Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of Korean Patent Application No. 2004-1669, filed on Jan. 9, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety and by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present general inventive concept relates to a paper feeding cassette of an image forming apparatus which stacks sheets of paper and can be attached or detached to or from a main body. 
   2. Description of the Related Art 
   In general, an image forming apparatus, such as a printer, a copier, or a multifunctional device, includes a paper feeding cassette which stacks a sheet of paper inside of the paper feeding cassette and is attached or detached to or from a main body. A paper stacking plate is installed inside the paper feeding cassette to lift the sheet of paper that is stacked on the paper stacking plate. Thus, the paper stacking plate allows the sheet of paper to contact a pickup roller installed in the main body, and the sheet of paper is picked up and transferred to an inside of the main body when the pickup roller is rotated. 
   A method of lifting the paper stacking plate in the paper feeding cassette is performed in two ways. First, the paper stacking plate is elastically biased in an upward direction by an elastic force of an elastic unit, such as a spring installed under the paper stacking plate. When a plurality of sheets of paper is stacked on the paper stacking plate, the paper stacking plate is lifted by the weight of the paper. This method is generally used in a case where an amount of the paper stacked on the paper feeding cassette is small. Second, when the amount of the paper stacked on the paper feeding cassette is large, like in a large copier, the weight of the paper cannot be supported using the elastic force of the elastic unit such as the spring. Thus, an additional device to lift the paper stacking plate is needed. In this method, an additional lift plate connected to a driving motor is used so that the lift plate is ascended and descended under the paper stacking plate. 
   U.S. Pat. No. 5,100,122 discloses an invention having the above structure. That is, a knock-up plate to stack paper in a feed cassette is installed, and a lift plate is installed under the knock-up plate while being fixed in a rotating pivot. A gear is installed at one side of the rotating pivot and is engaged with a gear installed in a lift plate driving motor. 
   The rotating pivot is rotated by a rotating force of the lift plate driving motor. The knock-up plate is lifted when the rotating pivot is rotated together with the lift plate. Then, the paper contacts a pickup roller installed above the paper feeding cassette. In this case, a sensor senses whether the paper is in contact with the pickup roller and allows the operation of the lift plate driving motor to stop when the paper contacts the pickup roller. 
   A frictional force by which the paper is picked up using the pickup roller is generated by a force by which the lift plate, based on the rotation of the lift plate driving motor, lifts the paper stacking plate. 
   However, when a controller does not control the lift plate driving motor, and the lift plate driving motor operates continuously although the sensor senses that the paper has contacted the pickup roller, the knock-up plate lifts continuously, and the paper is excessively pressed against the pickup roller. Furthermore, an operation of detaching the paper feeding cassette from the main body may not be performed smoothly. 
   SUMMARY OF THE INVENTION 
   The present general inventive concept provides a paper feeding cassette which descends a paper stacking plate compulsively to detach paper from a pickup roller when paper is excessively pressed by the pickup roller. 
   Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
   The foregoing and/or other aspects and advantages of the present general inventive concept are achieved by providing a paper feeing cassette of an image forming apparatus, the paper feeding cassette comprising a paper stacking plate to stack sheets of paper thereon; a lift unit placed under the paper stacking plate to ascend the paper stacking plate having a rotating pivot, a driving motor to rotate the rotating pivot, and a connection portion to connect the rotating pivot to the driving motor; and a release unit to separate the connection portion from the rotating pivot, to disconnect the driving motor from the rotating pivot, to cause the paper stacking plate to descend by its weight, and to separate the sheets of paper from a pickup roller. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a perspective view illustrating a paper feeding cassette having a release unit according to an embodiment of the present general inventive concept; 
       FIG. 2  is a perspective view illustrating the release unit of the paper feeding cassette of  FIG. 1 ; 
       FIGS. 3 and 4  are plan views illustrating an operation of the release unit of the paper feeding cassette of  FIG. 1 ; 
       FIG. 5  is a cross-sectional view illustrating an operation of feeding a sheet of paper from the paper feeding cassette of  FIG. 1 ; 
       FIG. 6  is a perspective view illustrating a paper feeding cassette having a release unit according to another embodiment of the present general inventive concept; 
       FIG. 7  is a perspective view illustrating the release unit of the paper feeding cassette of  FIG. 6 ; and 
       FIGS. 8 and 9  are plan views illustrating the operation of the release unit of the paper feeding cassette of  FIG. 6 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. 
