Patent Publication Number: US-7708269-B2

Title: Sheet feeding device and image forming apparatus

Description:
CROSS REFERENCE 
   This Nonprovisional application claims priority under 35 U.S.C. §119(a) on patent application Ser. No. 2005-053837 filed in Japan on Feb. 28, 2005, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to sheet feeding devices, such as large capacity cassettes (hereinafter merely referred to as LCCs), adapted for use in sheet processing apparatus, such as image forming apparatus, to store therein a large number of sheets to be fed into the apparatus. The present invention further relates to image forming apparatus provided with such sheet feeding devices. 
   Conventional sheet feeding devices are positioned beside sheet processing apparatus for storing sheets of a size that is most frequently used therein. For example, LCCs adapted for use in copying machines as image forming apparatus generally have a capacity of approximately 2,000 sheets of A4-size plain paper placed in landscape orientation. 
   Designed for multipurpose use and to perform various functions such as of printing or facsimile communication, recent image forming apparatus tend to handle an increasing number of sheets of various sizes and types. 
   In light of the foregoing, there have been developed LCCs with a capacity of 4,000 or more sheets of various sizes. With 4,000 to 5,000 sheets of A3-size plain paper stored therein, such LCCs have a total weight of approximately 100 kg. 
   On the other hand, there has been strong demand for smaller and lighter image forming apparatus. Suppose an image forming apparatus is provided with an LCC. The LCC includes a sheet stacker for stacking sheets, and the sheet stacker is removable from a housing of the LCC. When the sheet stacker with a large number of sheets stacked therein is pulled out of, or pushed into, the housing, the impact of collision between the sheet stacker and the housing causes the image forming apparatus to vibrate or move. Such vibration or movement causes components inside the image forming apparatus to become loosely mounted or prevents the image forming apparatus from being maintained in a horizontal position. 
   To solve the foregoing problems, JP H11-208902A discloses an LCC that has an elastic member arranged in a housing so as to face a rear side surface of a sheet stacker. The elastic member is intended to cushion an impact of collision caused between the housing and the sheet stacker when the stacker is moved. JP 2003-267565A discloses an LCC that has a housing with an openable upper surface. The openable upper surface allows access to a sheet stacker from above, thereby eliminating the need to remove the sheet stacker from the housing for sheet replenishment or any other operation. 
   However, it is hard to determine an optimum shape, material, size, etc., for the elastic member in order to ensure that the elastic member cushions the impact of collision between the housing and the sheet stacker. Also, the construction as disclosed in JP 2003-267565A involves complicated arrangement of sheet feeding members and also makes it difficult to stack sheets in the sheet stacker without causing damage, such as bent corners, to the sheets. 
   A feature of the invention is to provide an LCC that ensures that a collision impact on a sheet processing apparatus is cushioned with a damping member provided in a sheet stacker. The damping member is adapted to act on the sheet stacker a damping force according to moving speed of the sheet stacker as being moved in and out of a housing of the LCC. Another feature of the invention is to provide an image forming apparatus that prevents components therein from becoming loosely mounted and is allowed to be maintained in a horizontal position. 
   SUMMARY OF THE INVENTION 
   A sheet feeding device of the invention includes a stacking plate, a sheet stacker, and a damping member. The stacking plate is liftably supported in the sheet stacker and is adapted for sheets to be fed into a sheet processing apparatus to be stacked thereon. The sheet stacker is adapted to be movable between a housed position where the sheet stacker is housed in a housing and an exposed position where the sheet stacker is exposed outside of the housing. The damping member is adapted to exert on the sheet stacker a damping force according to moving speed of the sheet stacker. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional view of an image forming apparatus as a sheet processing apparatus into which an LCC according to an embodiment of the invention is to feed sheets; 
       FIG. 2  is a schematic front cross-sectional view of the LCC; 
       FIG. 3  is a schematic side cross-sectional view of the LCC with a sheet stacker in a housed position; 
       FIG. 4  is a schematic side cross-sectional view of the LCC in the course of the sheet stacker being moved between the housed position to an exposed position; and 
       FIG. 5  is a schematic side cross-sectional view of the LCC with the sheet stacker in the exposed position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the accompanying drawings, embodiments of the invention are described below. Referring to  FIG. 1 , an LCC  1  as the sheet feeding device of the invention is arranged beside an image forming apparatus  100  as a sheet processing device of the invention. Instead of the single LCC  1  in a first embodiment, a plurality of LCCs may be arranged in alignment with one another. The LCC  1  feeds a sheet P of paper, or another material such as OHP film, into the image forming apparatus  100 . 
