the positional relation between the photosensitive drum  8  and the developing roller  103   b . The separation cam  100  can take a first cam position (first rotational position) illustrated in  FIG. 3A  (described below), and a second cam position (second rotational position) illustrated in  FIG. 3C  (described below). 
     The separation cam  100  is securely supported on the axis of a separation cam shaft  107 . The separation cam shaft  107  is disposed to be rotatable with respect to the frame member  105 . When a driving signal is input from the CPU to the second solenoid, the separation cam shaft  107  rotates a half turn in the CW direction in  FIG. 1 . 
     The first embodiment includes a slider (second moving member)  101  that moves in accordance with the rotation of the separation cam  100 . The slider  101  is disposed to be movable between a first travel position illustrated in  FIG. 3A  (described below) and a second travel position illustrated in  FIG. 3C  (described below). The slider  101  can slide in the right and left (horizontal) direction in  FIG. 1  by being guided by a slider guide  106 . The slider guide  106  is securely supported by the frame member  105 . As illustrated in  FIG. 2 , the slider  101  has the engagement claw  102  and the slider boss  101   a . In the first embodiment, the slider boss  101   a  is molded as an integral part of the slider  101 . 
     As illustrated in  FIG. 2 , the slider boss  101   a  is provided such that it can engage with the lifting plate rib  13   b . The slider boss  101   a  is provided to be movable between a position at which it presses the lifting plate rib  13   b  against the biasing force of the lifting plate spring  14  and a position at which it releases the pressure applied to the lifting plate rib  13   b . Accordingly, when the slider  101  reciprocates once, the lifting plate  13  pivots once about the pivot center  13   a.    
     Also as illustrated in  FIG. 2 , the engagement claw  102  is provided such that it can engage with the engagement boss (second engaged portion)  103   c  of the developing cartridge  103 . The engagement claw  102  is provided to be movable between a position at which it presses the engagement boss  103   c  against the biasing force of the cartridge spring  110  and a position at which it releases the pressure applied to the engagement boss  103   c . Accordingly, when the slider  101  reciprocates once, the developing cartridge  103  pivots once about the pivot center  103   a.    
     In the configuration described above, when a driving signal is input from the CPU to the second solenoid, the separation cam shaft  107  and the separation cam  100  rotate together a half turn in the CW direction. Accordingly, the slider  101  slides and the lifting plate  13  and the developing cartridge  103  operate in conjunction with each other. 
     The operation of the image forming apparatus  30  according to the first embodiment will now be described with reference to  FIG. 3 .  FIG. 3  is a cross-sectional view illustrating an operation of the image forming apparatus  30  according to the first embodiment. Note that the slider guide  106  is omitted in  FIG. 3  for the purpose of clearly illustrating the operation of the lifting plate  13 . 
       FIG. 3A  illustrates a print standby state of the image forming apparatus  30 . In the state illustrated in  FIG. 3A , the separation cam  100  is located at the first cam position, and the slider  101  is located at the first travel position. In this state, the lifting plate rib  13   b  of the lifting plate  13  biased by the lifting plate spring  14  is at rest while being in contact with the slider boss  101   a  of the slider  101 . At the same time, the engagement boss  103   c  of the developing cartridge  103  biased by the cartridge spring  110  is at rest while being in contact with the engagement claw  102  on the slider  101 . Also, the slider  101  is at rest while being in contact with the separation cam  100 . Accordingly, in the state illustrated in  FIG. 3A , the developing roller  103   b  and the photosensitive drum  8  are in a separated state, and the top sheet  1  on the lifting plate  13  and the feeding roller  3  are also in a separated state. 
