Patent Publication Number: US-6661984-B2

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus of the type having a sheet storing unit accommodating a sheet tray, which is movable between an operative position and an inoperative position, and an image forming unit removably mounted on the top of the sheet storing unit when in use. 
     2. Description of the Background Art 
     An image forming apparatus of the type described is known in the art and made up of a sheet storing unit and an image forming unit removably mounted on the top of the sheet storing unit when in use. The sheet storing unit includes a sheet tray loaded with sheet rolls. A sheet selectively paid out from either one of the sheet rolls is fed to the image forming unit. The sheet tray is selectively slidable into the sheet storing unit to an operative position or out of the sheet storing unit to an inoperative position in substantially the horizontal direction. 
     The conventional image forming apparatus of the type described has the following problem unsolved. When the image forming apparatus is newly purchased and installed at the user&#39;s station or when it is moved to another place, the image forming unit is absent on the sheet storing unit. Assume that in such a condition a person pulls out the sheet tray loaded with the sheet rolls or loads the sheet rolls in the sheet tray pulled out. Then, a heavy moment of rotation ascribable to the sheet tray acts on the sheet storing unit and is apt to cause the sheet storing unit to falldown. 
     Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication No. 6-242641. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an image forming apparatus capable of preventing a sheet storing unit thereof from falling down in the absence of an image forming unit due to a moment generated when a person pulls out a sheet tray loaded with sheets or replenishes sheets to the sheet tray pulled out. 
     An image forming apparatus of the present invention is generally made up of a sheet storing unit and an image forming unit removably mounted on the top of the sheet storing unit when in use. The sheet storing unit accommodates a sheet tray loaded with sheets and selectively movable into the sheet storing unit to an operative position or out of the same to an inoperative position. A locking mechanism inhibits the sheet tray from being moved to the inoperative position. An unlocking device unlocks the locking mechanism when the image forming unit is mounted to the sheet storing unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which: 
     FIG. 1 is a front view showing a conventional image forming apparatus in a usable condition; 
     FIG. 2 is a front view showing a sheet storing unit included in the apparatus of FIG. 1 in a condition wherein a sheet tray is pulled out of the sheet storing unit; 
     FIG. 3 is a front view showing an image forming apparatus embodying the present invention; 
     FIG. 4 is a front view showing a sheet storing unit included in the illustrative embodiment; 
     FIG. 5 is an isometric view showing a leaf spring forming part of a locking mechanism included in the illustrative embodiment; 
     FIG. 6 is a front view showing an alternative embodiment of the present invention; and 
     FIG. 7 is a front view showing another alternative embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     To better understand the present invention, brief reference will be made to a conventional image forming apparatus, shown in FIG.  1 . As shown, the image forming apparatus is generally made up of a sheet storing unit  1  and an image forming unit  2  removably mounted on the top of the sheet storing unit  1  when in use. The sheet storing unit  1  includes a sheet tray  4  loaded with sheet rolls  3 . A sheet selectively paid out from the sheet rolls  3  is fed to the image forming unit  2 . The sheet tray  4  is selectively slidable into the sheet storing unit  1  to an operative position or out of the sheet storing unit  1  to an inoperative position in substantially the horizontal direction. The operative position and inoperative position are respectively indicated by a solid line and a dash-and-dots line in FIG. 1; the inoperative position is indicated by a solid line in FIG.  2 . 
     As for weight, the image forming unit  2  is heavy because it accommodates an image forming mechanism including a photoconductive element and a heat roller. By contrast, the sheet storing unit  1  is a simple casing having a space in which the sheet tray  4  is disposed, and is therefore light. The sheet tray  4  is also light, but becomes heavy when loaded with the sheet rolls  3 . As shown in FIG. 1, when the image forming unit  2  is mounted on the sheet storing unit  1  when in use, the weight of the heavy image forming unit  2  acts on the sheet storing unit  1  vertically downward. Therefore, when the sheet tray  4  loaded with the sheet rolls  3  is pulled out to the inoperative position or when the sheet rolls  3  are replenished to the sheet tray  4  pulled out, the image forming unit  2  does not fall down despite a heavy moment of rotation acting thereon due to the sheet tray  4  and remains stable on the sheet feeding unit  1 . 
