Abstract:
A gear engagement mechanism of a life device includes a lifting member interlocking with a lifting tray to linearly move in a vertical direction, and a gear train having a pinion engaged with the rack to transmit a rotary motion to the rack and transmitting the rotation torque of a lift motor M to the pinion. When the lifting member has over-run an upper limit stop position and a lower limit stop position, engagement of the pinion and the rack is released.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-078306 filed on Apr. 7, 2015, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    The technology of the present disclosure relates to an image forming apparatus such as a copy machine and a printer and a paper feeding device constituting a part thereof. 
         [0003]    In a paper feeding device, one end of a lifting tray is connected to a paper feeding tray, on which papers to be fed are placed, so as to be rotatable. Furthermore, in the paper feeding device, a shaft is arranged at a lower side of the lifting tray, and one end of a lift plate is integrally and rotatably connected to the shaft and abuts and supports the other end side of the lifting tray side from below at the other end of the lift plate. Furthermore, the shaft is rotated by the start of a lift motor to rise the lift plate, so that the lifting tray is lifted up and thus the papers placed on the paper feeding tray are sent from the paper feeding tray by a pickup roller one by one. 
       SUMMARY 
       [0004]    A paper feeding device according to one aspect of the present disclosure includes a paper feeding tray, a lifting tray, and a lift device. On the aforementioned paper feeding tray, a paper to be fed is placed. The aforementioned lifting tray has one end connected to the aforementioned paper feeding tray so as to be rotatable and holds the paper from below. The aforementioned lift device is provided corresponding to the other end side of the aforementioned lifting tray. Furthermore, the lift device lifts up and down the aforementioned lifting tray via a gear engagement mechanism driven by rotation torque of a lift motor. 
         [0005]    The aforementioned gear engagement mechanism includes a lifting member and a gear train. The aforementioned lifting member has a rack. Furthermore, the lifting member interlocks with the aforementioned lifting tray to linearly move in a vertical direction. The aforementioned gear train has a pinion engaged with the aforementioned rack to transmit a rotary motion to the rack. Furthermore, the gear train transmits the rotation torque of the aforementioned lift motor to the pinion. When the aforementioned lifting member has over-run an upper limit stop position and a lower limit stop position, engagement of the aforementioned pinion and the aforementioned rack is released. 
         [0006]    An image forming apparatus according to another aspect of the present disclosure includes the aforementioned paper feeding device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a block diagram illustrating a configuration of an image forming apparatus. 
           [0008]      FIG. 2  is a perspective view of a paper feeding device before a lifting tray is risen. 
           [0009]      FIG. 3  is a perspective view of a paper feeding device after a lifting tray is risen. 
           [0010]      FIG. 4  is an enlarged perspective view of a lifting tray before being risen and a lift device. 
           [0011]      FIG. 5  is an enlarged perspective view of a lift device in the state in which a lifting member has been lowered. 
           [0012]      FIG. 6  is an enlarged perspective view of a lift device in the state in which a lifting member has risen. 
           [0013]      FIG. 7  is a perspective view of a lifting member. 
           [0014]      FIG. 8  is a perspective view when  FIG. 5  is viewed in a direction A. 
           [0015]      FIG. 9  is a perspective view taken along line B-B of  FIG. 8 . 
           [0016]      FIG. 10A  is an explanation diagram illustrating a positional relation between a rack and a pinion when a lifting member has over-run a lower limit stop position. 
           [0017]      FIG. 10B  is an explanation diagram illustrating a positional relation between a rack and a pinion when a lifting member has over-run an upper limit stop position. 
           [0018]      FIG. 11  is a diagram corresponding to  FIG. 8  in another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Hereinafter, one example of an embodiment will be described in detail on the basis of the drawings. It is noted that the technology of the present disclosure is not limited to the following embodiment. 
         [0020]      FIG. 1  illustrates an image forming apparatus  1  such as a laser printer and a multifunctional peripheral, wherein the image forming apparatus  1  is configured to form an image on a paper on the basis of image data transmitted from a terminal and the like (not illustrated) while conveying the paper. The image forming apparatus  1  includes a paper feeding unit  2 , an image forming unit  3 , a fixing unit  4 , and a paper discharge unit  5 . 
