Patent Publication Number: US-2009224460-A1

Title: Sheet feeding device and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus such as a copying machine, a facsimile device, a printer and the like, and also relates to a sheet feeding device arranged in the image forming apparatus for feeding a sheet-like recording medium (hereinafter referred to as sheet) to an image forming section. 
     2. Description of the Related Art 
     The sheet feeding device for feeding the sheet to an engine section that performs printing in an ink jet recording apparatus, one form of image forming apparatus, may adopt an auto sheet feeder (ASF) method or a paper feeding cassette method. In the ASF method, the sheet directly accommodated in the recording apparatus main body is fed, whereas in the paper feeding cassette method, a cassette is detachably attachable with respect to the recording apparatus main body with the sheets accommodated therein. A sheet feeding device combining the ASF method and the paper feeding cassette method is recently being put to practical use. In cases of large printer or copying machine, in particular, a model in which the sheet feeding devices having the same configuration are arranged in multiple levels to allow the sheets to be selectively fed is put to practical use. 
     With regards to the paper feeding cassette method, it is proposed that a sub-cassette is inserted above the main cassette to allow the sheets of different size to be selectively fed (Japanese Patent Application Laid-Open No. S61-188335). A configuration in which the sub-cassette is arranged overlapping the main cassette and feeding the sheet with separate paper feeding rollers is also proposed (Japanese Patent Application Laid-Open No. H06-40582). When such main cassette and sub-cassette are arranged, the plain papers such as A4 size are set in the main cassette and the thick L-size photo recording papers or post cards are set in the sub-cassette in many cases. 
     There are various types of sheets in recent years, and even printers and the like are able to respond to various printing. In particular, since the ink jet printer is a non-contact printing, the types of sheets are rarely limited, and thus the size and types of sheets are further increased, and the frequency of changing the sheets to be mounted accordingly becomes extremely high. A configuration in which a plurality of sheet feeding devices can be mounted so as to respond to sheets of different sizes even for a relatively low cost type printer is desired. 
     Behaviors exhibited by sheets during transportation also vary due to diversification. For instance, sheets such as ink jet post cards, glossy post cards, cards and business card size having a liquid ink receiving layer show the following behavior. Immediately after applying liquid ink during printing, some sheets greatly warp once and then curl, but such curl decreases and disappears with time and restores to its original shape. Since A4 sheets and the like having a size greater than the post card have a large sheet weight, large curls as seen in the sheet of small size are not produced. When curls are produced, the succeeding sheet may eject the previous first sheet together or the succeeding sheet may rub against the recorded surface of the previous sheet when ejecting the succeeding second sheet. In order to prevent such disadvantages, the step difference from the sheet ejecting port to the mounting surface of the ejected paper tray is sufficiently secured in the prior art even for small printers. However, with the ejected paper tray of a fixed configuration having the position of the sufficient step difference as a fixed position, many disadvantages arise in terms of high stacking performance of adapting to the size and type of the ejected sheet, and allowing as much sheet as possible to be mounted while aligning. 
     An apparatus in which the ejected paper tray is not fixed at the position having a step difference from the sheet ejecting port, and the ejected paper tray is moved in the up an down direction or in the vertical direction with driving means is proposed in order to achieve the ejected paper tray of high stacking performance (Japanese Patent Application Laid-Open No. H05-17064). Further, a configuration in which the plain cut papers are mounted on the main bottom plate of the ejected paper tray, and envelopes and the like are mounted on a sub-bottom plate arranged at one part of the main bottom plate to enhance the stacking performance is proposed (Japanese Patent Application Laid-Open No. 2002-87682). In this case, the main bottom plate is supported by a spring from below, and the main bottom plate elastically compresses the spring and sinks in response to the weight of the sheet. Since the sub-bottom plate is for small envelopes, the spring force of the spring for the sub-bottom plate is large compared to that of the spring for the main bottom plate. Therefore, in the case of envelopes, the spring is compressed by way of the sub-bottom plate after a greater number of papers than the plain cut papers are mounted. Thus, the stacking performance is enhanced even in the case of small envelopes having a sheet thickness of a few times greater than the plain cut paper by mounting a great number of papers. 
     However, the prior arts have the following problems. The sheet feeding device disclosed in Japanese Patent Application Laid-Open No. S61-188335 is troublesome in that the cassette must be changed manually, and the sub-cassette must be taken out and stored each time when using the main cassette. 
