Abstract:
A paper feed unit has a paper feed tray stacking sheets thereon, a primary paper feed roller and a secondary paper feed member, wherein an uppermost sheet among the sheets stacked on the paper feed tray is transferred toward the secondary paper feed member from the primary paper feed roller, a tip end of the sheet then contacts with the secondary paper feed member, and primary paper feed is then completed while the sheet is being bent. A counter rotation stop mechanism, which allows the primary paper feed roller to rotate in a paper feed direction but prevents the primary paper feed roller from rotating in a counter direction to the paper feed direction, and a rotation stop release mechanism, which releases a state in which the primary paper feed roller is prevented from rotating in the counter direction by the counter rotation stop mechanism, are also provided.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a paper feed unit, and more particularly, to a paper feed unit for further feeding a sheet from the position at which the tip end of the sheet contacts with a secondary paper feed member by a primary paper feed roller to complete primary paper feed in a state in which the sheet is being bent. 
     FIG. 7 is schematic structural diagram of a conventional paper feed unit A 1 . 
     In FIG. 7, many print sheets (or sheets)  2  are stacked on the paper feed tray  1  of the paper feed unit A 1 . A scraper roller  3  and a pickup roller  4 , which are primary paper feed rollers, are located above the stacked print sheets  2 . The scraper roller  3  press-contacts with the uppermost print sheet  2  and the pickup roller  4  press-contacts with a stripper tray  5 . 
     The rotary shaft  6  of the pickup roller  4  and the rotary shaft  7  of the scraper roller  3  are coupled to each other by a driving belt V. The pickup roller  4  and the scraper roller  3  are rotated in paper feed rotation direction synchronously with each other by the rotation of the rotary shaft  6  of the pickup roller  4 . 
     A pair of secondary paper feed rollers  8  and  9  are arranged to press-contact with each other on the transfer downstream side of the pickup roller  4 . The paired secondary paper feed rollers  8  and  9  are driven to rotate in opposite rotation directions so as to transfer the print sheet  2  put between the rollers  8  and  9 . 
     Also, a paper feed sensor  10  is provided between the pickup roller  4  and the paired secondary paper feed rollers  8  and  9 . The paper feed sensor  10  detects the tip end of the print sheet  2  transferred from a primary paper feed side. 
     Description will be given to the paper feed operation of the paper feed unit constituted as stated above. 
     When the scraper roller  3  and the pickup roller  4  rotate synchronously with each other, at least the uppermost print sheet  2  press-contacted with the scraper roller  3  is transferred and then the transferred print sheet  2  is transferred to the position between the pickup roller  4  and the stripper tray  5 . 
     Since the print sheet  2  which has been transferred to the position between the pickup roller  4  and the stripper tray  5  is press-contacted with the pickup roller  4 , the sheet  2  is transferred further in response to the rotation of the pickup roller  4 . 
     If it is assumed that a plurality of print sheets  2  are transferred to the position between the pickup roller  4  and the stripper tray  5 , the uppermost print sheet  2  is applied with a transfer force by the rotation of the pickup roller  4  and the lowermost print sheet  2  is applied with a transfer resistance by the stripper tray  5 , whereby only the uppermost print sheet  2  is transferred to the paired secondary paper feed rollers  8  and  9  side. 
     When the paper feed sensor  10  detects the tip end of the print sheet  2  transferred, the rotation of the scraper roller  3  and that of the pickup roller  4  are stopped at the point at which the print sheet  2  has been transferred by a predetermined distance with reference to this detection point. To be specific, the print sheet  2  is contacted with the paired secondary paper feed rollers  8  and  9  while the tip end thereof is put between the paired secondary paper feed rollers  8  and  9 , and transferred further from this contact position. Then, primary paper feed is completed while the print sheet  2  is being bent as shown in FIG.  7 . 
     If the primary paper feed is completed while the print sheet  2  is being bent as stated above and the paired secondary paper feed rollers  8  and  9  are driven to rotate, then the print sheet  2  is put between the paired secondary paper feed rollers  8  and  9  smoothly and surely by the returning force of the bent print sheet  2  for returning to a linear state while eliminating the inclination of the sheet caused by the oblique feed of the sheet during the transfer process. It is, therefore, possible to perform secondary paper feed at accurate, surely timing. 
