Patent Publication Number: US-9890001-B2

Title: Sheet feeding apparatus and printing apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sheet feeding apparatus and a printing apparatus, and more specifically, to a technique for performing sheet feeding by separating stacked sheets from one another using a plurality of separation parts that apply different levels of resistance to fed sheets. 
     Description of the Related Art 
     Sheets used for printing apparatuses such as printers, copy machines, and facsimile machines range from low-rigidity sheets such as plain paper to high-rigidity sheets such as photo paper and postcards. A sheet feeding apparatus has been desired which appropriately feeds such a variety of sheets. Japanese Patent Laid-Open No. 2011-148622 discloses a sheet feeding apparatus that performs sheet feeding by separating sheets from one another using a plurality of separation parts that apply different levels of resistance to fed sheets. More specifically, the sheet feeding apparatus includes the separation parts that are movable with respect to a fixed separation slope and that apply the different levels of resistance based on biasing by springs. When one of the high-rigidity sheets is separated from the other sheets, both the separation part with lower resistance and the separation part with higher resistance are pushed in by the feeding of the sheet and sink into the fixed separation slope, which then allows the sheet to be separated. In this feeding configuration, in particular, when one of the high-rigidity sheets is separated from the other sheets and fed, a load on the sheet is reduced to enable the sheet to be appropriately fed. 
     However, in the sheet feeding apparatus disclosed in Japanese Patent Laid-Open No. 2011-148622, when a bundle of plurality of low-rigidity sheets enters the separation slope, the plurality of separation parts is pushed in against the force of the bias member and sinks into the fixed separation slopes. Thus, even the lower-rigidity sheet is separated by the fixed separation slope, resistance needed for the desired separation fails to be applied to the sheet, resulting in overlap feeding. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a sheet feeding apparatus and a printing apparatus that enable sheets with different levels of rigidity to be individually reliably separated from one another and fed. 
     In a first aspect of the present invention, there is provided a sheet feeding apparatus comprising: a feeding unit configured to feed a sheet by coming into contact with an uppermost sheet of a plurality of stacked sheets; a separation surface being used for separating the sheet fed by the feeding unit; a first separation part that is provide on a part of the separate surface and is configured to switch between a condition in which the first separation part is protruded from the separate surface and the sheet is capable of come into contact with the first separation part and a condition in which the first separation part is retracted from the separate surface and the sheet is not capable of come into contact with the first separation part and to be fixed to each of the two conditions; and a second separation part that is provide on a part of the separate surface and is configured to be movable in a direction from a condition in which the second separation part is protruded from the separate surface and the sheet is capable of come into contact with the second separation part to a condition in which the second separation part is retracted from the separate surface, according to a contact force received from the sheet. 
     In a second aspect of the present invention, there is provided a printing apparatus comprising: a feeding unit configured to feed a sheet by coming into contact with an uppermost sheet of a plurality of stacked sheets; a separation surface being used for separating the sheet fed by the feeding unit; a first separation part that is provide on a part of the separate surface and is configured to switch between a condition in which the first separation part is protruded from the separate surface and the sheet is capable of come into contact with the first separation part and a condition in which the first separation part is retracted from the separate surface and the sheet is not capable of come into contact with the first separation part and to be fixed to each of the two conditions; a second separation part that is provide on a part of the separate surface and is configured to be movable in a direction from a condition in which the second separation part is protruded from the separate surface and the sheet is capable of come into contact with the second separation part to a condition in which the second separation part is retracted from the separate surface, according to a contact force received from the sheet; and a printing unit configured to perform printing to the fed sheet. 