     Further, in the case of the sheet feeding device disclosed in Japanese Patent Application Laid-Open No. H06-40582, the occupying space of the sheet feeding device becomes extremely large with respect to the printer main body. 
     Further, with regards to the mounting tray disclosed in Japanese Patent Application Laid-Open No. 2002-87682, if the step difference from the sheet ejecting port to the mounting surface of the ejected paper tray is sufficiently secured so as to correspond to various sheets, the device becomes larger by such amount. In addition, driving means for moving the ejected paper tray up and down is arranged, whereby the device becomes larger and more complicating with increase in the driving motor and the drive transmission means. 
     Moreover, in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. H05-17064, the position in the up and down direction of the main bottom plate and the sub-bottom plate is determined by balancing the spring force of the spring and the sheet mounted weight. Therefore, the sheet mounting amount at the main bottom plate and the sub-bottom plate is not guaranteed if the spring properties of the springs of the main bottom plate and the sub-bottom plate vary. In addition, diversification of the sheet type cannot be responded with a unique spring force. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a sheet feeding device that alleviates the work of the user when changing the cassette, that miniaturizes the device, and that enhances stacking performance of the ejected sheets and the like, and an image forming apparatus. 
     It is an another object of the present invention to provide a sheet feeding device including a cassette type sheet accommodating section that is detachably attachable with respect to the image forming apparatus main body with the sheets accommodated inside, wherein the sheet accommodating section includes a main accommodating part and a sub-accommodating part for simultaneously accommodating sheets of different size, the sub-accommodating part is arranged to be movable in the sheet feeding direction to a cover member for opening and closing the main accommodating part, and the sheet can be fed from the sub-accommodating part while being attached to the image forming apparatus main body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an entire perspective view showing an ink jet printer and a sheet feeding device arranged thereon of an embodiment of an image forming apparatus according to the present invention; 
         FIG. 2  is a perspective view showing a main engine configuration; 
         FIG. 3  is a side cross sectional view showing the engine configuration; 
         FIG. 4  is a perspective view showing a paper feeding cassette as a single body; 
         FIG. 5  is a perspective view showing the paper feeding cassette with a cover in an opened state; 
         FIG. 6  is a plan view showing an internal configuration of the paper feeding cassette; 
         FIG. 7  is a side cross sectional view showing an internal configuration of the paper feeding cassette; 
         FIG. 8  is a perspective view showing a transmission gear train coupled to a printer main body in attaching the paper feeding cassette; 
         FIG. 9  is a cross sectional view showing an engine configuration before attachment of the paper feeding cassette; 
         FIG. 10  is a cross sectional view showing the engine configuration in the paper feeding cassette attached state; 
         FIG. 11  is a cross sectional view showing the engine configuration in paper feeding from a main cassette; 
         FIG. 12  is a cross sectional view showing a state in which the sub-cassette is moved to a paper feeding position; 
         FIG. 13  is a cross sectional view showing the engine configuration during paper feeding from the sub-cassette; 
         FIG. 14  is an exploded perspective view showing a paper feeding cassette according to a second embodiment; 
         FIG. 15  is a perspective view showing a main engine configuration according to a third embodiment; 
         FIG. 16  is a side cross sectional view showing the engine configuration of the third embodiment; 
         FIGS. 17A and 17B  are perspective views showing an ejected paper surface movable plate configuring one part of an ejected paper tray at a fixed position in plain and a position lower than the fixed position, respectively; and 
         FIG. 18  is a cross sectional view in the vicinity of the ejected paper tray with the sub-cassette in the advanced state. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An ink jet printer which is a preferred embodiment of an image forming apparatus according to the present invention and a sheet feeding device arranged in the printer main body will now be described with reference to the drawings. 
     First Embodiment 
     As shown in  FIG. 1 , a paper feeding cassette (sheet accommodating section)  100  configuring the sheet feeding device is detachably removable to a cassette inserting port  5  opened at the front surface of a printer main body  1  while accommodating sheets S. The sheet S in which printing is completed is ejected from a paper ejecting port  26 . 
