Patent Publication Number: US-7215921-B2

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus having a buffering device on the upstream side of a sheet processing apparatus and on the downstream side of an image forming portion, and more particularly, to an image forming apparatus whose frame member has a buffering device and a sheet processing apparatus arranged therein. 
   2. Related Background Art 
   Recently, in image forming apparatuses, such as copying machines, printers, facsimile machines, and composite apparatuses composed thereof, there has been an improvement in performance in terms of image quality, number of prints per unit time, etc.; in particular, there has been a marked improvement in printing speed at the time of image formation. In view of this, the interval between the sheets on which image formation is to be performed is set as small as possible. 
   Conventionally, there exists an image forming apparatus, such as a copying machine, a printer, a facsimile machine, or a composite apparatus composed thereof in which a sheet on which an image has been formed on the obverse side (first side) thereof is conveyed again to the image forming portion to form an image thereon. In such an image forming apparatus, there is provided a re-conveying path for conveying a sheet with an image formed on the obverse side (first side) thereof to the image forming portion again to perform image formation on the reverse side (second side) thereof. 
   In such an image forming apparatus, a sheet accommodated in a sheet feeding cassette is fed by a sheet feeding apparatus, and then the sheet is sequentially conveyed to an image forming portion, a fixing portion, and a discharging portion. At that time, if image formation is to be performed on both sides of the sheet or in superimposition on one side thereof, the sheet is conveyed to a re-conveying path to convey it to the image forming portion again. 
   Further, as a conventional image forming system, there is available one having a sheet processing apparatus on the discharge side of the image forming apparatus main body for performing a processing such as binding sheets with images formed thereon; in the case of such an image forming system, in order to improve productivity of the image forming apparatus, there is provided, for example, in a sheet processing path through which sheets are conveyed to the sheet processing portion of the sheet processing apparatus, a buffering device, which is a buffering portion for causing sheets with images formed thereon to stay temporarily while the sheet processing portion is performing sheet processing. 
   By providing such a buffering device in the sheet processing apparatus, while the sheet processing portion is performing the processing operation, a plurality of sheets with images formed thereon are caused to stay temporarily by winding the sheets around a buffer roller provided in the buffering device, thus securing the requisite sheet processing time. In this buffering device, when the processing operation is completed, the plurality of wound sheets are discharged at a time toward the sheet processing portion (see JP 2000-153947 A). 
   Incidentally, in recent image forming apparatuses, the printing speed (the image forming speed) up to the discharge is set high, whereas the discharging speed when discharging and stacking sheets with images formed thereon is set relatively low in order to secure the requisite stacking alignment. For, if the sheets are discharged while maintaining the high printing speed, there is a possibility of the sheets going so far as to interfere with the stacking alignment. Thus, as in the case of securing the sheet processing time, in order to adjust the difference between the printing speed and the discharging speed, it is necessary to cause the sheets with images formed thereon to stay temporarily. 
   Further, in the conventional sheet processing apparatus, as the buffer roller of the buffering device, there is used a large roller having a circumferential length longer than the sheet length so that a plurality of sheets can be properly wound around it. However, when such a large roller is used, the size of the buffering device increases, with the result that the size of the sheet processing apparatus increases. 
   Further, in the sheet processing apparatus, there exist a plurality of sheet conveying paths, such as the sheet processing path, the buffering path provided in the buffering device and formed along the peripheral surface of the buffer roller, the discharging path for conveying sheets with images formed thereon to the discharging portion, and the re-conveying path. When a plurality of sheet conveying path exist in the apparatus main body, not only a rather complicated construction but also an increase in the size of the sheet processing apparatus is involved. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above problems in the conventional art. It is accordingly an object of the present invention to provide an image forming apparatus effective in achieving high productivity. Another object of the present invention is to provide an image forming system which is easily installed in a small space even when a sheet processing apparatus is provided in the image forming apparatus. 