     The above-described configuration enables sheets with different levels of rigidity to be individually reliably separated from one another and fed. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view showing a sheet feeding apparatus according to an embodiment of the present invention, and  FIG. 1B  is a top view showing a sheet feeding section of the sheet feeding apparatus; 
         FIG. 2  is a sectional view of the sheet feeding section shown in  FIG. 1B ; 
         FIG. 3  is a schematic sectional view showing circular-arc-shaped protruding portions formed on upper surfaces of a main separation part and sub separation parts in the sheet feeding apparatus according to the embodiment of the present invention; 
         FIGS. 4A and 4B  are schematic sectional view showing positions selectively taken by the main separation part according to the embodiment of the present invention,  FIG. 4A  showing a position where the main separation part protrudes from a separation slope and  FIG. 4B  showing a position where the main separation part retracts from the separation slope; 
         FIGS. 5A and 5B  are schematic sectional views of positions to which the sub separation parts can be moved by a bias force,  FIG. 5A  showing a position where the sub separation parts protrude from the separation slope and  FIG. 5B  showing a position where the sub separation parts are pushed in by sheets; 
         FIG. 6  is a sectional view showing a general configuration of a printing apparatus with the sheet feeding apparatus according to the embodiment of the present invention mounted therein; 
         FIG. 7  is a block diagram showing a control configuration for the printing apparatus shown in  FIG. 6 ; 
         FIG. 8  is a flowchart illustrating a printing operation including a sheet feeding operation in the printing apparatus according to the embodiment of the present invention; 
         FIG. 9  is a flowchart illustrating details of a position selecting operation illustrated in  FIG. 8 ; 
         FIGS. 10A and 10B  are diagrams illustrating a separating operation for stacked sheets in sheet feeding according to the embodiment of the present invention; 
         FIGS. 11A and 11D  are also diagrams illustrating a separating operation for stacked sheets in sheet feeding according to the embodiment of the present invention; 
         FIGS. 12A and 12B  are also diagrams illustrating the separating operation for the stacked sheets in the sheet feeding according to the embodiment of the present invention; 
         FIGS. 13A to 13C  are also diagrams illustrating the separating operation for the stacked sheets in the sheet feeding according to the embodiment of the present invention; 
         FIGS. 14A and 14B  are also diagrams illustrating the separating operation for the stacked sheets in the sheet feeding according to the embodiment of the present invention; 
         FIGS. 15A and 15B  are also diagrams illustrating the separating operation for the stacked sheets in the sheet feeding according to the embodiment of the present invention; 
         FIGS. 16A and 16B  are also diagrams illustrating the separating operation for the stacked sheets in the sheet feeding according to the embodiment of the present invention; and 
         FIG. 17  is a diagram showing a sheet feeding apparatus according to a modification of the first embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will be described below in detail with reference to the drawings. 
     First Embodiment 
       FIG. 1A  is a perspective view showing a sheet feeding apparatus according to an embodiment of the present invention.  FIG. 1B  is a top view showing a sheet feeding section of the sheet feeding apparatus.  FIG. 2  is a sectional view showing the sheet feeding section. 
     As shown in  FIG. 1A , a sheet feeding apparatus  1  according to the present embodiment includes a cassette  10  in which a plurality of sheets P can be housed so as to be stacked, a pickup roller unit  20  that allows the sheet P to be picked up, and a separation section  30  that allows the uppermost one of the sheets P to be separated from the other sheets and fed. The cassette  10  is provided with a lateral pair of side guides  11  that allows the sheets P to be held so as to align side surfaces of the sheets P with one another. The side guides  11  are configured such that the right and left side guides ( 11   b  and  11   a ) are movable in conjunction with each other. The side guides  11  are also configured so as to fix the center of the sheets P in a width direction (an X direction in  FIG. 1A ). An end guide  12  is also provided to hold the sheets P so as to align trailing ends of the sheets P (an upstream side in a conveying direction). 
     The pickup roller unit  20  is provided above the cassette  10 . The pickup roller unit  20  includes a pickup arm  23  and a drive shaft  22 . The pickup arm  23  is provided so as to be rotatable around the drive shaft  22  and can thus pivot to a position according to the stacking height of the sheets P. A pickup roller  21  is provided at a leading end of the pickup arm  23  to allow the uppermost sheet P to be fed. The pickup roller  21  can be rotated by a driving force transmitted from a driving source not shown in the drawings, via the drive shaft  22  and an idler gear  24 . The pickup arm  23  is provided with a bias member not shown in the drawings, and the bias member allows the pickup roller  21  to be pressed against the sheet P at a predetermined bias force in a standby state. The pickup roller  21  is provided so as to come into abutting contact with the fed sheet at the center thereof in the width direction. 