     In  FIG. 2  showing an internal configuration of the printer main body  1 , a paper feeding unit  2  configuring the sheet feeding device with the paper feeding cassette  100  detachably attachable at below the engine is arranged, and the sheet S from the paper feeding cassette  100  is conveyed to an LF unit  3 . A CR unit  4  includes a carriage  14  mounted with a recording head  23  to implement printing, and is a mechanism for reciprocating the carriage  14  in the sub-scanning direction of the sheet S. Both units of the paper feeding unit  2  and the CR unit  4  each has its own driving motor, and performs printing operation in cooperation. 
       FIG. 3  shows a paper path (sheet conveying path) in printing. A paper feeding roller  12  is a member that picks up and feeds the sheet S from the paper feeding cassette  100  one at a time. The sheet S picked up from the paper feeding cassette  100  is conveyed through the conveying path by conveying rollers  13 ,  15 ,  17 . An LF roller  19 , and pinch rollers  14 ,  16 ,  18 ,  20  are members for sandwiching and forwarding the sheet S between the rollers. The sheet S conveyed to the LF roller  19  is supported by a platen  27 , and conveyed to a position distant by a predetermined distance with respect to the recording head  23 . In synchronization therewith, the carriage reciprocates and an image is formed on the sheet S by the recording head  23  and printing is performed. The paper ejecting roller  21  ejects the printed sheet S, and a spur  22  pushes the sheet S down. The sheet S in which printing is completed is conveyed in the direction of arrow in the figure. An ejected paper tray  25  is extensible according to the size of the ejected sheet S, and mounts and stacks the sheets S. 
       FIG. 4  shows the paper feeding cassette as a single body. The paper feeding cassette  100  includes a main cassette (main accommodating part)  101 , the sheet S 1  of large size such as A4 and the like of plain cut paper being loaded therein, and forwards the sheet S 1  in the paper feeding direction shown with an arrow A. The main cassette  101  is provided with a pushing plate  104  for pushing up the bundle of loaded sheet S from below and pressure contacting the upper most sheet S to the paper feeding roller  12  ( FIG. 3 ). Further, a cover  102  that covers most part of the main cassette  101  is arranged, which the cover  102  can swing in a direction of opening the main cassette  101  by way of left and right supporting shaft pins  102   a  as shown in  FIG. 5 . A sub-cassette (sub-accommodating part)  103  is built in and housed inside the cover  102 . The sub-cassette  103  is loaded with sheets having a size smaller than sheets S 1  loaded in the main cassette  101 , for example, sheets S 2  such as post cards or of L-size. The sheet S 2  is refilled in a state of  FIG. 4 . The sheets S 2  in time of refill are aligned by being positioned with an end guide  107  and a side guide  108 . 
     As shown in  FIG. 5 , the cover  102  is raised substantially vertically with respect to the main cassette  101  with the supporting shaft pin  102   a  as the swing supporting point, and can be removed along with the supporting shaft pin  102   a  from the main cassette  101  in such raised orientation. The sheets S 1  are refilled to the main cassette  101  in the cover removing state. The refilled sheets S 1  have the sheet edges positioned and aligned by contacting the end guide  105  and a side guide  106 . When the cover  102  is in the closed state (see  FIG. 4 ,  FIG. 6 ,  FIG. 7 ), a nail  102   b  (see  FIG. 4 ) arranged at the distal end of the cover engages the main cassette  101  side thereby locking the cover  102 . 
     The sub-cassette  103  incorporated in the cover  102  is guided by fitting a guide pin  113   a  on the sub-cassette  103  side and a guide shaft  109  to two guide grooves  102   c  ( FIG. 7 ) arranged in the cover  102  and can be moved in the sheet feeding direction. A phase gear  110  is arranged to prevent trouble from occurring at the sub-cassette  102  during the movement. In other words, the guide shaft  109  is arranged in a freely rotating manner to the sub-cassette  102  and both ends of the guide shaft  109  are fitted to the guide groove  102   c . Thus, the phase gear  110  that rotates in phase with both ends of the shaft is geared to a gear rack  102   d  arranged at the roof of the cover  102 . 
