Patent Publication Number: US-7588243-B2

Title: Sheet feeding apparatus and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a sheet feeding apparatus and an image forming apparatus, and more particularly, to a sheet feeding apparatus and an image forming apparatus including a plurality of sheet containing devices mounted one above another with an overlap in a vertical direction. 
   2. Related Background Art 
   Up to now, in an image forming apparatus provided with a sheet feeding apparatus including a sheet containing device such as a sheet feeding cassette, sheets are stacked on a plurality of sheet feeding cassettes which are detachably mounted to an apparatus main body one above another with an overlap in a vertical direction, and are sequentially fed to an image forming portion, and then an image is formed on a sheet at the image forming portion. 
   In such the image forming apparatus, as disclosed in Japanese Patent Application Laid-open No. H07-61613, sheets with different sizes are contained correspondingly in the plurality of sheet feeding cassettes mounted one above another with an overlap in a vertical direction, and the sheets are selectively fed to an image forming portion from the plurality of sheet feeding cassettes according to a designated size of the sheet. 
     FIG. 6  shows a structure of a conventional image forming apparatus including a plurality of (two) sheet feeding cassettes overlapping with each other in the vertical direction. An upper and lower sheet feeding cassettes  105  and  109  are detachably contained in a width direction with respect to the apparatus main body  100  by a cassette drawer device  108  and  112  for slidably holding the sheet feeding cassettes  105  and  109  in a direction orthogonal to a sheet feeding direction (hereinafter referred to as “width direction”). 
   Sheets S contained in the sheet feeding cassettes  105  and  109  are fed out by sheet feeding rollers  106  and  110  which are driven by a driving transmission apparatus to be rotated, and then are separated one by one by separating units  107  and  111 . After that, the separated sheets are conveyed to an image forming unit  104 . It should be noted that in  FIG. 6 , a partition plate  113  partitions the upper sheet feeding cassette  105  and the lower sheet feeding cassette  109 . The lower sheet feeding roller  110  is positioned below the partition plate  113 , that is, below a bottom of the upper sheet feeding cassette  105 . 
   It should be noted that the cassette drawer devices  108  and  112 , which detachably accommodate the sheet feeding cassettes  105  and  109  arranged in the vertical direction, has a structure as shown in  FIGS. 7A ,  7 B, and  7 C.  FIG. 7A  is a front view showing the cassette drawer device  108 ,  112  viewed from a direction toward which the cassette is drawn out therefrom.  FIGS. 7B and 7C  are perspective views showing a state in which the sheet feeding cassette  105 ,  109  is mounted in the cassette drawer device  108 ,  112  and a state in which the sheet feeding cassettes  105 ,  109  are drawn out from the-cassette drawer device  108 ,  112 , respectively. 
   As shown in  FIGS. 7A to 7C , the cassette drawer device  108  ( 108 L and  108 R),  112  ( 112 L and  112 R) is arranged outside the sheet feeding cassette  105 ,  109 , and includes a base member  108   a ,  112   a  that is fixed on a front-and-rear side plate  100   a ,  100   b  of the apparatus main body  100  (refer to  FIG. 6 ) and a slide member  108   b ,  112   b  that is slidably held in the base member  108   a ,  112   a.    
   The sheet feeding cassette  105 ,  109  is mounted to the slide member  108   b ,  112   b , thereby being detachably mounted into the apparatus main body  100  through the intermediation of the cassette drawer device  108 ,  112 . 
   However, in such the conventional sheet feeding apparatus and the image forming apparatus, when the plurality of sheet feeding cassettes are provided one above another with an overlap in a vertical direction, a height of the apparatus main body increases. When the height of the apparatus main body thus increases, for example, in a case of a multifunction printer provided with a scanner or the like on a top surface of the apparatus main body, there is a problem in that a position of an original table for stacking an original is higher, and operability thereof deteriorates. 
   On the other hand, in the conventional image forming apparatus, a sheet feeding unit provided with sheet feeding rollers  106  and  110  is fixed to a feed frame (not shown) provided to the apparatus main body  100 . In this case, it is widely recognized that rigidity of the sheet feeding unit has much to do with a sheet feeding performance and image quality. 
   For example, in a sheet feeding and separating operation, when the sheet feeding unit receives a reaction force from the separating units  107  and  111  through the sheet feeding rollers  106  and  110  and is deformed by the reaction force, a failure in sheet feeding or skew feeding of sheets is caused. As a result, deterioration in image quality or the like is caused. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above problems, and therefore has an object to provide a sheet feeding apparatus and an image forming apparatus which are capable of reducing a height of an apparatus main body and securing an image quality. 