     FIG. 1  is a perspective view illustrating a paper feeding cassette having a release unit according to an embodiment of the present general inventive concept.  FIG. 2  is a perspective view illustrating the release unit of the paper feeding cassette of  FIG. 1 .  FIG. 5  is a cross-sectional view illustrating the operation of feeding a sheet of paper from the paper feeding cassette of  FIG. 1 . 
   Referring to  FIGS. 1 ,  2 , and  5 , a paper feeding cassette  100  may include a cassette main body  110 , a paper stacking plate  111 , a lift unit  120 , and a release unit  130 . The paper stacking plate  111  can be installed in the cassette main body  110  to rotate in upward and downward directions, and sheets of paper S are stacked on the paper stacking plate  111 . The lift unit  120  can be placed under the paper stacking plate  111  and causes the sheets of paper S stacked on the paper stacking plate  111  to contact a pickup roller  200  or to separate from the pickup roller  200  by ascending or descending the paper stacking plate  111 , respectively. The release unit  130  applies a physical force to the lift unit  120  to compulsively descend the paper stacking plate  111  and to remove a force applied to the pickup roller when the sheets of paper S stacked on the paper stacking plate  111  are excessively pressed toward the pickup roller by a force generated by the lift unit  120 . 
   One side of the paper stacking plate  111  can be installed in the cassette main body  110  to rotate in upward and downward directions by a pivot  112  ( FIG. 5 ), and the sheets of paper S can be stacked on the paper stacking plate  111 . The paper stacking plate  111  can descend toward a cassette bottom  115  by its weight with the sheets of paper S stacked thereon. 
   The lift unit  120  may include a rotating pivot  121 , a lift lever  123 , a protrusion  128 , and a connection portion  127 . The rotating pivot  121  can be supported by the cassette main body  110  to rotate and can have a plurality of protruding pins  122  opposite to each other at one side. One side of the lift lever  123  can be fixed on the rotating pivot  121 , and the other side thereof can contact the paper stacking plate  111 . The lift lever  123  can be rotated together with the rotating pivot  121  to cause the paper stacking plate  111  to ascend or descend. The protrusion  128  can be installed to be slid in a direction of a driving pivot  125  of a driving motor  124  installed in a main body of a printer (not shown), be elastically biased in a direction of the rotating pivot  121  by a spring  126 , and contact a release portion  1313  that will be described later. The connection portion  127  can have a plurality of cutting parts  129  into which the pins  122  can be inserted to be attached thereto or detached therefrom. 
   The connection portion  127  is not limited to the above description, and various modifications of the connection portion  127  may be possible so that the connection portion  127  can connect or disconnect a power of the driving motor  124  to or from the rotating pivot  121 . 
   The release unit  130  may include a release lever  131 , an opening lever  133 , and a connection lever  132 . The release lever  131  can be supported by a cassette rear plate  114  to rotate and disconnect the connection portion  127  from the rotating pivot  121 . The opening lever  133  can be supported by a cassette front plate  113  to rotate. The connection lever  132  connects the opening lever  133  to the release lever  131  and allows the release lever  131  to pivot when the opening lever  133  is pivoted. 