     A paper feeding guide  113  for positioning the sheet S 2  loaded in the sub-cassette  103  with the side position (edge) as the reference is arranged, which paper feeding guide  113  is fixed to the sub-cassette  103  with a thin member performed with sheet metal processing and the like. The sheet S 2  is moved to one side by the side guide  108  and the end guide  107  with respect to the reference side. The top plate of the paper feeding guide  113  has the left and the right connected so as to cover to the sheet S 2  to prevent warp of the sheet S 2 . The reference side is opened largely to easily load the sheet of smaller size (card size etc.). The distal end has the distal end aligned by a stop lever  112 . The stop lever  112  is movable in the up and down direction and movably floated by a spring so as to move away from the feeding surface of the sheet S 2  when feeding the sheet from the sub-cassette  103 . Further, the sheet S 2  in the sub-cassette  102  is prevented from accidentally jumping out even if the orientation of the cover  102  is changed by a shutter  111  supported in a freely rotating manner at the cover  102  so as to cover the stop lever  112 . 
     As apparent from  FIG. 6  and  FIG. 8 , a gear rack  103   b  is arranged on the side surface of the sub-cassette  103 , which the gear rack  103   b  is geared with a coupling gear (transmission member)  114  on the rotating shaft arranged on the inner side surface of the cover  102 . The coupling gear  114  gears with a transmission gear  121  arranged on the printer main body  1  side and waits when the paper feeding cassette  100  is inserted and attached to the printer main body  1 . The rotational power is transmitted from the main body driving source to the transmission gear  121 , and converts the rotational power to a linear movement in the sheet feeding direction of the sub-cassette  103  by way of the coupling gear  114  and the gear rack  103   b . A stopper (lock member)  115  is engaged with and detached from the coupling gear  114 , wherein the stopper releases engagement with the coupling gear  114  and releases the lock to allow the coupling gear  114  to rotate in attaching the paper feeding cassette, and engages the coupling gear  114 , as shown in  FIG. 6 , to lock the rotation in taking out the paper feeding cassette. Thus, the sub-cassette  103  is prevented from accidentally moving by locking the rotation of the coupling gear  114  or releasing the lock. 
     In  FIG. 6 , a lever  116  for detecting the sub-cassette  103  is arranged, and is attached at a position that can contact the guide shaft  109  of the sub-cassette  103  to detect whether or not the sub-cassette  103  is in a waiting position (home position). When the sub-cassette  103  moves in the sheet feeding direction and detaches from the guide shaft  109 , the sub-cassette detection lever  116  swings and the height of a detecting part  116   a  changes. The presence of the sub-cassette  103  is detected by a home position sensor  130  by way of a detection lever  131  (see  FIG. 9 ) arranged on the printer main body  1  side, and controls the home position of the sub-cassette  103 . 
       FIG. 8  shows the transmission gear train in attaching the paper feeding cassette. A paper feeding motor  122  for rotatably driving the paper feeding roller  12  is used as a driving source for moving the sub-cassette. In other words, the rotational power of the paper feeding motor  122  is transmitted to the transmission gear train, thereby moving of the sub-cassette  103  from the coupling gear  114  via a gear rack  10   b . The paper feeding motor  122  detaches the paper feeding trigger in reverse rotation, and drives the paper feeding roller  12  and the PF roller in forward rotation, and thus moves the sub-cassette  103  by using only the forward rotation. A switching mechanism  125  for changing the rotating direction from the paper feeding motor  122  or blocking the rotation is arranged in the middle of the transmission gear train, so that the rotation from the paper feeding motor  122  is set to one of the states of forward rotation, reverse rotation, or disconnection. A clutch gear  124  sandwiching the friction clutch is inserted to the gear at a position proximate the final stage of the gear train. Since the switching mechanism  125  is in the “disconnected” state when the paper feeding cassette  100  is attached to the printer main body  1 , the paper feeding motor  122  can be operated without limitation. It should be recognized again that the stopper  115  engaging the coupling gear  114  and locking the rotation is detached and separated from the coupling gear  114  in conjunction with the insertion and attachment operation of the paper feeding cassette  100  to the printer main body  1 , so that lock is released to allow free rotation. 
     (Feeding Operation of Sheet S 1  from the Main Cassette  101 ) 
     From the state of  FIG. 9  showing the state before attachment of the paper feeding cassette, when the paper feeding cassette  100  is inserted to the printer main body  1 , a pressing plate lever  128  lowers so that a pressing plate cam  127  stops at the phase in which the spring (not shown) is in the compressed state. The home position sensor  130  of the sub-cassette  103  detects OFF since detected objects are not found at the detection lever  131 . 