     SUMMARY OF THE INVENTION 
     However, due to the further studies done by the inventors of the present invention, if the primary paper feed is completed in a state in which the print sheet  2  is being bent as shown in FIG. 7, the pickup roller  4  may be possibly rotated in counter direction by the returning force of the bent paper sheet  2  for returning to a linear state and the rear end of the paper sheet  2  moved in a counter transfer direction may possibly press the paper sheet  2  at the uppermost position of the paper feed tray  1 . If such a phenomenon occurs, the position of the uppermost print sheet  2  on the paper feed tray  1  is disordered by the pressurization and the stability of the next primary paper feed is thereby hampered. If the print sheet  2  is a flexible, hard sheet (e.g., a postcard or a cardboard), in particular, the returning force of the bent print sheet  2  for returning to a linear state is strong and the probability that the position of the uppermost print sheet  2  on the paper feed tray  1  is disordered becomes higher. 
     To cope with the above-stated situation, the inventors of the present invention gave a consideration to a paper feed unit A 2  shown in FIGS. 8 and 9. 
     As shown in FIGS. 8 and 9, the paper feed unit A 2  is constituted such that a one-way clutch  11  is attached to the rotary shaft  6  of a pickup roller  4  compared with the paper feed unit A 1  shown in FIG.  7 . 
     The one-way clutch  11  is supported by a side plate  12  which is provided on a paper feed unit main body side to prevent the rotation of the clutch  11 . The one-way clutch  11  allows the rotation of the rotary shaft  6  of the pickup roller  4  when the rotary shaft  6  rotates in a paper feed rotation direction a. The one-way clutch  11  is locked to the rotary shaft  6  when the rotary shaft  6  thereof rotates in a paper feed counterrotating direction b and applied with a counterrotating force on the side plate  12 , thereby preventing the rotation of the rotary shaft  6 . 
     In FIG. 9, a reference numeral  13  denotes a scraper support member supporting the scraper roller  3 . The scraper support member  13  is rotatably supported by the rotary shaft  6  and constituted so as not to rotate when the rotary shaft  6  rotates. 
     That is to say, in the paper feed unit A 2  stated above, if primary paper feed is completed in a state in which the print sheet  2  is being bent, a pressing force in the counterrotating direction acts on the pickup roller by the returning force of the bent print sheet  2  for returning to a linear state. However, since the counter rotation of this pickup roller  4  is stopped by the one-way clutch  11 , it is possible to suppress the rear end of the primarily fed print sheet  2  from pressing the uppermost print sheet on the paper feed tray  1 . 
     In case of the above-stated paper feed unit A 2 , however, the primarily fed print sheet  2  cannot be transferred in counter direction. Due to this, if the jamming of the primarily fed print sheet  2  occurs, the print sheet  2  which has caused jamming cannot be pulled out from a paper feed tray  1  side. In other words, with the constitution of the paper feed unit A 2 , it is difficult to eliminate the print sheet  2  which has causes jamming. 
     The present invention has been achieved with the above-stated studies. It is, therefore, an object of the present invention to provide a paper feed unit capable of preventing the positions of sheets on a paper feed tray by a primarily fed sheet and also easily removing the sheet which has caused jamming. 
     To obtain the above-stated object, a paper feed unit according to the present invention is provided with: a paper feed tray stacking sheets thereon; a primary paper feed roller; a secondary paper feed member provided downstream to the primary paper feed roller in a transferring direction of the sheets, wherein an uppermost sheet among the sheets stacked on the paper feed tray is transferred toward the secondary paper feed member by rotation of the primary paper feed roller, the sheet is further transferred while a tip end of the sheet contacts with the secondary paper feed member, and primary paper feed is then completed while the sheet is being bent; a counter rotation stop mechanism allowing the primary paper feed roller to rotate in a paper feed direction but preventing the primary paper feed roller from rotating in a counter direction to the paper feed direction; and a rotation stop release mechanism releasing a state in which the primary paper feed roller is prevented from rotating in the counter direction by the counter rotation stop mechanism. 
     Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic structural diagram of a paper feed unit according to an embodiment of the present invention; 
     FIG. 2 is a perspective view of the paper feed unit according to the embodiment, which is seen from a paper feed tray side; 
     FIG. 3 is a perspective view showing members attached to the rotary shaft of the pickup roller of the paper feed unit according to the embodiment; 
     FIG. 4 is a partially cross-sectional front view showing the one-way clutch member, the stopper member and the operation lever for controlling the engagement and disengagement of the one-way clutch member and the stopper member of the paper feed unit according to the embodiment; 
     FIG. 5A is a partially cross-sectional front view showing the one-way clutch member, the stopper member and the operation member in a counter rotation stop state according to the embodiment, and FIG. 5B is a view seen from D 1  of FIG. 5A; 
     FIG. 6A is a partially cross-sectional front view showing the one-way clutch member, the stopper member and the operation lever in a counter rotation stop release state according to the embodiment, and FIG. 6B is a view seen from D 2  of FIG. 6A; 
     FIG. 7 is a schematic structural diagram of a conventional paper feed unit; 
     FIG. 8 is a schematic structural diagram of a paper feed unit according to the studies done by the inventors of the present invention; and 
     FIG. 9 is a plan view of members attached to the rotary shaft of the pickup roller of the paper feed unit shown in FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An preferred embodiment of a paper feed unit according to the present invention will be described hereinafter in detail with reference to FIGS. 1 to  6 B. In this embodiment, description will be given while taking a case of applying a paper feed unit A to the paper feed section SP of a printing machine S as an example. The printing machine S to which the paper feed unit A is applied is suitably exemplified by a stencil printing machine or the like. 