   It is an object of the present invention to provide a sheet feeding apparatus including: a first sheet containing device and a second sheet containing device which are detachably mountable to an apparatus main body and said second sheet containing device is located below said first sheet containing device; a first sheet feeding unit and a second sheet feeding unit capable to feed sheets stacked on said first sheet containing device and said second sheet containing device, respectively; a first holding device and a second holding device capable to hold said first sheet containing device and said second sheet containing device, respectively, slidably in a direction orthogonal to a sheet feeding direction; and wherein said second sheet feeding unit is arranged lateral to said first holding device of said first sheet containing device so that said second sheet feeding unit is provided to be able to abut against said first holding device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram showing a schematic structure of an image forming apparatus provided with a sheet feeding apparatus according to a first embodiment of the present invention; 
       FIGS. 2A ,  2 B, and  2 C are diagrams for explaining a cassette drawer device provided to the image forming apparatus; 
       FIG. 3  is a perspective view of substantial parts of the sheet feeding apparatus; 
       FIG. 4  is a cross-sectional view of substantial parts of the sheet feeding apparatus; 
       FIG. 5  is a diagram showing a schematic structure of an image forming apparatus provided with a sheet feeding apparatus according to a second embodiment of the present invention; 
       FIG. 6  is a diagram showing a schematic structure of a conventional image forming apparatus; and 
       FIGS. 7A ,  7 B, and  7 C are diagrams for explaining a cassette drawer device of the conventional image forming apparatus. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, best modes for implementing the present invention will be described with reference to the accompanying drawings. 
     FIG. 1  shows a schematic structure of an image forming apparatus provided with a sheet feeding apparatus according to a first embodiment of the present invention. 
   In  FIG. 1 , an image forming apparatus main body (hereinafter referred to as “apparatus main body”)  1  includes an image forming portion  1 A for forming an image by an electrophotographic process and a sheet feeding apparatus  1 B for feeding a sheet S to the image forming portion  1 A. 
   The image forming portion  1 A includes a photosensitive drum  2  on which a toner image is formed and a transfer roller  3  for transferring the toner image formed on the photosensitive drum  2  onto the sheet S. In the image forming portion  1 A thus structured, when an image forming operation is started, light corresponding to an image signal is first applied to the photosensitive drum  2  by a laser scanner  4 . By thus applying light corresponding to the image signal, a latent image is formed on the photosensitive drum  2 . Then, the latent image is developed by a toner contained in a process cartridge  5 , thereby forming a toner image (visible image) on the photosensitive drum  2 . 
   Further, the sheet feeding apparatus  1 B includes a sheet feeding cassette  6  serving as a first sheet containing device and a sheet feeding cassette  7  serving as a second sheet containing device, which are a plurality of (two in this embodiment) sheet feeding devices detachably mounted to the apparatus main body  1  one above another with an overlap in a vertical direction. The sheet feeding apparatus  1 B further includes a sheet feeding roller  18  serving as a first sheet feeding device and a sheet feeding roller  22  serving as a second sheet feeding device, for feeding the sheets S stored in sheet feeding cassettes  6  and  7 . The sheet feeding rollers  18  and  22  are driven by a driving transmission apparatus to be rotated simultaneously with the above-mentioned toner image forming operation, thereby feeding the sheet S from the sheet feeding cassettes  6  and  7 . 
   The sheets S fed from the sheet feeding cassettes  6  and  7  are fed into separating units  19  and  23  serving as separating devices which are provided to the sheet feeding cassettes  6  and  7  and which include separating pads  19   a  and  23   a  for separating sheets one from another by press-contacting the sheets with the sheet feeding rollers  18  and  22 . In each of the separating units  19  and  23 , one of the sheets S is separated from another. After that, the separated sheet is conveyed to a transferring part constituted of the photosensitive drum  2  and the transfer roller  3  in synchronism with the image formed on the photosensitive drum  2  by a conveying roller  8  and a registration roller  9 . Then, in the transferring part, a bias is applied to the transfer roller  3 , thereby transferring a toner image onto the sheet S. 
   It should be noted that the sheet S onto which the toner image is thus transferred is then conveyed to a fixing means  10 . The conveyed sheet S is pressurized and heated in the fixing means  10 , thereby fixing the toner image. After that, the sheet S is delivered to a delivery part  12 , which is an upper part of the apparatus, by a delivery roller  11 . 