     When the paper feeding cassette  100  is inserted into the printer main body  1  along a rail  132 , a contacting part  115   a  of the stopper  115  contacts a convex part  129  of the printer main body  1  and detaches from the coupling gear  114 , whereby the coupling gear  114  is lock released and becomes rotatable, and the sub-cassette  103  becomes movable. When the paper feeding cassette  100  is further inserted, the coupling gear  114  and the transmission gear  121  are connected so as to be drivable with the driving source of the main body (see  FIG. 8 ). The detection lever  131  contacts the contacting surface  116   a  of the sub-cassette detection lever  116 , and detects the position of the sub-cassette  103  and turns ON. The paper feeding cassette  100  is positioned at the same time as when contacting the paper feeding unit  2 , at which position the attachment of the paper feeding cassette  100  to the printer main body  1  is completed. 
       FIG. 10  shows the paper feeding cassette attached state. The pressing plate  104  of the paper feeding cassette  100  is engaged to a groove arranged in the pressing plate lever  128 . The pressing plate lever  128  and the pressing plate  104  are integrally operable in attachment. The paper feeding path is shown with an arrow in  FIG. 11 . When the paper feeding motor  122  rotates with the paper feeding cassette  100  attached and the paper feeding operation starts, the paper feeding roller  12  is rotated and the pressing plate lever  128  is raised according to the pressing plate cam  127 . The pressing plate  104  of the paper feeding cassette  100  engaging the pressing plate lever  128  is then raised, and the paper feeding roller  12  is pressure contacted to the sheet S 1  mounted on the pressing plate  104 . The sheet S 1  is conveyed by the rotation of the paper feeding roller  12  in this state. Here, the sheet is separated by the separating mechanism, and only one sheet is conveyed. Further, the sheet S 1  is forwarded to the conveying roller  13 . The paper feeding roller  12  stops after one round and the separating mechanism moves away, so that sheet conveyance is continued without being a load. Here, the state of the paper feeding cassette  100  returns to the state of  FIG. 10 . Thereafter, the sheet S 1  reaches the LF roller  19 , and conveyed to the front of the recording head  23  and completes the paper feeding operation. Subsequently, printing is performed while synchronizing the recording head  23  and the LF roller  19  according to the printing data. The sheet S 1  is ejected after the printing is completed and a series of operations are completed. 
     (Feeding Operation of Sheet S 2  from Sub-Cassette  103 ) 
     A switching operation is required to feed the sheet S 2  from the sub-cassette  103 . As shown in  FIG. 10 , the sub-cassette  103  is present at a position farthest with respect to the paper feeding direction in the paper feeding cassette  100 , in the attached state of the paper feeding cassette  100 . The home position sensor  130  arranged in the printer main body  1  detects ON at this stage, and detects that the sub-cassette  103  is at the proper position. In this state, the switching mechanism  125  of gear transmission switches to transmit the rotation from the paper feeding motor  122  to forward rotation and rotatably drives the paper feeding motor  122 , whereby each coupling part operates as shown with an arrow A in  FIG. 8 , and the coupling gear  114  rotates in the direction of the arrow A. The sub-cassette  103  is moved in the paper feeding position direction (arrow A) by the gear rack  103   b  geared with the coupling gear  114 . When the sub-cassette  103  starts to move from the state of  FIG. 11 , the sub-cassette detection lever  116  detaches from the guide shaft  109  of the sub-cassette  103  and swings, and the home position sensor  103  turns OFF. With further motor drive, the sub-cassette  103  moves forwards with the guide shaft  109  and a guide pin  103   a  along the guide groove  102   c  of the cover  102 . Since the phase gear  110  arranged in phase at both ends of the guide shaft  109  moves forward while gearing with the gear rack  102   d  arranged on the cover  102 , it moves smoothly without trouble. When further driven, the stopper lever  112  of the distal end of the sub-cassette  103  slightly lowers along a guide surface  101   b  of the main cassette  101  and moves forward and finally enters into a hole  117  of the PF base, and the sub-cassette  103  moves up to the paper feeding position. 
       FIG. 12  shows a state in which the sub-cassette  103  moved up to the paper feeding position. After the distal end of the sub-cassette  103  contacts, the rotation from the paper feeding motor  122  stops without excess load by the clutch gear  124  of the transmission gear train. Thereafter, the switching mechanism  125  returns to a state in which the drive of the paper feeding motor  122  and the transmission gear train are disconnected. In the waiting position, when the sub-cassette  103  held in the cover  102  moves to the paper feeding position, the guide pin  103   a  on the distal end side is released from the guide, and is thereby guided only by the guide shaft  109 . Thus only the distal end side of the sub-cassette  103  is freely swung with the guide shaft  109  as the center. 