     In FIG. 1, many print sheets (or sheets)  2  are stacked on the per feed tray  1  of the paper feed unit A. A scraper roller  3  and pickup roller  4 , which are primary paper feed rollers, are located above the print sheets  2  thus stacked. The scraper roller press-contacts with the uppermost print sheet  2  and the pickup roller  4  press-contacts with a stripper tray  5 . If necessary and suitable, it is needless to say that a single roller can be used as primary paper feed roller. 
     The rotary shaft  6  of the pickup roller  4  and the rotary shaft  7  of the scraper roller  3  are coupled to each other by a driving belt V. The pickup roller  4  and the scraper roller  3  are rotated in paper feed rotation direction synchronously with each other by the rotation of the rotary shaft  6  of the pickup roller  4 . 
     A pair of secondary paper feed rollers  8  and  9  are arranged to press-contact with each other on the transfer downstream side of the pickup roller  4 . The paired secondary paper feed rollers  8  and  9  are driven to rotate in opposite directions so as to transfer the print sheet  2  put between the rollers  8  and  9 . 
     Also, a paper feed sensor  10  is provided between the pickup roller  4  and the paired secondary paper feed rollers  8  and  9 . The paper feed sensor  10  detects the tip end of the print sheet  2  transferred from a primary paper feed side. 
     Referring further to FIGS. 2 to  6 B, a counter rotation stop mechanism B comprises a stopper member  21  and a one-way clutch member  22  having engagement gear teeth  21   a  and  22   a  on their respective opposite surfaces. 
     Both the stopper member  21  and the one-way clutch member  22  are inserted into the rotary shaft  6 . The stopper member  21  and the one-way clutch member  22  are constituted to be slidable in the axial direction of the rotary shaft  6  while the sliding ranges of the members  21  and  22  are restricted by left and right E rings  23  and  24  and to be movable between an engagement position at which their respective engagement gear teeth  21   a  and  22   a  are engaged with each other and a disengagement position at which the engagement gear teeth  21   a  and  22   a  are away and disengaged from each other. 
     A coiled slide spring  25  which winding shaft is the rotary shaft  6 , is interposed between the E ring  23  and the stopper member  21 . The stopper member  21  is urged against the one-way clutch member  22 , i.e., urged toward the engagement position by the spring force of the slide spring  25 . 
     The stopper member  21  is arranged to allow the rotation of the rotary shaft  6  and engagement protrusions  21   b  on the outer surface of the stopper member  21  are inserted into the engagement hole  26   a  of a side plate  26  on a paper feed unit main body side, whereby the stopper member  21  is unable to rotate toward the side plate  26 . 
     An inclined face  21   c  is provided on the one-way clutch  22 -side circumferential side surface of the stopper member  21 . 
     The one-way clutch member  22  is constituted to allow the rotation of the rotary shaft  6  when the rotary shaft  6  rotates in a paper feed rotation direction a and to be locked to the rotary shaft  6  when the rotary shaft  6  rotates in a paper feed counterrotating direction b. 
     A rotation stop release mechanism C is provided at the rotary shaft  6 . The mechanism C comprises the stopper member  21  and an operation lever  30  interposed between the stopper member  21  and the one-way clutch member  22 . 
     The operation lever  30  is provided rotatably around the rotary shaft  6 , which functions as the rotary shaft of the lever  30 , toward the stopper member  21  and the one-way clutch member  22 . An inclined face  30   a  corresponding to the inclined face  21   c  of the stopper member  21  is provided on the stopper member  21 -side of the operation member  30 . 
     As shown in FIGS.  5 A and SB, at the rotation position of the operation member  30  at which position the inclined face  21   c  of the stopper member  21  and the inclined face  30   a  of the operation member  30  entirely contact with each other, the engagement gear teeth  21   a  and  22   a  of the stopper member  21  and the one-way clutch member  22 , respectively, are press-contacted with each other by the spring force of the slide spring  25 . The stopper member  21  and the one-way clutch member  21  are thereby integrated with each other. 