   The release lever  131  may include a body  1311 , rotating portions  1312 , the release portion  1313 , and an interlocking portion  1314 . The rotating portions  1312  can protrude from both sides of the body  1311  to support the body  1311  and to rotate on the cassette rear plate  114  of the cassette main body  110 . The release portion  1313  surrounds the connection portion  127  and contacts the protrusion  128  to force the connection portion  127  of the lift unit  120  to disconnect from the rotating pivot  121 . The interlocking portion  1314  is connected to the connection lever  132  and interlocks with the connection lever  132 . 
   The release lever  131  may be installed at an external side of the cassette main body  110  to rotate on the cassette rear plate  114 . 
   The opening lever  133  may include a pressing portion  1331 , a main frame  1332 , support portions  1333 , an elastic portion  1334 , and a connection portion  1335 . The main frame  1332  can include the pressing portion  1331  to which a force can be applied. The support portions  1333  can protrude from both sides of the main frame  1332  to support the main frame  1332  and to rotate on the cassette front plate  113  of the cassette main body  110 . The elastic portion  1334  can surround each of the support portions  1333 . One end of the elastic portion  1334  can be fixed at a stopping portion  1336  installed in the main frame  1332 , and the other end thereof can be fixed at the cassette front plate  113 . The elastic portion  1334  applies an elastic force to the main frame  1332 . A connection portion  1335  connects the main frame  1332  to the connection lever  132 . 
   When a user pulls the opening lever  133  by hand, a force is applied to the pressing portion  1331 , and the opening lever  133  is rotated around the supporting portion  1333 . When a force applied to the opening lever  133  is removed, the opening lever  133  is returned to its original location by the elastic portion  1334 . 
   The connection lever  132  may include a through hole  1321  and an interference portion  1322 . The through hole  1321  can be formed at one end of the connection lever  132  so that the connection portion  1335  of the opening lever  133  is inserted into the through hole  1321  and the opening lever  133  is connected to the connection lever  132 . The interference portion  1322  can be formed at another end of the connection lever  132  in contact with the interlocking portion  1314  of the release lever  131  to interfere with the release lever  131 . 
   The connection lever  132  may be installed in the cassette bottom  115  to slide in a direction of an arrow A (see  FIG. 1 ). The interference portion  1322  may be installed outside of the cassette main body  110  and contact the interlocking portion  1314  to rotate the release lever  131 . 
   Referring to  FIG. 1 , a first sensor  220  to sense whether the paper feeding cassette  110  is inserted into a main body (not shown), and a second sensor  210  to sense whether the sheets of paper S stacked on the paper stacking plate  111  are in contact with the pickup roller  200 , may be installed in the cassette rear plate  114  or the main body of the printer (not shown). 
   The operation of the release unit  130  having the above described structure will be described in more detail while referring to  FIGS. 1-5 . 
     FIGS. 3 and 4  are plan views illustrating the operation of the release unit  130  of the paper feeding cassette of  FIG. 1 . Referring to  FIGS. 1 ,  2 ,  3 , and  5 , when the paper feeding cassette  110  is inserted into the main body of the printer (not shown), the protruding pins  122  of the rotating pivot  121  are inserted into the cutting parts  129  and engage with the cutting parts  129 . When the driving motor  124  is rotated, a rotating force is applied to the rotating pivot  121  by the connection portion  127 , and the rotating pivot  121  is rotated. Then, the lift lever  123  lifts the paper stacking plate  111 , and the sheets of paper S contact the pickup roller  200 . 
   When the driving motor  124  is not properly controlled and the lift lever  123  excessively pushes the paper stacking plate  111  toward the pickup roller  200 , it is difficult to pickup the sheets of paper S using the pickup roller  200 , and it is difficult to detach the paper feeding cassette  100  from the main body of the printer (not shown). 
   In this case, as shown in  FIGS. 1 and 4 , when the user pulls the opening lever  133  toward the cassette front plate  113 , the connection lever  132  is slid in a direction of the arrow A (see  FIG. 1 ), and the interference portion  1322  pulls the interlocking portion  1314 . Thus, the release lever  131  is rotated around the rotating portions  1312 , and the release portion  1313  pushes the protrusion  128  toward the driving motor  124 . 