     The sheet S 2  is thereby fed from the sub-cassette  103 .  FIG. 13  shows a state of feeding the sheet S 2  from the sub-cassette  103 . When the paper feeding operation of the pressing plate  104  is performed with the sub-cassette  103  moved up to the paper feeding position, the pressing plate  104  of the main cassette  101  moves upward as shown in the figure, the sub-cassette  103  swings with the guide shaft  109  as the center and the distal end side thereof greatly rises, and pushed against the paper feeding roller  12 . Since the stop lever  112  of the sub-cassette  103  is at a position of the original height without being pushed upward since a distal end  112   a  is inserted into the hole  117  of the PF base, the wall of the feeding side of the sheet S 2  is eliminated. Thus, the sheet S 2  loaded in the sub-cassette  103  is fed and printed similar to the sheet S 1  of the main cassette  101 . 
     When printing is completed, an operation for moving the sub-cassette  103  backwards is performed. When the switching mechanism  125  switches the rotation of the paper feeding motor  122  to reverse rotation and rotates the paper feeding motor  122 , each coupling part operates in the direction shown with an arrow B in  FIG. 8 . The coupling gear  114  rotates in the direction of the arrow B, and moves the sub-cassette  103  in the waiting position direction (arrow B). When the sub-cassette  103  moves backwards, the distal end of the sub-cassette detection lever rides on the guide shaft  109  and swings, and the home position sensor  130  turns ON through the detection lever  131  and stops at the waiting position shown in  FIG. 10 . Subsequently, the switching mechanism  125  disconnects the drive transmission from the paper feeding motor  122  to the transmission gear train and returns to the initial state. 
     Therefore, the sub-cassette  103  feeds the sheet S 2  while moving between the waiting position and the paper feeding position. When the paper feeding cassette  100  is removed from the printer main body  1 , the gear train of drive is detached, and at the same time, the coupling gear  114  of the paper feeding cassette  100  is engaged by the stopper  115  and rotation locked, so that the sub-cassette  103  does not accidentally move. In other words, the position of the sub-cassette  103  is not shifted even if the cover  102  is lifted by the user, or the removed paper feeding cassette  100  is left in an arbitrary orientation. Thus, the operation of returning the position of the sub-cassette  103  to the waiting position (home position) every time the paper feeding cassette  100  is attached can be omitted. 
     The movement of the sub-cassette  103  is inhibited by locking the rotation of the coupling gear  114  in the present embodiment, but may be a configuration in which the sub-cassette  103  is directly lock fixed or lock released without the coupling gear  114 . Further, the driving source is not limited to the use of the paper feeding motor  122 , and other motors such as CR, LF and the like may be used. Further, the same effects are obtained when performed by hand. 
     Second Embodiment 
       FIG. 14  shows a second embodiment or an application of the first embodiment. In the first embodiment, a configuration of swinging the cover  102  about the supporting shaft pin  102   a  and removing the cover in a substantially vertically raised orientation with respect to the main cassette  101  is shown. In the second embodiment, on the other hand, a configuration in which the cover  102  is lifted vertically and removed in a state blocking the main cassette  101  is provided. Thus, the main cassette  101  and the sub-cassette  103  are arranged one over the other and the cover  102  is positioned to the main cassette  101  with the positioning pin  11   d , so that the cover itself does not move when moving the sub-cassette  103 . Therefore, in the case of the second embodiment, the cover  102  is easily removed with respect to the main cassette  101  when the paper feeding cassette  100  is removed from the printer main body  1 , thereby enhancing the working convenience when refilling the sheets S 1  to the main cassette  101 . 
     The first and the second embodiments have the advantages described below. 
     (1) The trouble of changing the cassette when feeding the sheet of different size as in the prior art is omitted, and the sheet can be easily and conveniently refilled by simply removing the paper feeding cassette  100  without changing. 
     (2) After the paper feeding cassette  100  is taken out from the printer main body  1 , the sheets can be easily refilled to the main cassette  101  and the sub-cassette  103  since the main cassette  101  can be opened and closed with the cover  102  and can also be detached. 