     Accordingly, the stopper member  21  and the one-way clutch member  22  realize, as a whole, a rotation stop state in which the rotation of the rotary shaft  6  in the paper feed counterrotating direction b is prevented. 
     On the other hand, as shown in FIGS. 6A and 6B, at the rotation position of the operation lever  30  at which position the inclined faces  21   c  and  30   a  are entirely out of contact with each other, the stopper member  21  slides in an arrow E direction against the spring force of the slide spring  25  and the engagement gear teeth  21   a  of the stopper member  21  and the engagement gear teeth and  22   a  of the one-way clutch member  22  are away from each other. 
     Accordingly, with the above-stated constitution, the rotation stop state realized by the stopper member  21  and the one-way clutch member  22  is released. 
     That is to say, the operation lever  30  can be rotated between the rotation position shown in FIGS. 5A and 5B and the rotation position shown in FIGS. 6A and 6B while the inclined face  30   a  of the operation lever  30  and the inclined face  21   c  of the stopper member  21  slide on each other. In a normal state, the operation lever  30  is set at the rotation position shown in FIGS. 5A and 5B. 
     A one-way clutch CC is interposed between the pickup roller  4  and the rotary shaft  6 . The one-way clutch CC is constituted so as to turn the rotary shaft  6  and the pickup roller  4  into a driving state, i.e., the rotary shaft  6  and the pickup roller  4  rotate integrally with each other when the rotary shaft  6  is driven in the paper feed rotation direction a, and, on the contrary, to turn the rotary shaft  6  and the pickup roller  4  into a driving free state, i.e., the rotary shaft  6  and also the pickup roller  4  are free from the driving force when the rotary shaft  6  is to be driven in the paper feed counterrotating direction b. 
     Next, the paper feed operation of the paper feed unit constituted as stated above will be described below. 
     When the scraper roller  3  and the pickup roller  4  rotate synchronously with each other, at least the uppermost print sheet  2  press-contacted with the scraper roller  3  is transferred in X 1  direction and then the transferred print sheet  2  is transferred to the position between the pickup roller  4  and the stripper tray  5 . 
     Since the print sheet  2  which has been transferred to the position between the pickup roller  4  and the stripper tray  5  is press-contacted by the pickup roller  4 , the sheet  2  is transferred further in response to the rotation of the pickup roller  4 . 
     If it is assumed that a plurality of print sheets  2  are transferred to the position between the pickup roller  4  and the stripper tray  5 , the uppermost print sheet  2  is applied with a transfer force by the rotation of the pickup roller  4  and the lowermost print sheet  2  is applied with a transfer resistance by the stripper tray  5 , whereby only the uppermost print sheet  2  is transferred to the paired secondary paper feed rollers  8  and  9  side. 
     Then, when the paper feed sensor  10  detects the tip end of the print sheet  2  transferred, the rotation of the scraper roller  3  and that of the pickup roller  4  are stopped at the point at which the print sheet  2  has been transferred by a predetermined distance with reference to this detection point. To be specific, the print sheet  2  is contacted with the paired secondary paper feed rollers  8  and  9  while the tip end thereof is put between the paired secondary paper feed rollers  8  and  9 , and transferred further from this contact position. Then, primary paper feed is completed while the print sheet  2  is being bent as shown in FIG.  1 . 
     Following the primary paper feed, secondary paper feed is started at predetermined timing and the paired secondary paper feed rollers  8  and  9  are driven to rotate. When the paired secondary paper feed rollers  8  and  9  are thus driven to rotate, the bent print sheet  2  is put between the paired secondary paper feed rollers  8  and  9  smoothly and surely by the returning force of the print sheet  2  for returning to a linear state. The secondary paper feed is, therefore, performed accurately and surely. On the other hand, the rear end of the print sheet  2  which has been fed primarily is press-contacted with the pickup roller  4 . Since the pickup roller  4  can be rotated in the paper feed rotation direction a, smooth secondary paper feed operation is surely allowed. 
     Meanwhile, when the primary paper feed is completed in a state in which the print sheet  2  is being bent in the course of the above-stated paper feed operation, a pressing force in the counterrotating direction acts on the pickup roller  4  by the returning force of the bent print sheet  2  for returning to a linear state as shown in arrow X 2  in FIG.  1 . However, the counter rotation of the pickup roller  4  is prevented by the one-way clutch member  22  and the stopper member  21  of the counter rotation stop mechanism B. Due to this, there is not substantially any probability that the rear end of the print sheet  2  which has been primarily fed presses the uppermost print sheet  2  on the paper feed tray  1 . 