   The present invention provides an image forming apparatus including an image forming portion which forms an image on a sheet, a sheet discharging portion which discharges the sheet with the image formed thereon by the image forming portion, and a buffering device which causes the sheet with the image formed thereon to stay temporarily, wherein the buffering device is provided inside the apparatus main body at a position on the upstream side of the sheet discharging portion with respect to the sheet conveying direction. 
   Thus, in the present invention, a buffering device which causes a sheet with an image formed thereon to stay temporarily is provided inside the frame member of the apparatus main body at a position on the upstream side of the sheet discharging portion with respect to the sheet conveying direction, whereby there is no need to set the image forming speed low so as to adapt it to the sheet discharging speed. Accordingly, it is possible to achieve high productivity. Further, by arranging the buffering device inside the frame member of the apparatus main body, it is possible to achieve miniaturization of the sheet processing apparatus and simplification of the construction thereof, so that, when attaching the sheet processing apparatus to the image forming apparatus, it can be easily attached in a small mounting space, for example, a discharging space provided between the image reading apparatus and the image forming apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram showing the construction of a printer constituting an example of an image forming apparatus according to an embodiment of the present invention; 
       FIG. 2  is a diagram illustrating the construction of a buffering device provided in the printer; 
       FIGS. 3A ,  3 B, and  3 C are first diagrams illustrating the operation of the buffering device; 
       FIGS. 4A ,  4 B, and  4 C are second diagrams illustrating the operation of the buffering device; 
       FIG. 5  is a first diagram showing a construction for jam processing in the buffering device in the above printer; 
       FIG. 6  is a control block diagram of the buffering device; and 
       FIG. 7  is a second diagram showing the construction for jam processing in the buffering device in the above printer. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following, the best mode for carrying out the present invention will be described in detail with reference to the drawings. 
     FIG. 1  is a schematic diagram showing the construction of a printer constituting an example of an image forming apparatus according to an embodiment of the present invention. 
   In  FIG. 1 , a printer  1  constituting the image forming apparatus comprises a printer main body  2 . On top of the printer main body  2 , there is provided an image reader  200  serving as an image reading apparatus, and, inside the printer main body  2 , there is provided an image forming portion  300 . 
   Here, this image reader  200  comprises an original feeding device  100  for feeding originals onto an original plate  102 , and a scanner unit (not shown) for reading the images of the originals fed to the original plate  102 . 
   When reading the original images, the original feeding device  100  feeds one by one the originals (not shown) set face up on an original table  101 , starting with the uppermost original, to the original plate  102 , and, after the images have been read, the originals are discharged onto the a discharge tray  112 . When an original is fed onto the original plate, the scanner unit illuminates the original, and reflection light from the original is guided to an image sensor by way of a mirror and a lens, whereby the image of the original is read. While in this embodiment the image reader  200  is arranged on top of the printer main body  2 , the image reader  200  is not an indispensable component, and the present invention proves effective if applied to an image reading apparatus solely consisting of the printer main body  2 . 
   The image forming portion  300  comprises a photosensitive drum  111 , an exposure control portion  110  which outputs to the photosensitive drum  111  a laser beam corresponding to an image signal that has undergone image processing after the reading by the image sensor to form an electrostatic latent image on the photosensitive drum, a developing device  113  for developing the electrostatic latent image on the photosensitive drum, a transfer portion  116  for transferring to a sheet a toner image developed by the developing device  113 , a fixing portion  117  for performing a toner image fixing processing on the sheet to which the toner image has been transferred, etc. 
   In cassettes  114  and  115  arranged in the lower portion of the printer main body  2 , there are accommodated sheets on which image formation is to be performed. A finisher  400 , which is a sheet processing apparatus for performing a processing on sheets that have undergone image formation, has, in a processing portion for temporarily stacking the sheets that have undergone image formation to perform a processing thereon, a stapler  401 , for instance, which is a processing means for performing a binding processing. 
   In this embodiment, the printer  1  is capable of performing image formation on both sides of a sheet. When performing image formation on both sides of a sheet, the sheet with an image formed on its obverse surface (the first surface) is reversed, and is then passed through a duplex transport path  124  to convey it to the image forming portion  300  again. 