     (3) Since a power transmission mechanism for receiving power from the driving source of the printer man body  1  and moving the sub-cassette  103  is arranged in the cover  102 , a mechanism for converting the forward/reverse rotational power to a reciprocating movement and moving the sub-cassette  103  forward or backward in the sheet feeding direction is easily configured and power is reliably transmitted. 
     (4) A lock mechanism for preventing the sub-cassette  103  from accidentally moving when taking out the paper feeding cassette  100  is arranged at the cover  102 . Thus, the sub-cassette  103  does not automatically move and the initial position of the sub-cassette  103  is reliably held even if moved in the direction of opening the cover  102  in sheet refilling or changing to the main cassette  101 . 
     (5) When a plurality of paper feeding devices are installed on the printer main body to respond to various types of sheets as in the prior art, the printer main body becomes large, and the manufacturing cost increases. In particular, the image forming apparatus of the present embodiment is suitable for low-cost type for mass consumption, in which case as well, the conventional inconvenience of changing the sheet by hand of the user is improved. 
     Third Embodiment 
       FIGS. 15 to 18  show a third embodiment. The same reference numerals are denoted for the same or common members as those in each of the first and second embodiment, and thus explanation on such redundant portions is not repeated. 
     As shown in  FIG. 15 , an ejected paper tray  200  for stacking the sheets S ejected with printing completed in the printer main body  1  is arranged right above the paper feeding cassette  100 . It includes an ejected paper surface plate  199   a  acting as a partitioning plate to the paper feeding cassette  100  below and configuring the ejected paper tray  200 . The ejected paper surface plate  199   a  is arranged on a frame base  202  of the printer main body  1  through integral molding and the like, and the ejected sheets S are stacked. 
       FIG. 16  shows a paper path (sheet conveying path) in printing. The sheet S is picked up and conveyed from the paper feeding cassette  100  with the paper feeding roller  12 , wherein each member or each device until printed through image forming is as explained in  FIG. 3  in the first embodiment. The sheet S in which printing is completed is ejected in the direction of the arrow in the figure, and mounted and stacked on the ejected paper surface plate  199   a  of the ejected paper tray  200 . 
     A part of the ejected paper surface plate  199   a  is formed as an ejected paper surface movable plate  199   b  corresponding to the stack of the sheet S 2  conveyed from the sub-cassette  103 , printed and then ejected. The ejected paper surface movable plate  199   b  can swing in the up and down direction as shown with an arrow in  FIG. 15  from a swinging hinge part  201  arranged at the boundary to the paper feeding surface plate by its own weight, and a contacting part  203  at the distal end of the moving plate rides on the upper surface of the sub-cassette  103 . 
       FIGS. 17A and 17B  show the fixed position in which the paper feeding surface movable plate  199   b  is substantially in plain with respect to the ejected paper surface plate  199   a , which is integral to the frame base  202 , and the lowered position slightly lowered diagonally from the plain, respectively. That is, in  FIG. 17B , when the sub-cassette  103  moves to the far side of the printer main body, the distal end contacting part  203  of the ejected paper surface movable plate  199   b  that was riding on the sub-cassette  103  until then drops downward by its own weight. Five concave parts  204 , for example, are arranged on the ejected paper surface movable plate  199   b  side, and the dropping movement stops at a position the upper edge of the concave part hooks to an engaging nail  205  arranged at the frame base  202  side. 
     In other words, in the ejected paper tray  200 , the movable plate  199   b  that was at the fixed position in plain with the ejected paper surface plate  199   a  moves downward diagonally (due to movement of the sub-cassette  103  to the far side), and lowers by a few mm in terms of dimension from the plain. Thus, a space depressed into a concave shape in the up and down direction is formed at one part of the ejected paper surface by having one part of the ejected paper tray  200  as the ejected paper surface movable plate  199   b  and lowering the same. Such depressed space is ensured as a sufficient mounting space even if the sheet S 2  (sub-cassette accommodation) that easily curls such as post card is printed and ejected. As a result, the sheet S 2  such as post card that is previously ejected is prevented from being pushed out or being contacted by the succeeding ejected sheet S 2 . 