         [0021]    The paper feeding unit  2  is a cassette paper feeding unit or a manual paper feeding tray that supplies a paper to the image forming unit  3 . The image forming unit  3  includes a developing device  6 , a photosensitive drum  7  and the like. In the image forming unit  3 , an electrostatic latent image is formed on the photosensitive drum  7  by an optical scanning device (not illustrated) and is developed as a tone image by the developing device  6 . The toner image is transferred to a paper supplied from the paper feeding unit  2 . The fixing unit  4  includes a fixing roller and a pressure roller (not illustrated) and fixes the toner image, which has been transferred to the paper in the image forming unit  3 , to the paper. In this way, an image is formed on the paper. The paper with the formed image is discharged to the paper discharge unit  5  from the fixing unit  4 . 
         [0022]    Moreover, the image forming apparatus  1  includes a toner container  8  and a toner collection device  9 . The toner container  8  receives toner as a developer to be supplied to the developing device  6 . The toner collection device  9  collects toner remaining on the photosensitive drum  7 . 
         [0023]      FIG. 2  and  FIG. 3  illustrate a paper feeding device  33  constituting the paper feeding unit  2 , wherein the paper feeding device  33  includes a manual paper feeding tray  10  on which papers (not illustrated) to be fed are placed. 
         [0024]    On the paper feeding tray  10 , one end of a lifting tray is connected to be rotatable by a shaft  12 . The lifting tray  11  holds a part of the paper from below. The other end of the lifting tray  11 , for example, is supported from below by an urging part (not illustrated). 
         [0025]    At an approximate center portion of an upper side of the other end side (the right end side of  FIG. 2  and  FIG. 3 ) of the lifting tray  11 , a pick-up roller (not illustrated) is arranged. A paper positioned on the uppermost surface of the lifting tray  11  is taken out by a rotating operation of the pick-up roller and is sent to the photosensitive drum  7  side. 
         [0026]    A lift device  15  is provided corresponding to the other end side (the right end side of  FIG. 2  and  FIG. 3 ) of the lifting tray  11 . As illustrated in  FIG. 4 , the lift device  15  includes a lift motor M arranged at a lower end side of a receiving case  16  and a gear engagement mechanism  17  arranged above the lift motor M. Furthermore, the lift device  15  lifts up and down the lifting tray  11  via the gear engagement mechanism  17  driven by rotation torque of the lift motor M. 
         [0027]    In detail, the gear engagement mechanism  17  includes a lifting member  18 . The lifting member  18  is provided with a rack  19  having a plurality of tooth parts  19   a  (see  FIG. 7 ) vertically arranged in a straight line. At the lateral side of the rack  19 , a gear train  20  is arranged. The gear train  20  includes a first gear  21 , a second gear  22 , and a third gear  23  engaged with one another. The first gear  21 , the second gear  22 , and the third gear  23  are sequentially arranged from below and a pinion  24  engaged with the tooth parts  19   a  of the rack  19  is coaxially mounted with the third gear  23 . 
         [0028]    At an output shaft of the lift motor M, a worm gear ml engaged with the first gear  21  is fixed. The rotation torque of the lift motor M is transmitted to the rack  19  via the worm gear ml, the first gear  21 , the a second gear  22 , the third gear  23 , and the pinion  24 . Furthermore, the rack  19  linearly moves the lifting member  18  up and down. 
         [0029]    As illustrated in  FIG. 7 , the lifting member  18  includes a slider  25 . From an upper end of one surface of the slider  25 , an abutting piece  26  protrudes. In a surface of the slider  25  opposite to the abutting piece  26 , a large groove  27  and a small groove part  28  vertically extending are provided in parallel to each other, and at a lateral side of the small groove part  28 , the rack  19  is provided in parallel to the small groove part  28 . 
         [0030]    As illustrated in  FIG. 5 ,  FIG. 6 ,  FIG. 8 , and  FIG. 9 , the gear engagement mechanism  17  is covered by a cover plate  29  having a slide rail  29   a  vertically extending. The slide rail  29   a  is inserted into the small groove part  28  of the lifting member  18  so as to be vertically movable. 
         [0031]    The abutting piece  26  of the lifting member  18  faces an upper surface of a right end portion of the lifting tray  11  in  FIG. 4 . Furthermore, the lifting tray  11  is pushed up by urging force of the urging part, so that the abutting piece  26  abuts the upper surface of the right end portion of the lifting tray  11  in  FIG. 4  and thus the lifting member  18  operates so as to be integrally movable with the lifting tray  11 . In this way, the rotation torque of the lift motor M is transmitted to the gear engagement mechanism  17 , so that the lifting tray is lifted up and down. 