     The separation section  30  is provided on a downstream side of the cassette  10  in a sheet feeding direction. The separation section  30  is provided with a separation slope (separation surface)  31  and a main separation part  32  that lies opposite to the pickup roller  21  and that corresponds to a central portion of the sheet in the width direction, the main separation part  32  being a part of the separation slope  31 . In the areas of the separation section  30  that are different from the area opposite to the pickup roller  21 , sub separation parts  33  are provided on the right and left of the main separation part  32  at a predetermined distance X 1  from the main separation part  32  such that the sub separation parts  33  are symmetric with respect to the main separation part  32 . The separation slope  31  is disposed at an obtuse angle to a +Y direction in  FIG. 2  to allow a predetermined separating resistance to be applied to the sheet P. The separation slope  31  is set at an angle of 60 to 70 degrees to the +Y direction. 
     Like the separation slope  31 , the main separation part  32  and the sub separation parts  33  are disposed at an obtuse angle to the Y direction in  FIG. 2 . On upper surfaces of the main separation part  32  and the sub separation parts  33 , a plurality of circular-arc-shaped protruding portions  32   a  and  33   a  are formed which are contiguously disposed at a predetermined pitch in a conveying direction on the upper surface as shown in  FIG. 3 . Valley portions  32   b  and  33   b  are each formed between the protruding portions  32   a  and  33   a . The main separation part  32  includes a fixed end  32   c  fixed to a shaft portion  35   a  of a separation slope base  35  so that the fixed end  32   c  can pivot as shown in  FIGS. 4A and 4B . A cam follower  32   d  is provided on a rear surface (opposite to the protruding portions  32   a ) of the main separation part  32 . A cam shaft  34  is rotationally driven to allow the orientation of the main separation part  32  to be changed. That is, the main separation part  32  is configured so as to be able to selectively take a position (position A) where the main separation part  32  protrudes from the separation slope  31  so as to enable the sheet to come into abutting contact with the main separation part  32  as shown in  FIG. 4A  and a position (position B) where the main separation part  32  retracts from the separation slope  31  so as to preclude the sheet from coming into abutting contact with the main separation part  32  as shown in  FIG. 4B . On the other hand, the sub separation parts  33  is configured so as to be movable in the Y direction along a guide portion  35   b  formed in the separation slope base  35  as shown in  FIGS. 5A and 5B . More specifically, a bias force applied, in the Y direction in the figures, by the bias member not shown in the drawings allows the sub separation parts  33  to be biased to a position where the sub separation parts  33  protrude from the separation slope  31  in the standby state. The amount by which the sub separation parts  33  protrude at this time is the same as the amount by which the main separation part  32  protrudes. The bias force applied to the sub separation parts  33  in a −Y direction in the figures is set equal to the separating resistance to be applied to the sheet P being conveyed. That is, when the low-rigidity sheet P is conveyed, the sub separation parts  33  are positioned to protrude from the separation slope  31  as shown in  FIG. 5A . The bias force is also set as follows. In contrast, when a high-rigidity sheet is conveyed, the sub separation parts  33  are pushed in but are positioned to be able to cooperate with the separation slope  31  in applying resistance to the sheet as shown in  FIG. 5B . 
       FIG. 6  is a sectional view showing a general configuration of the printing apparatus with the sheet feeding apparatus  1  according to the present embodiment mounted therein. In  FIG. 6 , a feeding roller  3  feeds the sheet P downstream in the sheet conveying direction, which has been separated from the other sheets and fed by the sheet feeding apparatus  1 . A feeding driven roller  4  applies a bias force toward the feeding roller  3  and sandwiches the sheet P between the feeding driven roller  4  and the feeding roller  3  to generate a feeding force. A sheet detection sensor  2  detects the leading end of the fed sheet P. A conveying roller  5  conveys the sheet P fed by the feeding roller  3  and the feeding driven roller  4  to a position opposite to a print head  7 . A pinch roller  6  applies a bias force toward the conveying roller  5  and sandwiches the sheet P between the pinch roller  6  and the conveying roller  5  to generate a feeding force. 