   Then, the connection portion  127  is slid toward the driving motor  124  in a direction of the driving pivot  125 , and the protruding pins  122  are detached from the cutting parts  129  so that the connection portion  127  and the rotating pivot  121  are separated from each other. 
   When the rotating pivot  121  is separated from the connection portion  127 , the paper stacking plate  111  is rotated toward the cassette bottom  115  by a weight of its load. Thus, the sheets of paper S are separated from the pickup roller  200 . As a result, the paper feeding cassette  100  may be easily detached from the main body of the printer (not shown). 
   When the user removes force from the opening lever  133 , the connection portion  127  is returned to its original location by an elastic force of the spring  126 , and the release lever  131  is returned to its original location. The opening lever  133  is returned to its original location by the elastic force of the elastic portion  1334 . 
     FIG. 6  is a perspective view illustrating a paper feeding cassette having a release unit according to another embodiment of the present general inventive concept.  FIG. 7  is a perspective view illustrating the release unit of the paper feeding cassette of  FIG. 6 .  FIGS. 8 and 9  are plan views illustrating the operation of the release unit according of the paper feeding cassette of  FIG. 6 . 
   Referring to  FIGS. 6 through 9 , in a paper feeding cassette  300  of  FIG. 6 , the paper stacking plate  111  and the lift unit  120  are the same as those of the paper feeding cassette  100  of  FIG. 1 . The only difference between the paper feeding cassette  110  of  FIG. 1  and the paper feeding cassette  300  of  FIG. 6  is in a connection lever  332  and a release lever  331  of a release unit  330 . The same reference numerals as those of  FIGS. 1 through 4  represent the same elements having the same functions, and thus detailed descriptions thereof will be omitted. 
   The release lever  331  may include a body  3311 , rotating portions  3312 , a release portion  3313 , and an interlocking portion  3314 . The rotating portions  3312  may protrude from both sides of the body  3311  to support the body  3311  and to rotate on the cassette rear plate  114  of the cassette main body  110 . The release portion  3313  surrounds the connection portion  127  and contacts the protrusion  128  to force the connection portion  127  of the lift unit  120  to disconnect from the rotating pivot  121 . The interlocking portion  3314  can be connected to the connection lever  332  and can interlock with the connection lever  332 . The release lever  331  may be installed at an external side of the cassette main body  110  to rotate on the cassette rear plate  114 . 
   The connection lever  332  may include through holes  3321  formed at both sides the connection lever  332  so that the connection portion  1335  of the opening lever  133  and the interlocking portion  3314  of the release lever  331  can be inserted into the respective through holes  3321  to connect the opening lever  133  to the release lever  331 . 
   When the user pulls the opening lever  133  toward the cassette front plate  113 , the connection lever  332  is slid in a direction of an arrow B and pulls the interlocking portion  3314 . Thus, the release lever  331  is rotated around the rotating portions  3312 , and the release portion  3313  pushes the protrusion  128  toward the driving motor  124 . 
   Then, the connection portion  127  is slid toward the driving motor  124  in a direction of the driving pivot  125  (see  FIG. 8 ), and the protruding pins  122  are detached from the cutting parts  129  so that the connection portion  127  and the rotating pivot  121  are separated from each other. 
   As described above, the paper feeding cassettes according to the various embodiments of the present general inventive concept have the following effects. First, when sheets of paper are stacked on a paper feeding plate and any of the sheets of paper is excessively pressed by a pickup roller during a printing operation, the paper feeding cassette can be detached from a main body without damage or deformation of any parts thereof. Second, when the paper feeding cassette is detached from the main body, the paper stacking plate falls first such that the sheets of paper are prevented from being twisted by the pickup roller. 
   Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.

Technology Category: b