     To be specific, if a rotation force in the paper feed counterrotating direction b acts on the pickup roller  4 , the force then acts on the one-way clutch member  22  through the rotary shaft  6 . Although the one-way clutch member  22  intends to rotate by this force, the rotation of the pickup roller  4  is prevented. This is because the engagement gear teeth  22   a  of the one-way clutch member  22  and the engagement gear teeth  21   a  of the stopper member  21  are engaged with each other at the position, shown in FIGS. 5A and 5B, at which the inclined face  21   c  of the stopper member  21  and the inclined face  30   a  of the operation lever  30  entirely contact with each other. 
     Further, if the jamming of the primarily fed print sheets  2  occurs, the operation lever  30  is rotated from the position shown in FIGS. 5A and 5B to the position shown in FIGS. 6A and 6B. Then, the engagement gear teeth  22   a  of the one-way clutch member  22  and the engagement gear teeth  21   a  of the stopper member  21  are disengaged from each other. As a result, even if a rotation force in the paper feed counterrotating direction b acts on the rotary shaft  6 , the one-way clutch member  22  itself freely rotates together with the rotary shaft  6 . Accordingly, the print sheet  2  is not stopped by the one-way clutch member  22  and the stopper member  21 . 
     Thus, even if sheet jamming occurs, it is possible to ensure pulling out the print sheet  2  which has caused jamming from the paper feed tray  1 . 
     After removing the print sheet  2  which has caused jamming, the force applied to the operation lever  30  is released so that the lever  30  is located at the position shown in FIGS. 6A and 6B. Then, the operation lever  30  automatically returns to the position shown in FIGS. 5A and 5B by the reactive force of the slide spring  25 . 
     In this embodiment, the counter rotation stop mechanism B comprises the one-way clutch member  22  and the stopper member  21 . Needless to say, the mechanism B should not be limited to this constitution. Any mechanisms which allow the rotation of the rotary shaft  6  in the paper feed rotation direction a and stop the rotation thereof in the paper feed counterrotating direction b are available. 
     Furthermore, while the rotation stop release mechanism C comprises the operation lever  30  in this embodiment, the mechanism C should not be limited to this constitution. Any mechanisms which can release the rotation stop operation of the counter rotation stop mechanism B are available. 
     Further, while description has been given to a case where the paper feed unit A is applied to the paper feed section SP of the stencil printing machine S in this embodiment, the present invention should not be limited thereto. Even a printing machine and a copying machine other than the stencil printing machine are available if the machines are each provided with a paper feed section for feeding print sheets  2  stacked on a paper feed tray one by one. 
     As stated above, according to the constitution of this embodiment, if the primary paper feed is completed in a state in which the print sheet is being bent, a pressing force in the counterrotating direction acts on the primary paper feed roller by the returning force of the bent paper sheet for returning to a linear state. If the counter rotation of the primary paper feed roller is stopped by the counter rotation stop mechanism and the rotation stop operation of this counter rotation stop mechanism is released by the rotation stop release mechanism and a tensile force for pulling the primarily fed sheet is applied from the paper feed tray side with a hand or the like, then the primary paper feed roller rotates in the counterrotating direction and the sheet can be pulled out. It is, therefore, possible to effectively prevent the positions of the sheets on the paper feed tray from being disordered by the primarily fed sheet and to easily, surely remove the sheet which has caused jamming during the primary paper feed. 
     Specifically, if the primary paper feed is completed while the sheet is being bent, a pressing force in the counterrotating direction acts on the primary paper feed roller by the returning force of the bent sheet for returning to a linear state. However, the counter rotation of the primary paper feed roller is stopped by the engagement state in which the one-way clutch member and the stopper member are engaged with each other. Besides, if the operation lever turns the on-way clutch member and the stopper member into a disengagement state, the rotation of the one-way clutch member becomes free. As a result, if the primarily fed sheet is pulled out from the paper feed tray side, the primary paper feed roller rotates in the counterrotating direction, thereby making it possible to pull out the sheet. 
     The paper feed unit constituted as stated so far can be appropriately applied to the paper feed section of a printing machine. 
     The entire content of a Patent Application No. TOKUGAN 2000-145582 with a filing date of May 17, 2000 in Japan is hereby incorporated by reference. 
     Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiment described above will occur to those skilled in the art, in light of the teachings. The scope of the invention is defined with reference to the following claims.