     The print head  7  ejects ink in yellow, magenta, cyan, and black. A carriage  50  is a carriage on which the print head  7  is mounted and which moves in a direction intersecting the sheet conveying direction. Movement of the carriage  50  allows the print head  7  to scan the sheet P and to eject the ink to the print sheet P conveyed by the conveying roller  5  and a pinch roller  6  for printing. In the printing, a platen  8  supports a back surface of the print sheet P at a position opposite to the print head  7 . 
     A discharge roller  9  discharges the print sheet P printed by the print head  7  to the exterior of the apparatus. At the time of the discharge, spurs  62  and  63  rotate in contact with a print surface of the print sheet printed by the print head  7 . In this case, the spur  63  located downstream of the spur  62  is biased by the discharge roller  9 . On the other hand, the discharge roller  9  is not disposed at a position opposite to the spur  62  located upstream of the spur  63 . The spur  62  prevents the print sheet P from being raised. 
       FIG. 7  is a block diagram showing a general configuration of the printing apparatus of the present embodiment. In  FIG. 7 , an MPU  201  controls operations of the sections and data processing. A ROM  202  stores programs and data executed by the MPU  201 . A RAM  203  temporarily stores processing data executed by the MPU  201  and data received from a host computer  214 . 
     A head driver  207  drives the print head  7  to eject the ink. A carriage motor driver  208  controls driving of a carriage motor  20  serving as a driving source for movement of the carriage  50 . A conveying motor driver  209  controls driving of a conveying motor  205  that is a driving source for the conveying roller  5  and the discharge roller  9 . A feeding motor driver  210  controls driving of a feeding motor  206  that is a driving source for the pickup roller  21  and the feeding roller  3 . 
     When a user orders execution of a printing operation in a host computer  214 , a printer driver  2141  transmits print images and print information such as print image grades to the printing apparatus. The MPU  201  performs the printing operation based on the print information received from the host computer  214  via an I/F section. 
       FIG. 8  is a flowchart illustrating a printing operation including a sheet feeding operation in the printing apparatus of the present embodiment. First, in step S 401 , the position of the main separation part  32  is selected. This position selecting operation is an operation of selectively switching between a state where the main separation part  32  protrudes from the separation slope  31  as shown in  FIG. 4A  (position A) and a state where the separation part  32  retracts from the separation slope  31  as shown in  FIG. 4B  (position B). 
       FIG. 9  is a flowchart illustrating details of the position selecting operation. First, in step S 1 , the process determines whether or not the main separation part  32  is in a position A that is an initial position. When the main separation part  32  is not in the position A, the process proceeds to step S 2  to drive the cam shaft  34  to move the main separation part  32  to the position A. Then, in step S 3 , a sheet feeding mode is checked based on information from the host computer  214 . When the sheet feeding mode is a plain paper mode, the process proceeds to step S 4  to determine again whether or not the main separation part  32  is in the position A. Upon determining, in step S 3 , that the sheet feeding mode is not the plain paper mode, the process proceeds to step S 5  to move the main separation part  32  to a position B. When the process determines, in step S 4 , that the main separation part  32  is not in the position A, then in step S 6 , the main separation part  32  is moved to the position A. As described above, the position of the main separation part  32  is selected. 
     As seen again in  FIG. 8 , in step S 402 , the pickup roller  21  is rotated at a predetermined speed, 7.6 inch/sec in the present embodiment. Thus, the pickup roller  21  rotates to pick up the sheet P, and the feeding roller  3  feeds the sheet P toward the print head  7 . In step S 403 , the sheet detection sensor  2  detects the leading end of the sheet P. Then, in step S 404 , the amount of rotation of the feeding roller  3  is controlled to bring the leading end of the sheet P into abutting contact with a conveying nip portion. Thus, a positional-deviation correcting operation is performed. In step S 405 , a start position setting operation is performed on the sheet P. That is, the amount of rotation of the conveying roller  5  is controlled to convey the sheet P to a print start position with reference to the position of the conveying roller  5  based on the print data. In step S 406 , a printing operation is started in which the print head  7  ejects the ink to the sheet P. Specifically, the sheet P is printed by repeating a conveying operation and an image forming operation (ink ejecting operation); in the conveying operation, the sheet P is intermittently conveyed by the conveying roller  5 , and in the image forming operation, the carriage  50  is moved to allow the print head  7  to scan, while the print head ejects the ink. When the process determines, in step S 407 , that the printing operation on the sheet P is complete, the sheet P is discharged to end the printing operation in step S 408 . 