     When a print job signal is first input from the host computer (not shown) connected to the image forming apparatus  30 , input of a driving signal from the CPU to the second solenoid causes the driving force of the motor M to be transmitted to the separation cam  100 . Thus, the separation cam  100  starts to rotate in the CW direction, and the slider  101  horizontally moves leftward in  FIG. 3 . When the slider  101  moves leftward, the engagement claw  102  on the slider  101  also moves leftward, so that the developing cartridge  103  pivots about the pivot center  103   a  in the CW direction. When the slider  101  moves leftward, the slider boss  101   a  of the slider  101  also moves leftward, so that the lifting plate  13  pivots about the pivot center  13   a  in the CW direction.  FIG. 3B  illustrates a state of the image forming apparatus  30  during rotation of the separation cam  100 . In the states illustrated in  FIGS. 3A and 3B , the slider  101  is subjected to the biasing force of the cartridge spring  110  in the leftward direction in the drawings. Thus, by the biasing force, the slider  101  is moved from the position shown in  FIG. 3A  to the position shown in  FIG. 3B . 
     The separation cam  100  stops rotating in the state of  FIG. 3C  reached by rotating backward from the state of  FIG. 3A . This causes the slider  101  to stop its leftward horizontal movement. In the state of  FIG. 3C , the separation cam  100  is located at the second cam position, and the slider  101  is located at the second travel position. In the state of  FIG. 3C , the pressure applied to the engagement boss  103   c  by the engagement claw  102  is released, and the pressure applied to the lifting plate rib  13   b  by the slider boss  101   a  is released. This allows the developing roller  103   b  biased by the cartridge spring  110  to come into contact with the photosensitive drum  8 , and allows the top sheet  1  on the lifting plate  13  biased by the lifting plate spring  14  to come into contact with the feeding roller  3 . That is, the developing roller  103   b  and the photosensitive drum  8  are in a contact state, and the top sheet  1  on the lifting plate  13  and the feeding roller  3  are in a contact state. 
     When the CPU inputs a driving signal to the first solenoid in the state of  FIG. 3C , the driving force of the motor M is transmitted to the feeding roller  3 . This causes the feeding roller  3  to rotate in the CW direction, thereby starting the operation of feeding the sheet  1 . As described above, an image is formed on the fed sheet  1  by being transferred and fixed. Then, the sheet  1  having the image formed thereon is discharged to the discharge tray  12 . In the first embodiment, it is possible to feed as many sheets  1  as needed without moving up and down the lifting plate  13  from the state illustrated in  FIG. 3C . 
     When the CPU inputs a driving signal to the second solenoid after the completion of the operation of feeding the sheet  1 , the separation cam  100  starts to rotate in the CW direction. Since the separation cam  100  rotates while pressing the slider  101  rightward in  FIG. 3 , the slider  101  moves rightward in  FIG. 3 . Together with the slider  101 , the engagement claw  102  and the slider boss  101   a  of the slider  101  move rightward in  FIG. 3 . Then, when the engagement claw  102  presses the engagement boss  103   c  against the elastic force of the cartridge spring  110 , the developing cartridge  103  pivots about the pivot center  103   a  in a counterclockwise (CCW) direction. Also, when the slider boss  101   a  presses the lifting plate rib  13   b  against the elastic force of the lifting plate spring  14 , the lifting plate  13  pivots about the pivot center  13   a  in the CCW direction.  FIG. 3D  illustrates a state of the image forming apparatus  30  during rotation of the separation cam  100 . 
     The separation cam  100  rotates backward in the CW direction from the state of  FIG. 3C  to return to the state of  FIG. 3A , where it stops rotating. This causes the slider  101  to stop its rightward horizontal movement, and thus causes the print job to end. Every time a print job signal is input, the image forming apparatus  30  of the first embodiment performs the above-described operation to form an image on the sheet  1 . 
     As described above, the first embodiment includes the separation cam (first moving member)  100  and the slider (second moving member)  101  as switching means for switching the positional relation between the lifting plate  13  and the feeding roller  3  and the positional relation between the developing roller  103   b  and the photosensitive drum  8 . The separation cam  100  and the slider  101  are operated by the motor M serving as a common driving source. Thus, with a simple configuration, the image forming apparatus of the first embodiment can switch the positional relation between the lifting plate  13  and the feeding roller  3  and the positional relation between the developing roller  103   b  and the photosensitive drum  8 . 
       FIG. 4  is a diagram showing a sequence in the image forming apparatus  30  described above. This sequence diagram shows a sequence carried out when a continuous print job signal for n sheets is input to the image forming apparatus  30 . In  FIG. 4 , the vertical axis shows mechanical components, and the horizontal axis represents time. 