     (Feeding Operation of Sheet S 1  from Main Cassette  101 ) 
     Similar to the first embodiment, the sub-cassette  103  is at a near side position shown in  FIG. 16  when feeding the sheet S 1  from the main cassette  101 . When the distal end contacting part  203  of the ejected paper surface movable plate  199   b  arranged in the ejected paper tray  200  is on the sub-cassette  103 , the ejected paper surface movable plate  199   b  is at the fixed position at a height substantially in plain with the ejected paper surface plate  199   a . At such in plain height, the ejected paper surface movable plate  199   b  forms an ejected paper surface for stacking the printed sheet S 1  as one part of the ejected paper surface plate  199   a.    
     (Feeding Operation of Sheet S 2  from Sub-Cassette  103 ) 
     Similar to the first embodiment, the sub-cassette  103  advances until contacting the paper feeding position at the far side of the printer main body  1  when feeding the sheet S 2  from the sub-cassette  103 . In a state where the sub-cassette  103  advances, the ejected paper surface movable plate  199   b  on the ejected paper tray  200  side displaces to a position dropped to the lower side as in  FIG. 17B . 
     As shown in  FIG. 18 , the ejected paper surface movable plate  199   b  lowered diagonally is in a positional relationship that partially enters inside the main cassette  101 . Further, the sub-cassette  103  is formed with a cam surface (not shown) on which the distal end contacting part  203  of the ejected paper surface movable plate  199   b  is placed and guided, and the ejected paper surface movable plate  199   b  swings up and down with the movement of the sub-cassette  103 . Therefore, the ejected paper surface movable plate  199   b  is lifted and returns to the upper side position and recovers when the sub-cassette  103  again moves backward. Thus, a series of operations from feeding to ejecting from the sub-cassette  103  are similar to that of the first embodiment with the sub-cassette  103  in the contacting state. 
     As described above, the third embodiment resolves the problems of production of curls that differ depending on whether the sheet S 2  is thick or thin, or on the size and the weight of the sheet; and of rubbing between the previous sheet and the succeeding sheet. In other words, as the ejected paper surface movable plate  199   b  arranged at one part of the ejected paper tray  200  displaces on the lower side and forms a concave depression, a step difference that enlarges the stacking space in the mounting direction is secured. Thus, the rubbing between the first sheet S 2  and the second sheet even for the sheet type that greatly produces curls is avoided. 
     The present invention is not limited to each of the above embodiment, and other embodiments, applications, and variants as well as the combination thereof are also possible within a scope of the principle of the present invention. 
     For instance, in the third embodiment, a configuration in which the ejected paper surface movable plate  199   b  of movable type arranged at one part of the ejected paper surface plate  199   a  configuring the ejected paper tray  200  lowers diagonally by its own weight from the swinging hinge part  201  has been explained. However, it is not limited to the configuration of lowering by its own weight, and a configuration in which the ejected paper surface movable plate  199   b  is biased in the upward direction or the downward direction with a spring member, and moved against the spring member with the movement of the sub-cassette  103  is also possible. Further, a configuration in which the movement in the ejected paper tray  200  becomes unnecessary by directly contacting the sub-cassette  103 , and arranging a cam mechanism and the like for moving the ejected paper tray  200  in the middle of the drive transmission part from the driving source to the sub-cassette  103 , and synchronizing and moving the same may also be adopted. 
     According to the sheet feeding device of the present invention, sheets of different sizes can be simultaneously accommodated in one sheet accommodating section by using a cover member, and the sheet is also fed from the sub-accommodating part in a state attached to the image forming apparatus main body, and thus the trouble of the user changing for every sheet of different size is saved and satisfactory usability is provided. In addition, at least one part of the ejected paper surface of the ejected paper tray for stacking the paper that has been fed from the sub-accommodating part and printed and ejected is lowered in conjunction with the movement of the sub-accommodating part to enlarge the ejected paper space, and the space for stacking is ensured even if curls are produced at the ejected sheet. Thus, enlargement of the entire device is suppressed and the manufacturing cost is reduced by miniaturizing the ejected paper tray. 
     According to the image forming apparatus of the present invention, since sheets of different sizes are accommodated in one removable sheet accommodating section of cassette type and fed through switching, a feeding device for feeding the sheet of different size becomes unnecessary, whereby the entire image forming apparatus is miniaturized by such amount and is particularly suitable for adaptation to low-cost type targeted for the consuming public. 
     This application claims priority from Japanese Patent Application No. 2005-145093 filed May 18, 2005, and Japanese Patent Application No. 2005-261520 filed Sep. 9, 2005 which are hereby incorporated by reference herein.