     On the other hand, when the image forming apparatus is newly purchased and installed at the user&#39;s station or when it is moved to another place, the image forming unit  2  is absent on the sheet storing unit  1 . Assume that in such a condition a person pulls out the sheet tray  4  loaded with the sheet rolls  3  or loads the sheet rolls  3  in the sheet tray  4  pulled out. Then, a heavy moment of rotation ascribable to the sheet tray  4  acts on the sheet storing unit  1  and is apt to cause the sheet storing unit  1  to fall down in a direction indicated by an arrow a in FIG.  2 . To solve this problem, the leg portion of the sheet storing unit  1  may be extended outward in the direction in which the sheet tray  4  is slidable, as indicated by a dash-and-dots line in FIG.  2 . However, the extended leg portion increases the floor area to be occupied by the image forming apparatus and is likely to trip up the operator&#39;s foot. 
     Referring to FIGS. 3 through 5, an image forming apparatus embodying the present invention is shown and generally made up of a sheet storing unit  11  and an image forming unit  12  removably mounted on the top of the sheet storing unit  11  when in use. The image forming unit  12  is so sized as to be capable of forming images on sheets of relatively large sizes including sizes A 0  and A 1 . 
     Again, the image forming unit  12  accommodates an image forming mechanism including a photoconductive element and a heat roller and is therefore heavy. The sheet storing unit  11  includes a sheet tray  14  loaded with sheet rolls  13 . A sheet selectively paid out from the sheet rolls  13  is fed to the image forming unit  12 . The sheet tray  14  is selectively slidable into the sheet storing unit  11  to an operative position or out of the sheet storing unit  11  to an inoperative position in substantially the horizontal direction. The operative position and inoperative position are respectively indicated by solid lines in FIGS. 3 and 4 and a dash-and-dots line in FIG.  3 . The sheet storing unit  11  is a simple casing having a space in which the sheet tray  14  is disposed, and is therefore light. The sheet tray  14  is also light, but becomes heavy when loaded with the sheet rolls  13 . 
     A locking mechanism  15  is arranged in the upper portion of the sheet storing unit  11  for locking the sheet tray  14  at the operative position to thereby prevent it from being slid to the inoperative position. The locking mechanism  15  is implemented by a projection or first engaging portion  16  and a leaf spring or locking member  17 . The projection  16  is affixed to the top wall of the sheet storing unit  11  and extends downward. The leaf spring  17  is affixed to the sheet tray  4  and formed with a hole or second engaging portion  18  configured to mate with the projection  16 . The leaf spring  17  is resiliently deformable between a locking position where it mates with the projection  16  and an unlocking position where it is released from the projection  16 . The leaf spring  17  is constantly biased toward the locking position. 
     A plurality of legs protrude downward from the bottom of the image forming unit  12 . One of the legs, labeled  19 , plays the role of a pressing member or unlocking member for unlocking the locking mechanism  15 . More specifically, when the image forming unit  12  is mounted to the sheet storing unit  11 , the leg  19  presses the leaf spring  17  downward to the unlocking position. 
     In FIG. 3, the image forming apparatus is shown in a condition for use, as indicated by solid lines. In this condition, the image forming unit  12  is mounted on the top of the sheet storing unit  11  and ready to receive the sheet  13  from the sheet feeding unit  11  for forming an image. The leaf spring  17  is pressed downward by the leg  19  out of engagement with the projection  16 . The sheet tray  14  can therefore freely slide from the operative position to the inoperative position without being restricted by the locking mechanism  15 . The sheet tray  14  will be pulled out to the inoperative position when the roll sheets  13  should be replaced with roll sheets of different sizes, when the sheet rolls  13  should be replenished or when the sheet tray  14  should be maintained in the event of, e.g., a sheet jam. 