   The image forming apparatus  100  forms an image on the sheet P by performing an electrophotographic image forming process. The image forming apparatus  100  has sheet cassettes  101  to  104  and a sheet output tray  105  in a bottom portion and a top portion thereof, respectively. A sheet transport path F 1  is provided so as to lead from the sheet cassettes  101  to  103  to the sheet output tray  105 . A photoreceptor drum  106  is positioned close to the sheet transport path F 1 . Around the photoreceptor drum  106  arranged are a charging device  107 , an optical scanning unit  108 , a developing unit  109 , a transferring device  110 , a cleaning unit  111 , and the like. 
   Registration rollers  112  are provided upstream of the photoreceptor drum  106  along the sheet transport path F 1 . The registration rollers  112  feed the sheet P to a transfer area located between the photoreceptor drum  106  and the transferring device  110  in synchronization with rotation of the photoreceptor drum  106 . A fusing device  113  is provided downstream of the photoreceptor drum  106  along the sheet transport path F 1 . 
   The charging device  107  applies a predetermined level of electrostatic charge to a circumferential surface of the photoreceptor drum  106 . The optical scanning unit  108  forms an electrostatic latent image on the circumferential surface of the photoreceptor drum  106  based on image data. The developing unit  109  supplies toner to the circumferential surface and develops the electrostatic latent image into a toner image. The transferring device  110  transfers the toner image as formed on the circumferential surface to the sheet P. The fusing device  111  fixes the toner image onto the sheet P. The sheet P with the toner image fixed thereto is output to the sheet output tray  105 . The cleaning unit  111  removes and collects residual toner that remains on the circumferential surface after the transfer operation is completed. 
   The image forming apparatus  100  is also provided with a switchback transport path F 2  and a sheet transport path F 3 . In a duplex image forming process in which an image is formed on each side of sheet P, the sheet P with an image formed on a first side is transported on the switchback transport path. F 2  to the transfer area with the first side and a second side reversed. Sheets fed from each of the sheet cassette  104 , a manual feeding tray  114 , and a sheet receiving section  115  are transported on the sheet transport path F 3 . The tray  114  is provided on a side surface of the image forming apparatus  100  for feeding sheets of various sizes. The section  115  is provided for receiving sheets fed from the LCC  1 . The path F 3  extends approximately horizontally so as to join, at one end, the path F 1  at an upstream point of the registration rollers  112  and be divided, at the other end, to lead to each of the sheet cassette  104 , the tray  114 , and the section  115 . 
   Referring to  FIG. 2 , the LCC  1  includes a housing  1 A, a sheet stacker  2 , a pick-up roller  3 , a feeding roller  4 , a reversing roller  5 , and transporting rollers  6 . 
   The sheet stacker  2  has a stacking plate  21 , a front guiding plate  22 , side guiding plates  23  and  24 , and a rear guiding plate. The side guiding plate  24  and the rear guiding plate are not shown in the figure. Held in a horizontal position, the stacking plate  21  is provided for a plurality of sheets to be stacked thereon. The sheets as stacked are positioned by the front guiding plate  22 , the side guiding plates  23  and  24 , and the rear guiding plate. 
   The pick-up roller  3  is supported pivotably about a rotary shaft for the feeding roller  4  between an upper position and a lower position. The pick-up roller  3  picks up a top one of sheets stacked on the stacking plate  21  in order to lead the top sheet between the feeding roller  4  and the reversing roller  5 . 
   The rollers  4  and  5  are both rotated clockwise in  FIG. 2  to allow passage of the sheet therebetween. In a case where multiple sheets are picked up at a time and led between the rollers  4  and  5  by the roller  3 , only a top one of the sheets are brought into contact with the roller  4  and led to the transporting rollers  6 . The rest of the sheets are returned to the stacking plate  21  by the reversing roller  5 . 
   The LCC  1  has a capacity of a large number of sheets (approximately 5,000 sheets in the present embodiment) of various sizes such as of A3, B4, A4, and B5. 
   The side guiding plates  23  and  24  are rendered movable on the stacking plate  21  within a predetermined range from frontward to rearward, and vice versa, of the LCC  1 . More specifically, the plates  23  and  24  are rendered movable in two opposite directions perpendicular to a sheet feeding direction. Movement of one of the plates  23  and  24  in one of the two directions is transmitted to the other, so that the other is moved in the opposite direction. Accordingly, sheets stacked on the-stacking plate  21  are positioned approximately at the center of the stacking plate  21  along the opposite directions. In addition, the rear guiding plate is rendered movable within a predetermined range from side to side of the LCC  1 , i.e., movable along the sheet feeding direction. 
   The sheet stacker  2  has a lifting motor in the rear side surface. Rotation of the lifting motor is transmitted through wire, so that the stacking plate  21  is lifted up and down along a not-shown guiding shaft while being held in a horizontal position. 