     The separating operation for the sheet P in the sheet feeding apparatus of the printing apparatus according to the above-described present embodiment will be described with reference to  FIGS. 10A to 16B . 
     When the sheet P is plain paper with a low rigidity, the main separation part  32  is fixed by the cam shaft  34  so as to protrude from the separation slope  31 , that is, in the position A as shown in  FIG. 10A . When the pickup roller  21  is driven and rotated, several of the sheets P stacked in the cassette  10  which include the uppermost sheet are fed toward the separation section  30  as shown in  FIG. 10B . At this time, the number of sheets P fed toward the separation section  30  is determined based on the state of a frictional force exerted between the sheets P at that time; the number may be one or two, or even ten or more. 
     When the leading ends of the sheets P reach the separation section  30 , the sheets P act as shown in  FIGS. 11A , and  11 B. When, for example, the leading ends of two sheets P reach the separation section  30 , and moreover, in this state, the pickup roller  21  rotates to push the leading ends of the two sheets P into the separation section  30 , the leading ends of the sheets P receive resistance from the main separation part  32  and the sub separation parts  33 . At this time, the main separation part  32  is fixed by the cam shaft  34  so as to protrude from the separation slope  31  (a dashed line in  FIG. 11A , represents the surface of the separation slope  31 ). Thus, the leading ends of the two sheets P reliably come into abutting contact with the main separation part  32  as shown in  FIG. 11A . On the other hand, the sub separation parts  33 , which are movable in the Y direction in the figures, are pushed in the Y direction in the figures. However, as shown in  FIG. 11B , the sub separation parts  33  are kept at a distance “h” from the separation slope  31  which prevents the sub separation parts  33  from sinking into the separation slope  31 , due to the balance between the bias force of the bias member biasing the sub separation parts  33  and not shown in the drawings and the push-in force of the two sheets (abutting contact force), and the leading ends of the two sheets P come into abutting contact with the sub separation parts  33  in this state. In other words, both the main separation part  32  and the sub separation parts  33  enable resistance to be applied to the leading ends of the two sheets P, thus exerting a force bending the sheets P on the leading ends of the sheets P. Consequently, the uppermost sheet P is deformed and separated from the other sheets. 
     When the leading ends of more sheets, appropriately 10 sheets P, reach the separation section  30 , the sheets P act as shown in  FIGS. 12A, and 12B . When, for example, the leading ends of 10 sheets P reach the separation section  30 , and moreover the pickup roller  21  rotates to push the leading ends of two sheets P into the separation section  30 , the leading ends of the sheets P receive resistance from the main separation part  32  and the sub separation parts  33 . At this time, the main separation part  32  is fixed by the cam shaft  34  so as to protrude from the separation slope  31  (position A). Thus, the leading ends of the 10 sheets P reliably come into abutting contact with the main separation part  32  as shown in  FIG. 12A . On the other hand, the sub separation parts  33 , which are movable in the Y direction in the figures, are pushed in the Y direction in the figures. However, the fixed main separation part  32  limits movement of the leading ends of the ten sheets P. Thus, as shown in  FIG. 12B , the sub separation parts  33  are kept at a distance “i” (&lt;h) from the separation slope  31  which prevents the sub separation parts  33  from sinking into the separation slope  31 , and the leading ends of the 10 sheets P come into abutting contact with the sub separation parts  33  in this state. In other words, as is the case with the two sheets, both the main separation part  32  and the sub separation parts  33  enable resistance to be applied to the leading ends of the 10 sheets P, thus exerting a force bending the sheets P on the leading ends of the sheets P. Consequently, the uppermost sheet P is deformed and separated from the other sheets. 