     So long as the image forming unit  12  is mounted on the sheet storing unit  11  for use, the weight of the heavy image forming unit  12  acts on the sheet storing unit  11  vertically downward. Therefore, when the sheet tray  14  loaded with the sheet rolls  13  is pulled out to the inoperative position or when the sheet rolls  13  are replenished to the sheet tray  14  so pulled out, the image forming unit  12  does not fall down despite a heavy moment of rotation acting thereon due to the sheet tray  14  and remains stable on the sheet feeding unit  11 . 
     Assume that the image forming unit  12  is removed from the top of the sheet storing unit  11  when the image forming apparatus is newly purchased and installed at the user&#39;s station or when it is moved to another place. Then, as shown in FIG. 4, the leaf spring  17  resiliently deforms upward to the locking position where the hole  18  mates with the projection  16  due to the absence of the leg  19 , thereby locking the locking mechanism  15 . In this condition, the sheet tray  14  is inhibited from sliding out of the sheet feeding unit  11  and maintained in the operative position. More specifically, when the image forming unit  12  is absent on the sheet storing unit  11 , the locking mechanism  15  inhibits a person from pulling the sheet tray  14  out of the sheet storing unit  11 . This successfully obviates a moment that would cause the sheet storing unit  11  to fall down due to the displacement of the center of gravity. 
     Further, the illustrative embodiment does not need the extension of the leg portion described in relation to the conventional image forming apparatus and therefore saves space and obviates the previously stated accident. 
     The hole  18  of the leaf spring  17  and the projection  16  may be replaced with each other, if desired. Further, the projection  16  and leaf spring  17  may alternatively be affixed to the sheet tray  14  and sheet storing unit  11 , respectively. Moreover, the leaf spring  17  may be removably mounted to the sheet tray  14 , i.e., it may be detached after the image forming unit  12  has been mounted to the sheet storing unit  11  and attached before the former is dismounted from the latter. In addition, the sheet rolls  13  loaded on the sheet tray  14  may, of course, be replaced with cut sheets of a preselected size. 
     An alternative embodiment of the present invention will be described with reference to FIG.  6 . In FIG. 6, structural elements identical with those shown in FIGS. 2 through 5 are designated by identical reference numerals and will not be described specifically in order to avoid redundancy. As shown, the image forming apparatus is generally made up of a sheet storing unit  11   a  and the image forming unit  12  removably mounted on the sheet storing unit  11   a  when in use. Again, the image forming unit  12  is so sized as to be capable of forming images on sheets of relatively large sizes including sizes A 0  and A 1 . 
     The sheet storing unit  11   a  includes a sheet tray  14   a  loaded with a sheet roll  13 . In the illustrative embodiment, the sheet tray  14   a  is angularly movable about a shaft  20   a  extending in the horizontal direction. The sheet tray  14   a  is selectively movable about the shaft  20   a  into the sheet storing unit  11   a  to an operative position or out of the sheet storing unit  11   a  to an inoperative position. The operative position and inoperative position are respectively indicated by a solid line and a dash-and-dots line in FIG.  6 . The shaft  20   a  is positioned above the sheet tray  14   a.    
     The sheet storing unit  11   a  is a simple casing having a space in which the sheet tray  14   a  is disposed, and is therefore light. The sheet tray  14   a  is also light, but becomes heavy when loaded with the sheet rolls  13 . 
     A locking mechanism  15   a  is arranged in the upper portion of the sheet storing unit  11   a  for locking the sheet tray  14   a  at the operative position to thereby prevent it from being slid to the inoperative position. The locking mechanism  15   a  is implemented by a projection or first engaging portion  16   a  and a leaf spring or locking member  17   a . The projection  16   a  protrudes obliquely downward from the sheet tray  14   a . The leaf spring or locking member  17   a  is affixed to the sheet storing unit  11   a  and formed with a hole or second engaging portion  18   a  configured to mate with the projection  16   a . The leaf spring  17   a  is resiliently deformable between a locking position where it mates with the projection  16   a  and an unlocking position where it is released from the projection  16   a . The leaf spring  17   a  is constantly biased toward the locking position. 