   Inside the LCC  1 , there are provided slide rail assemblies  7  and  8 . The slide rail assembly  7  includes a sliding member  7 A, an intermediate member  7 B, and a fixed member  7 C. The slide rail assembly  8  includes a sliding member  8 A, an intermediate member  8 B, and a fixed member  8 C. The sliding members  7 A and  8 A are attached to the right and left outer side surfaces of the sheet stacker  2 , respectively. The fixed members  7 C and  8 C are attached to the right and left inner side surfaces of the housing  1 A, respectively. 
   There are ball bearings arranged between the sliding member  7 A and the intermediate member  7 B and between the intermediate member  7 B and the fixed member  7 C, respectively. The sliding member  7 A is slidable from frontward to rearward, and vice versa, of the LCC  1  with respect to the intermediate member  7 B. Further, the intermediate-member  7 B is slidable from frontward to rearward, and vice versa, of the LCC  1  with respect to the fixed member  7 C. The slide rail assembly  8  has a similar construction to that of the assembly  7 . The slide rail assemblies  7  and  8  allow the sheet stacker  2  to be detachably housed in the housing  1 A. The sheet stacker  2  is movable between a housed position and an exposed position. In the housed position, the sheet stacker  2  is housed, and the stacking plate  21  is concealed, in the housing  1 A. In the exposed position, the entire stacking plate  21  is exposed at the front of the housing  1 A. 
   At a front portion of a bottom surface thereof, the sheet stacker  2  has a wheel  26  mounted rotatably. When the sheet stacker  2  is in the housed position, a circumferential surface of the wheel  26  is out of contact with a floor surface. In the course of the sheet stacker  2  being moved from the housed position to the exposed position, the circumferential surface is brought into contact with the floor surface with the weight of the sheet stacker  2 . 
   When the sheet stacker  2  is pulled out from the housed position to the exposed position, the sliding member  7 A together with the intermediate member  7 B is first slid frontward with respect to the fixed member  7 C. Then, when the sheet stacker  2  is still pulled after the intermediate member  7 B is slid a maximum sliding distance with respect to the fixed member  7 C, the sliding member  7 A is slid further frontward with respect to the intermediate member  7 B. Thus, a maximum pullout distance of the sheet stacker  2  is a sum of the maximum sliding distance of the intermediate member  7 B with respect to the fixed member  7 C and a maximum sliding distance of the sliding member  7 A with respect to the intermediate member  7 B. 
   When the sheet stacker  2  is pushed in from the exposed position to the housed position, the intermediate member  7 B is first slid with respect to the fixed member  7 C, with the sliding member  7 A projecting frontward. Then, when the sheet stacker  2  is still pushed after the intermediate member  7 B is slid a maximum sliding distance with respect to the fixed member  7 C, the sliding member  7 A is slid further into the housing  1 A with respect to the intermediate member  7 B. The slide rail assembly  8  is slid in a similar manner when the sheet stacker  2  is pulled out or pushed in. 
     FIGS. 3 to 5  are schematic side cross-sectional views of the LCC  1 . Illustrated in  FIGS. 3 to 5  is the sheet stacker  2  in the housed position, in the course of being moved between the housed position and the exposed position, and in the exposed position, respectively. 
   A pinion gear  11  and an intermediate gear  12  are rotatably mounted on the left inner side surface of the housing  1 A. A centrifugal clutch  13  is also mounted on the left inner side surface. 
   The maximum pullout distance of the sheet stacker  2  is a sum of-a maximum sliding-distance of the intermediate member  8 B with respect to the fixed member  8 C and a maximum sliding distance of the sliding member  8 A with respect to the intermediate member  8 B. The maximum pullout distance is approximately equal to length of the sheet stacker  2  as measured along a moving direction thereof, i.e., depth of the sheet stacker  2 . Also, the maximum sliding distance of the intermediate member  8 B with respect to the fixed member  8 C is approximately equal to the maximum sliding distance of the sliding member  8 A with respect to the intermediate member  8 B. Therefore, full length of the slide rail assembly  8  as measured along the moving direction is approximately half of the depth of the sheet stacker  2 . The sliding member  8 A is positioned so as to extend rearward from an approximately horizontally central portion of the left outer side surface of the sheet stacker  2 . The fixed member  8 C is positioned so as to extend rearward from an approximately horizontally central portion of the left inner side surface of the housing  1 A. 
   The centrifugal clutch  13  corresponds to the damping member of the invention. The centrifugal clutch  13  includes an input shaft gear  13 A, an output shaft  13 B, clutch shoes  13 C, and a rotatable plate  13 D. 