   In this case, the upper and lower sheet feeding cassettes  6  and  7  each are detachably mounted to the apparatus main body  1 , in other words, a sheet feeding apparatus main body (not shown), through the intermediation of drawer means  20  ( 20 R and  20 L) serving as a first holding device for slidably holding the sheet feeding cassette  6  in a width direction, and a drawer device  24  ( 24 R and  24 L) serving as a second holding device for slidably holding the sheet feeding cassette  7  in the width direction. The cassette drawer devices  20  and  24  have such structures as shown in  FIGS. 2A ,  2 B, and  2 C. 
     FIG. 2A  is a front view showing the cassette drawer device  20 ,  24  viewed from a direction toward which the cassette is drawn out therefrom.  FIGS. 2B and 2C  are perspective views showing a state in which a sheet feeding cassette  6 ,  7  is mounted in the cassette drawer device  20 ,  24  and a state in which the sheet feeding cassette  6 ,  7  is drawn out from the cassette drawer device  20 ,  24 , respectively. 
   As shown in  FIGS. 2A to 2C , the cassette drawer device  20 ,  24  is arranged outside the sheet feeding cassette  6 ,  7 , and includes a base-member  20   a ,  24   a  that is fixed on a front-and-rear side plate  1   a ,  1   b  (refer to  FIG. 1 ) and a slide member  20   b ,  24   b  that is slidably held in the base member  20   a ,  24   a . The sheet feeding cassette  6 ,  7  is mounted to the slide member  20   b ,  24   b , thereby being detachably mounted into the apparatus main body  1  through the intermediation of the cassette drawer device  20 ,  24 . The base member  20   a ,  24   a  is formed to have a C-shape cross section, and when mounting the sheet feeding cassettes  6  and  7 , the slide members  20   b  and  24   b  slidably contact with inner sides thereof, so the cassette drawer devices  20  and  24  have a high rigidity as a whole. 
   In this embodiment, as shown in  FIGS. 1 and 2A , the cassette drawer devices  20  and  24  are arranged below the separating units  19  and  23  of the sheet feeding cassettes  6  and  7 , respectively, and at the same time, are arranged on the same surfaces as bottom surfaces of the sheet feeding cassettes  6  and  7  or above the bottom surfaces of the sheet feeding cassettes  6  and  7 , respectively. By thus arranging the cassette drawer devices  20  and  24 , it is possible to shorten the length of the apparatus main body  1  in the sheet feeding direction. 
   Further, in this embodiment, the sheet feeding roller  22  for the lower sheet feeding cassette  7  serving as a sheet containing device located at a lower part of the sheet feeding apparatus is protruded above the bottom surface of the upper sheet feeding cassette  6  serving as a sheet containing device which is immediately above the sheet feeding cassette  7 , and at the same time, the sheet feeding roller  22  is arranged beside the drawer device  20  for the upper sheet feeding cassette  6  as shown in  FIG. 3 . In  FIG. 3 , a sheet feeding unit  29  includes the sheet feeding roller  22  for the lower sheet feeding cassette  7 , and a sheet feeding unit  34  includes the sheet feeding roller  18  for the upper sheet feeding cassette  6 . 
   As described above, the-sheet feeding roller  22  for the lower sheet feeding cassette  7  is arranged beside the drawer device  20  for the upper sheet feeding cassette  6  to be protruded above the bottom surface of the upper sheet feeding cassette  6 , to thereby make it possible to cause the upper sheet feeding cassette  6  to overlap with the sheet feeding roller  22  for the lower sheet feeding cassette  7  in the height direction. Thus, the height of the apparatus main body  1  can be reduced by the overlapping amount. 
   It should be noted that the partition plate  113  interposed between the cassettes (refer to  FIG. 6 ) is removed, or an opening portion in which the sheet feeding roller  22  can be arranged is provided to the partition plate  113  so that the sheet feeding roller  22  for the lower sheet feeding cassette  7  can be arranged beside the drawer device  20  for the upper sheet feeding roller  6  to be protruded above the bottom surface of the upper sheet feeding cassette  6 . 
   On the other hand, the sheet feeding units  29  and  34  which include the sheet feeding rollers  18  and  22  receive a reaction force from the separating units  19  and  23  through the sheet feeding rollers  18  and  22 , respectively, for example, in the sheet feeding and separating operation. 