     In FIG. 6, the image forming apparatus is shown in a condition for use, as indicated by solid lines. In this condition, the image forming unit  12  is mounted on the top of the sheet storing unit  11   a  and ready to receive the sheet  13  from the sheet feeding unit  11   a  for forming an image. The leaf spring  17   a  is pressed downward by the leg  19  of the image forming unit  12  out of engagement with the projection  16   a . The sheet tray  14   a  can therefore freely move about the shaft  20   a  out of the sheet feeding unit  11   a  without being restricted by the locking mechanism  15   a.    
     So long as the image forming unit  12  is mounted on the sheet storing unit  11   a  for use, the weight of the heavy image forming unit  12  acts on the sheet storing unit  11   a  vertically downward. Therefore, when the sheet tray  14   a  loaded with the sheet roll  13  is pulled out to the inoperative position or when the sheet roll  13  is replenished to the sheet tray  14   a  pulled out, the image forming unit  12  does not fall down despite a heavy moment of rotation acting thereon due to the sheet tray  14   a  and remains stable on the sheet feeding unit  11   a.    
     Assume that the image forming unit  12  is removed from the top of the sheet storing unit  11   a  when the image forming apparatus is newly purchased and installed at the user&#39;s station or when it is moved to another place. Then, the leaf spring  17   a  resiliently deforms upward to the locking position where the hole  18   a  mates with the projection  16   a due to the absence of the leg  19 , thereby locking the locking mechanism  15   a . In this condition, the sheet tray  14   a  is inhibited from sliding out of the sheet feeding unit  11   a  and maintained in the operative position. More specifically, when the image forming unit  12  is absent on the sheet storing unit  11   a , the locking mechanism  15   a  inhibits a person from pulling the sheet tray  14   a  out of the sheet storing unit  11   a . This successfully obviates a moment that would cause the sheet storing unit  11   a  to fall down due to the displacement of the center of gravity. 
     Further, the illustrative embodiment, like the previous embodiment, does not need the extension of the leg portion described in relation to the conventional image forming apparatus and therefore saves space and obviates the previously stated accident. 
     FIG. 7 shows another alternative embodiment of the present invention. As shown, the image forming apparatus is generally made up of a sheet storing unit  11   b  and the image forming unit  12  removably mounted on the sheet storing unit  11   b  when in use. Again, the image forming unit  12  is so sized as to be capable of forming images on sheets of relatively large sizes including sizes A 0  and A 1 . 
     The sheet storing unit  11   b  includes a sheet tray  14   b  loaded with the sheet roll  13 . In the illustrative embodiment, the sheet tray  14   b  is angularly movable about a shaft  20   b  extending in the horizontal direction. The sheet tray  14   b  is selectively movable about the shaft  20   b  into the sheet storing unit  11   b  to an operative position or out of the sheet storing unit  11   b  to an inoperative position. The operative position and inoperative position are respectively indicated by a solid line and a dash-and-dots line in FIG.  7 . The shaft  20   b  is positioned above the sheet tray  14   b.    
     The sheet storing unit  11   b  is a simple casing having a space in which the sheet tray  14   b  is disposed, and is therefore light. The sheet tray  14   b  is also light, but becomes heavy when loaded with the sheet rolls  13 . 
     The illustrative embodiment also includes the locking mechanism  15  arranged in the upper portion of the sheet storing unit  11   b . The locking mechanism  15  is identical in configuration and operation with the locking mechanism  15  described with reference to FIGS. 3 through 5 and will not be described specifically in order to avoid redundancy. 
     In summary, in accordance with the present invention, an image forming apparatus is made up of a sheet storing unit and an image forming unit removably mounted on the sheet storing unit when in use. When the image forming unit is removed from the sheet storing unit, the sheet storing unit is prevented from falling down due to a moment ascribable to the pull-out of a sheet tray. This can be done with a simple locking mechanism, a first and a second engaging portion simple in configuration, simple unlocking means without resorting to an exclusive pressing member, which would increase the cost of the apparatus. 
     Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.