     The states and positions of the mechanical components shown in  FIG. 4  will now be defined. The feeding roller  3  can take two states, a rotating (rotation) state and a non-rotating (stop) state. The developing cartridge  103 , the lifting plate  13 , the slider  101 , and the separation cam  100  each can take two stop positions, a separation position and a contact position, and operate between these positions. Note that the separation position is the position of each component in the state of  FIG. 3A , and the contact position is the position of each component in the state of  FIG. 3C . 
     The description of a sequence of operations from the input of a print job signal to the end of the print job, shown in ( 1 ) to ( 6 ) of  FIG. 4 , will be omitted here, as it is the same as the description of the operations described above. A point to be clearly described with reference to  FIG. 4  is that, for a continuous print job signal for n sheets, the lifting plate is moved up and down only once. 
     In a conventional example shown in  FIG. 9 , the lifting plate is moved up and down n times for a continuous print job signal for n sheets. On the other hand, in the configuration of the first embodiment, as shown in  FIG. 4 , the number of times the lifting plate is moved up and down can be reduced to once for each print job. It is thus possible to reduce noise associated with the up and down movement of the lifting plate during continuous printing, and to provide a quieter image forming apparatus. 
     In the first embodiment, after the completion of the print job, the components can be returned at any time to the positions in the print standby state shown in  FIG. 3A . The lifting plate  13  is located at a lower position in the state shown in  FIG. 3A . This allows the user to place additional sheets  1  and carry out a replacement operation, thereby making it possible to maintain high usability. Also, in the state shown in  FIG. 3A , the developing roller  103   b  is at rest at a distance from the photosensitive drum  8 . This can prevent deformation of the developing roller  103   b  and the photosensitive drum  8 . 
     Second Embodiment 
     A second embodiment will now be described. In the following description of the second embodiment, the same components and operations as those of the first embodiment may not be described. The second embodiment differs from the first embodiment in the location of the cartridge spring for generating a contact pressure between the photosensitive drum  8  and the developing roller  103   b.    
       FIG. 5  is a cross-sectional view illustrating an image forming apparatus according to the second embodiment. As in the first embodiment, an engagement claw  202  is provided on the slider  101 . The slider  101  is provided with a cartridge pressing member  203 . The cartridge pressing member  203  is biased by a cartridge spring  210  in the leftward direction in  FIG. 5 , and is provided to be movable with respect to the slider  101  in the right and left direction. The cartridge spring  210  is a compression spring, and the other end of the cartridge spring  210  engages with a component on the apparatus main body side. 
     The operation of the image forming apparatus according to the second embodiment will now be described.  FIG. 6  is a cross-sectional view illustrating an operation of the image forming apparatus according to the second embodiment. Note that the slider guide  106  is omitted in  FIG. 6  for the purpose of clearly illustrating the operation of the lifting plate  13 . 
     An overall operation of the second embodiment will not be described here, as it is the same as the first embodiment. The second embodiment differs from the first embodiment in the operation process where the lifting plate spring  14  and the cartridge spring  210  are compressed. 
     In the state illustrated in  FIG. 6A , the developing cartridge  103  is at rest, with the engagement boss  103   c  being in contact with the engagement claw  202  on the slider  101 . Since the cartridge pressing member  203  is not in contact with the engagement boss  103   c , the cartridge spring  210  is in a released state at this point. The lifting plate spring  14  is in a compressed state. 
     In the state illustrated in  FIG. 6C , the developing cartridge  103  is at rest, with the engagement boss  103   c  being pressed by the cartridge pressing member  203 . At this point, the cartridge pressing member  203  presses the engagement boss  103   c  and the cartridge spring  210  is in a compressed state. The lifting plate spring  14  is in a released state. 
     The first embodiment is configured such that, in the operation process from  FIG. 3C  to  FIG. 3A , the lifting plate spring  14  and the cartridge spring  110  are simultaneously brought into a compressed state (where the elastic force is being charged). Therefore, the first embodiment requires a driving torque for compressing the two elastic members, the lifting plate spring  14  and the cartridge spring  110 , against their elastic force, and hence requires a driving source and a power source that can provide the driving torque. 