     Now, a variation in the behavior of paper when a plurality of sheets P come into abutting contact with the main separation part  32  will be described in conjunction with associated effects of the sub separation parts  33 . A case will be described where the leading ends of 10 sheets P reach the separation section  30 . When the leading ends of 10 sheets P reach the separation section  30 , and moreover the pickup roller  21  rotates to push the leading ends of the 10 sheets P into the separation section  30 , the leading ends of the sheets P receive resistance from the main separation part  32  and the sub separation parts  33 . Since the main separation part  32  is fixed by the cam shaft  34  so as to protrude from the separation slope  31 , in an ideal state, the leading ends of the sheets P are conveyed while sliding on the protruding portions  32   a  of the main separation part  32 . At this time, the leading ends of the sheets P receive the desired resistance from the main separation part  32 , and thus, the uppermost sheet P is deformed and separated from the other sheets. However, since the main separation part  32  is fixed, an instantaneous excessive reaction force (impact force) may be applied to the leading ends of the sheets P. At this time, the sheets P may be deformed before the leading ends of the sheets P slide on the protruding portions  32   a  and the valley portions  32   b  of the main separation part  32  as shown in  FIG. 13B . In this case, the leading ends of the sheets P fail to receive the desired resistance needed for separation, thus from a state shown in  FIG. 13B  to a state shown in  FIG. 13C , the leading ends of the sheets P apparently jump up and down and the plurality of sheets is conveyed without being separated from one another. 
     In contrast, the sub separation parts  33 , which are movable in the Y direction in the figures, are pushed in the Y direction in the figures from a state shown in  FIG. 14A  to a state shown in  FIG. 14B . Thus, the above-described instantaneous excessive reaction force (impact force) acting on the leading ends of the sheets P is relieved by the sub separation parts  33 . As a result, while the leading ends of the sheets P jump up and down on the main separation part  32 , the protruding portions  33   a  and the valley portions  33   b  of the sub separation parts  33  allow the leading ends of the sheets P to be held. The holding of the leading ends of the sheets P by the sub separation parts  33  minimizes the jump of the leading ends of the sheets P. Thus, as shown in  FIG. 15A , the leading ends of the plurality of sheets P come into abutting contact with the main separation part  32  again. That is, the main separation part  32  and the sub separation parts  33  each act to allow resistance to be applied to the leading ends of the sheets P, thus exerting a force bending the sheets P on the leading ends of the sheets P, and the uppermost sheet P is deformed and separated from the other sheets. Furthermore, in the width direction of the sheets P, the pickup roller  21  is provided only on one side of each of the sub separation parts  33  as shown in  FIG. 2 . Consequently, the force by which the sheets push in the sub separation parts  33  can be prevented from being excessively high. Thus, the sub separation parts  33  can be more appropriately restrained from being pushed in by the sheets P, allowing the leading ends of the sheets P to be more reliably held. 
     If the sub separation parts  33  are fixed by the cam shaft  34  similarly to the main separation part  32 , a phenomenon occurs where the leading ends of the sheets P jump up and down, leading to overlap feeding of the sheets P. Even if the fixed sub separation parts  33  enable the leading ends of the sheets P to be held so as to prevent the leading ends from jumping up and down, the pickup roller  21  applies only a weak binding force to the sheets P near the sub separation part  33 , resulting in a significant difference between a time when the uppermost sheet P leaves the sub separation part  33  and a time when the uppermost sheet P leaves the main separation part  32 . As a result, the sheets P are more significantly deformed in the width direction, and the ends of the sheets P are likely to be folded, leading to the high likelihood of a jam. Thus, desirably, the sub separation parts  33  are movable in the Y direction in the figures, and are biased to the position where the sub separation parts  33  protrude from the separation slope  31  in the standby state, by the bias force applied, in the −Y direction in the figures, by the bias member not shown in the drawings. 