   The intermediate gear  12  has a small gear  12 A and a large gear  12 B fixed coaxially to each other. The small gear  12 A meshes with the pinion gear  11 . The large gear  12 B meshes with the input shaft gear  13 A. The output shaft  13 B is fixed to the left inner side surface of the housing  1 A. 
   A rack gear  9  is formed on an upper surface of the sliding member  8 A along the length thereof. The rack gear  9  has teeth that are shaped and pitched so as to mesh with the pinion gear  11 . Thus, the rack gear  9  is positioned so as to extend rearward from an approximately horizontally central portion of the left outer side surface of the sheet stacker  2 . 
   The pinion gear  11  is rotatably supported at an approximately horizontally central portion of the left inner side surface of the housing  1 A. The positioning of the rack gear  9  allows the gear  9  to mesh with the pinion gear  11  in the beginning of pullout action of the sheet stacker  2  and in the end of housing action of the stacker  2 . 
   The mesh between the rack gear  9  and the pinion gear  11  translates the sliding movement of the slide rail assembly  8  frontward or rearward of the LCC  1  into rotation of the pinion gear  11 . The rotation of the pinion gear  11  is transmitted to the input shaft gear  13 A through the intermediate gear  12 . The rack gear  9  and the pinion gear  11  collectively correspond to the transmitting member of the invention. 
   Referring back to the centrifugal clutch  13 , the clutch shoes  13 C are slidably mounted on the rotatable plate  13 D. The input shaft gear  13 A is fixed to the rotatable plate  13 D. When the input shaft gear  13 A is spun together with the rotatable plate  13 D and the clutch shoes  13 C, the shoes  13 C are centrifugally slid outward and come into contact with an inner circumferential surface of the output shaft  13 B. Friction between the clutch shoes  13 C and the output shaft  13 B acts as a damping force on the rotatable plate  13 D and the input shaft gear  13 A, so that the rotation of the pinion gear  11  and the movement of the rack gear  9  are slowed down. 
   Consequently, the movement of the sheet stacker  2  is also slowed down in the beginning of the pullout action, and in the end of the housing action. 
   When the sheet stacker  2  is to be pulled out of the housing  1 A, more specifically, the damping force acts on the movement of the stacker  2  in the course of the stacker  2  in a position shown in  FIG. 3  being pulled out in a direction of arrow X to reach a position shown in  FIG. 4  (intitial stage). The damping force does not act on the movement in the course of the stacker  2  in the position shown in  FIG. 4  reaching a position shown in  FIG. 5 . 
   When the sheet stacker  2  is to be pushed into the housing  1 A, in contrast, the damping force does not act on the movement of the stacker  2  in the course of the stacker  2  in the position shown in  FIG. 5  being pushed in a direction of arrow Y to reach the position shown in  FIG. 4 . The damping force acts on the movement in the course of the stacker  2  in the position shown in  FIG. 4  reaching the position shown in  FIG. 3  (final stage). 
   Accordingly, even if the sheet stacker  2  in the position shown in  FIG. 3  or  5  is pulled out or pushed in with a strong force, the sheet stacker  2  is moved at a comparatively low speed while most portions thereof are positioned inside the housing  1 A. This prevents the movement of the sheet stacker  2  from exerting a strong inertial force, or causing a large collision impact, on the housing  1 . 
   Referring back to the centrifugal clutch  13 , the centrifugal force that acts on the clutch shoes  13 , and the friction caused between the shoes  13  and the output shaft  13 D, both depend on the rotation speed of the input shaft gear  13 A. In addition, the rotation speed of the input shaft gear  13 A is proportional to moving speed of the sheet stacker  2 . Thus, a damping force according to the moving speed acts on the sheet stacker  2 . More specifically, the movement of the stacker  2  is hardly damped at a low moving speed and strongly damped at a high moving speed. 
   This ensures that a collision impact on the image forming apparatus  100  is cushioned. This prevents components in the image forming apparatus  100  from becoming loosely mounted and also allows the apparatus  100  to be maintained in a horizontal position. 
   Alternatively, the pinion gear  11  is mounted on the left inner side surface of the housing  1 A at a position more rearward than that as shown in  FIG. 3 . This positioning contributes to a shortened duration of the damping force acting on the sheet stacker  2 . Further alternatively, the rack gear  9  is rendered shorter in order to shorten the duration. Contrary, the rack gear  9  is rendered longer so as to extend more rearward, in order to prolong the duration. 
   The LCC  1  according to the present embodiment is fit for use not only in the image forming apparatus  100  but also in any sheet processing apparatus that is adapted to perform certain processes to sheets to be fed thereinto from the LCC  1 . 
   Instead of the centrifugal clutch  13  as the damping member in the LCC  1 , another device may be used as long as such device exerts on the sheet stacker  2  a damping force according to moving speed of the stacker  2 . 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.