     In the second embodiment, on the other hand, in the operation process from  FIG. 6A  to  FIG. 6C , the cartridge spring  210  is brought into a compressed state, whereas the lifting plate spring  14  is brought into a released state. In the operation process from  FIG. 6C  to  FIG. 6A , the lifting plate spring  14  is brought into a compressed state, whereas the cartridge spring  210  is brought into a released state. Therefore, the driving torque can be reduced in the second embodiment, as there is no need to provide the driving torque for compressing two springs in a single operation process. 
       FIG. 7  is a diagram showing a sequence in the second embodiment. This sequence diagram shows a sequence carried out when a continuous print job signal for n sheets is input to the image forming apparatus. In  FIG. 7 , the vertical axis shows mechanical components, and the horizontal axis represents time. 
     A point to be clearly described with reference to  FIG. 7  is that, in the second embodiment, the timing of compression of the lifting plate spring  14  differs from the timing of compression of the cartridge spring  210 . Thus, by separating the operation process which involves compression of the lifting plate spring  14  from the operation process which involves compression of the cartridge spring  210 , a reduction in driving torque can be achieved, as well as the advantageous effect of the first embodiment. The other description will be omitted, as it is the same as the description for  FIG. 4  in the first embodiment. 
     Accordingly, in the second embodiment, it is possible to use an inexpensive driving source and power source, and thus to provide an inexpensive image forming apparatus. 
     In the first and second embodiments described above, the switching means is configured to bring the developing roller  103   b  into contact with, and to separate it from, the photosensitive drum  8 . However, the present invention is not to be limited to this. That is, the present invention may be configured such that the positional relation between the developing roller  103   b  and the photosensitive drum  8  is switched between a first state where they are close in distance to each other and a second state where they are more distant from each other than in the first state. Even in this configuration, deformation of the developing roller  103   b  and the photosensitive drum  8  can be prevented by switching the positional relation between the developing roller  103   b  and the photosensitive drum  8  to the second state when no image formation is performed or during product distribution. Note that the first state described above does not necessarily refer to a state where the developing roller  103   b  and the photosensitive drum  8  are in contact, and the second state does not necessarily refer to a state where the developing roller  103   b  and the photosensitive drum  8  are separated from each other. 
     Similarly, the present invention is not to be limited to the configuration where the top sheet  1  on the lifting plate and the feeding roller  3  are brought into contact with, and separated from, each other. That is, the present invention may be configured such that the positional relation between the lifting plate  13  and the feeding roller  3  is switched between a state (first state) where they are close in distance to each other and a state (second state) where they are more distant from each other than in the first state. 
     Since the first and second embodiments are configured to move the lifting plate  13  up and down using the slider  101  that horizontally moves, it is possible to increase the amount of sheets  1  that can be supported. In the configuration of a conventional example illustrated in  FIG. 8 , to support a larger amount of sheets  1 , the outermost diameter of a feeding cam  400  needs to be increased to increase the pivot angle of a lifting plate  413 . However, increasing the outermost diameter of the feeding cam  400  may cause interference of a developing cartridge  403  with a rotation path  400   a  (indicated by a broken line) of the feeding cam  400 . To avoid the interference, it is necessary to increase the size of the image forming apparatus in the height or width direction. 
     On the other hand, the first and second embodiments do not require the feeding cam  400 , as the slider  101  has the function of causing the lifting plate  13  to pivot. That is, it is possible to provide an image forming apparatus that can support a larger amount of sheets  1 , without increasing the size of the main body. 
     According to the present invention, the switching means switches, by the driving force, the positional relation between the supporting member and the feeding member and the positional relation between the developing member and the photosensitive member. It is thus possible to provide an image forming apparatus that can switch, with a simple configuration, the positional relation between the supporting member and the feeding member and the positional relation between the photosensitive member and the developing member. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of International Patent Application No. PCT/JP2015/059595, filed Mar. 27, 2015, which is hereby incorporated by reference herein in its entirety.