   When the sheet feeding units  29  and  34  receive such the reaction force, the sheet feeding unit  34  of the upper cassette  6  can be firmly fixed to, for example, a frame (not shown) of the apparatus main body  1 . On the other hand, as shown in  FIG. 4 , the sheet feeding unit  29  of the lower cassette  7  is sandwiched between the cassette drawer device  20  for the upper cassette  6  and an external unit  28  for forming a sheet transport path R, which makes it difficult for the sheet feeding unit  29  of the lower cassette  7  to be firmly held to the frame or the like. 
   In this embodiment, on sheet feeding, the lower sheet feeding unit  29  is provided with a bumping portion  39  which hits against the cassette drawer device  20  for the upper sheet feeding cassette  6  when the lower sheet feeding unit  29  receives the reaction force from the separating unit  23 . By providing such the bumping portion  39 , in the sheet feeding operation of the lower sheet feeding unit  29 , when the lower sheet feeding unit  29  receives the reaction force indicated by the arrow F from the separating unit  23 , the bumping portion  39  hits (abuts) against the cassette drawer device  20  for the upper sheet feeding cassette  6 . 
   When receiving the reaction force, the lower sheet feeding unit  29  hits against the cassette drawer device  20  which has a high rigidity and is a part of structures of the apparatus main body  1 , thereby making it possible to prevent the sheet feeding unit  29  from being deformed. Thus, skew feeding of the sheet S or the like at the time of sheet feeding can be prevented, thereby enhancing the sheet feeding performance. As a result, the image quality can be secured. It should be noted that the bumping portion  39  might be provided to the cassette drawer device  20  for the upper sheet feeding cassette  6  instead of being provided to the sheet feeding unit  29 . 
   As described above, when the sheet feeding roller  22  for the lower sheet feeding cassette  7  is arranged beside the cassette drawer device  20  for the upper sheet feeding cassette  6  to be protruded above the bottom surface of the upper sheet feeding cassette  6 , and sheet feeding unit  29  of the lower sheet feeding cassette  7  is brought into contact with the cassette drawer device  20  for the upper sheet feeding cassette  6 , the height of the apparatus main body  1  can be reduced, and the deformation of the sheet feeding unit  29  can be prevented, thereby making it possible to secure the image quality. 
   As described above, in the case where the sheet feeding roller  22  for the lower sheet feeding cassette  7  is arranged beside the cassette drawer device  20  for the upper sheet feeding cassette  6  to be protruded above the bottom surface of the upper sheet feeding cassette  6 , there is a space between a back end of the lower sheet feeding cassette  7  in the sheet feeding direction and the apparatus main body  1  as shown in  FIG. 1 . 
   For example, by increasing the length of the lower sheet feeding cassette  7  in the sheet feeding direction, the space formed between the back end of the lower sheet feeding cassette  7  in the sheet feeding direction and the apparatus main body  1  can be effectively utilized. In addition, by increasing the length of the lower sheet feeding cassette  7  as described above, the size of the sheet contained in the sheet feeding cassette  7  can be increased. 
   Next, described as an example of the lower sheet feeding cassette  7  is a second embodiment of the present invention which employs a lower sheet feeding cassette having a length longer in the sheet feeding direction. 
     FIG. 5  shows a schematic structure of an image forming apparatus including a sheet feeding apparatus according to the second embodiment of the present invention. In  FIG. 5 , the identical reference symbols with those of  FIG. 1  indicate the identical or equivalent parts. 
   In  FIG. 5 , a plurality of (two in this embodiment) sheet feeding cassettes  6 A and  7 A serving as a sheet containing device are detachably mounted to the apparatus main body  1  one above another with an overlap in a vertical direction. In this embodiment, the lower sheet feeding cassette  7 A has a length longer in the sheet feeding direction than the upper sheet feeding cassette  6 A. 
   It should be noted that in this embodiment, the lower sheet feeding cassette  7 A can contain sheets with a size ranging, for example, from A 5  (148.5 mm×210 mm) to LDR (279 mm×432 mm), and the upper sheet feeding cassette  6 A can contain sheets with a size ranging, for example, from a minimum size to B 4  (257 mm×364 mm). 
   By thus increasing the length of the lower sheet feeding cassette  7 A, the space formed at the left side of the lower cassette  7 A can be effectively utilized, and at the same time, the number of types of sheets contained in the sheet feeding cassettes  6 A and  7 A can be increased. It should be noted that the case where the two sheet feeding cassettes are employed is described in this embodiment, but the present invention can also be applied to a case where more than two sheet feeding cassettes are provided. 
   This application claims priority from Japanese Patent Application No. 2005-128407 filed on Apr. 26, 2005, which is hereby incorporated by reference.