     Now, a sheet separating operation performed when the sheets P are photo paper or the like, which has high rigidity, will be described. When the sheets P are photo paper or the like, which has high rigidity, the main separation part  32  is fixed by the cam shaft  34  so as not to protrude from the separation slope  31  but to retract from the separation slope  31  (position B) as shown in  FIG. 16A . Thus, the leading ends of the sheets P come into abutting contact only with the separation slope  31  and the sub separation parts  33 . The separation slope  31  is set to an angle of 60 to 70 degrees so as to apply the desired resistance needed for separation to the leading ends of the sheets P such as photo paper, which has high rigidity. However, the leading ends of the actual sheets P may be curled or have burrs formed during cutting, and thus the simple uniform angle setting may lead to a failure in the separation of the sheets P, resulting in overlap feeding or non-feeding. As shown in  FIG. 16B , the sub separation parts  33  hold the leading ends of the sheets P using the protruding portions  33   a , while applying resistance to the leading ends of the sheets P by the bias force of the bias member not shown in the drawings. Consequently, the leading ends of the sheets P are unsusceptible to the curls or the burrs formed during cutting, and the resistance needed for separation can be stably applied to the leading ends of the sheets P. In other words, the sub separation parts  33  serve to exert a force bending the sheets P on the leading ends of the sheets P, causing the uppermost sheet P to be deformed and separated from the other sheets. 
     In the above-described configuration, the main separation part  32  is provided substantially opposite to the pickup roller  21  so as to correspond substantially to the center of the sheet in the sheet width direction, and the two sub separation parts  33  are provided in the areas of the separation section  30  which are different from the area substantially opposite to the pickup roller  21  in the sheet width direction. However, the present invention is not limited to this configuration, and for example, the embodiment configured as described above may be additionally provided with a further sub separation part  33  at a position away from the center of the sheet in the sheet width direction. In particular, the sub separation part  33  is added so as to deal with a larger sheet width to enable reliable separation to be achieved for the larger sheet size. 
     In the above-described configuration, the plurality of protruding portions  33   a  is contiguously disposed on the surface of the sub separation part  33  in the sheet feeding direction, and the sub separation parts  33  as a whole are movable in the Y direction in the figures with respect to the separation slope base  35 . However, the plurality of protruding portions  33   a  that allow the leading ends of the sheets P to be held may be provided so as to be movable with respect to the fixed separation section (for example, the separation slope  31 ). Furthermore, when a plurality of protruding portions  33   a  is provided so as to be elastically deformable, the protruding portions  33   a  themselves have the function of the sub separation parts  33 , and this form is included in the present invention. 
     As described above, the above-described embodiment allows the resistance needed for separation to be appropriately applied to sheets with different levels of rigidity, thus providing a sheet feeding apparatus that achieves reliable separation. 
     Another Embodiment 
       FIG. 17  is a diagram showing a sheet feeding apparatus according to a modification of the above-described first embodiment. Mainly, to effectively deal with large sheet sizes, the sheet feeding section has two pickup rollers  21  arranged in the sheet width direction. Main separation parts  32  are provided opposite the respective pickup rollers  21 . As indicated in the first embodiment, each of the main separation parts  32  is configured to enable its orientation to be changed and to enable switching between a state where the main separation part  32  protrudes from the separation slope  31  (position A) as shown in  FIG. 4A  and a state where the main separation part  32  retracts from the separation slope  31  (position B) as shown in  FIG. 4B . Sub separation parts  33  are provided in areas of the separation slope  31  that are different from the areas opposite to the pickup rollers  21 . The sub separation parts  33  are provided on the right and left of each of the main separation parts  32  at a predetermined distance X 1  from the main separation part  32 . The sub separation part  33  provided between the two pickup rollers  21  is provided at the distance X 1  from each of the two main separation parts  32 . As shown in  FIGS. 5A and 5B , the sub separation part  33  is movable in the Y direction in the figures along a guide portion  35   b  formed in the separation slope base  35  and is biased to the position where the sub separation part  33  protrudes from the separation slope  31  in the standby state, by the bias force applied, in the −Y direction in the figures, by a bias member not shown in the drawings. The amount by which the sub separation parts  33  protrude at this time is the same as the amount by which the main separation parts  32  protrude. 
     The above-described configuration allows the separation section to be configured to deal with large sheet sizes, providing a sheet feeding apparatus that achieves reliable separation. 
     Yet Another Embodiment 
     The above-described embodiment relates to the form in which the separation section with the separation slope (separation surface), the main separation part, and the sub separation parts is provided in the cassette forming the main body of the sheet feeding apparatus. However, the application of the present invention is not limited to this form. For example, the separation section may be provided in a part of the printing apparatus which is adjacent to the cassette in which sheets are stored. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2014-170342, filed Aug. 25, 2014, which is hereby incorporated by reference wherein in its entirety.