         [0032]    In a paper feeding state, as illustrated in  FIG. 3  and  FIG. 6 , the lifting tray  11  rises, so that an upper surface of a paper on the lifting tray  11  abuts the pick-up roller. On the other hand, in a non-paper feeding state, as illustrated in  FIG. 2  and  FIG. 5 , the lifting tray  11  falls, so that a paper and the pick-up roller are separated from each other. 
         [0033]    From the large groove  27  of the lifting member  18 , a pressing piece  30  as illustrated in  FIG. 9  protrudes. At a protruding end of the pressing piece  30 , an inclination part  30   a  inclined downwardly to the right side of  FIG. 9  is formed. 
         [0034]    On the other hand, at the receiving case  16  side, a switch mounting part  31  is formed corresponding to the lifting member  18 . The switch mounting part  31  is provided with a push switch  32  as a detection part that detects the remaining amount of papers on the paper feeding tray  10  on the basis of a rising position of the lifting tray  11 . The push switch  32  is mounted at a position corresponding to the large groove  27 . 
         [0035]    When the remaining amount of papers on the paper feeding tray  10  is 100%, the push switch  32  is pressed by an upper end of the pressing piece  30  and enters an OFF state.  FIG. 9  illustrates the state in which the upper end of the pressing piece  30  has interfered with the push switch  32 , and actually illustrates the state in which the push switch  32  has been pushed by the pressing piece  30  and sunk down. When the lifting member  18  rises with a reduction of the remaining amount of papers on the paper feeding tray  10 , the pressing piece  30  is upwardly away from the push switch  32 , so that the push switch  32  protrudes. Furthermore, when the remaining amount of papers, for example, is reduced to 30%, since the pressure by the pressing piece  30  is released, the push switch  32  is turned ON, so that an ON signal (a remaining amount detection signal) is inputted to a control unit (not illustrated). In this way, it is determined that the remaining amount of papers, for example, has been reduced to 30%. During this period, the lifting tray  11  is inclined with respect to the upper surface of the paper feeding tray  10  and rises to a raised posture of  FIG. 3  from a horizontal posture of  FIG. 2  in which it has laid along the upper surface of the paper feeding tray  10 . 
         [0036]    At this time, for example, when an unexpected operation occurs in the lift motor M due to a trouble of a control system and the pinion  24  is not stopped and over-rotates clockwise in  FIG. 10B , the lifting member  18  (the rack  19 ) over-runs an upper limit stop position with momentum and thus the pinion  24  is not engaged with the tooth parts  19   a  of the rack  19  (see  FIG. 10B ). In contrast, when the pinion  24  over-rotates counterclockwise in  FIG. 10A , the lifting member  18  (the rack  19 ) over-runs a lower limit stop position and thus the pinion  24  is not also engaged with the tooth parts  19   a  of the rack  19  (see  FIG. 10A ). 
         [0037]    As described above, in the present embodiment, in the lift device  15  that lifts the lifting tray  11  up and down, a rack and pinion has been employed as the gear engagement mechanism  17  that transmits the rotation torque of the lift motor M to the lifting tray  11 . Furthermore, when the lifting member  18  has over-run the upper limit stop position and the lower limit stop position with momentum, the engagement of the pinion  24  and the rack  19  is released. Consequently, it is possible to prevent the rotation torque of the lift motor M from being transmitted to the rack  19 , that is, the lifting member  18 . 
         [0038]    In this way, it is possible to achieve a small and simple configuration, and to prevent parts of the gear engagement mechanism  17  from being broken even when an unexpected operation has occurred in the lift motor M due to a trouble of a control system, for example. Consequently, it is possible to achieve the paper feeding device  33  with high reliability and thus to enhance the reliability of the image forming apparatus  1 . 
         [0039]    In addition, as illustrated in  FIG. 11 , when three push switches  32  are vertically provided spaced apart from one another, it is possible to minutely detect the number of papers remaining on the paper feeding tray  10 . In this case, the front end of the pressing piece  30 , for example, is configured to have a shape (not illustrated) curved in a protruding shape so as to be able to press each push switch  32 . It is sufficient if the number of push switches  32  is increased and decreased according to necessity. 
         [0040]    As described above, the present invention is useful for a paper feeding device and an image forming apparatus including the same.