   In the image forming portion  300 , constructed as described above, when, after an original image has been read by the image sensor, an image signal that has undergone image processing is input to the exposure control portion  110 , the exposure control portion  110  applies a laser beam corresponding to the image signal to the photosensitive drum  111 , whereby an electrostatic latent image is formed on the photosensitive drum. 
   Next, the electrostatic latent image on the photosensitive drum is developed by the developing device  113  to form a toner image on the photosensitive drum; thereafter, when a sheet fed from either the cassettes  114  and  115  or the duplex transport path  124  passes a transfer portion  116 , the toner image is transferred to the sheet. Then, in a fixing portion  117 , a toner image fixing processing is performed on the sheet on which the toner image has been thus transferred. 
   When a plurality of sheets are to be output (when there are successive pages), the sheets having passed the fixing portion  117  are guided by a first flapper  121  shown in  FIG. 2  to a first discharging path  122  for conveying sheets to the finisher  400 , and are discharged by discharging rollers  118  to the finisher  400 , with the surfaces with images directed downwards (face down). By thus discharging the sheets face down, the proper page order is maintained when the original feeding apparatus  100  is used or images output from a computer are printed successively starting with the foremost page. When there is no need for a buffering operation described below, for example, when the sheets are to be discharged without undergoing a sheet processing in the finisher  400 , or when no sheets are temporarily stacked in the processing portion of the finisher  400 , the first discharging path  122  is selected by the first flapper  121 . 
   While in this embodiment the finisher  400  is connected and arranged on the downstream side of the discharging roller  118  with respect to the sheet conveying direction, when no finisher  400  is attached, the sheets discharged by the discharging rollers  118  are stacked in a discharging space serving as the mounting space for the finisher  400 . In order that the discharged sheets may not go too far to disturb the stacking alignment, the discharging speed by the discharging rollers  118  is kept lower than the process speed (the printing speed) at which the sheets are conveyed for image formation until they pass the fixing portion  117 . In this embodiment the speed at which the sheets are conveyed inside the finisher  400  when the finisher  400  is mounted is set to be the same as the speed at which the sheets are conveyed by the discharging rollers  118 . However, when the sheet conveying path in the finisher  400  is long, it is possible to increase the sheet conveying speed after the passing of the discharging roller  118  in order to shorten the sheet processing time. 
   In this way, each sheet discharged into the discharging space or sent into the finisher  400  undergoes a temporary reduction in speed at the discharging rollers  118 , so that the interval between this sheet and the subsequent sheet being conveyed at the process speed, which is higher than the discharging speed, is reduced. In order to prevent collision of the preceding sheet and the subsequent sheet, it is necessary to adjust the setting of the difference between the discharging speed and the process speed. When a higher priority is given to stacking alignment, the difference is set smaller, approximating the process speed to the discharging speed. 
   When the number of sheets (pages) to be output is only one (i.e., when there are no successive pages), the sheet is guided to a second discharging path  140  by way of a buffer path  123 , with its surface with a toner image transferred thereto facing upward (i.e., face up), through switching of the flappers  121 ,  130 , and  135 , and is discharged onto a sample tray  131 . That is, in this embodiment, the buffer path  123  constitutes a part of the discharging path for discharging sheets. Further, as described below, this buffer path  123  constitutes a part of a re-conveying path. 
   Incidentally, in this embodiment, there is provided, between the image forming portion  300  and the finisher  400 , a buffering device  600 , which is a buffering portion that causes a plurality of sheets to stay temporarily in order to secure the requisite time for the binding operation so that the conveyance of sheets can be continued even when the finisher  400  is performing the binding operation, and then conveys the sheets toward the finisher  400 . Further, in this embodiment, the buffering device  600  is provided in the frame member of the printer main body  2 . By providing the buffering device  600  inside the frame member of the printer main body  2 , it is also possible to eliminate the problem due to the difference between the discharging speed and the process speed. That is, after causing a plurality of sheets to stay temporarily in the buffering device  600 , the sheets are discharged by the discharging rollers  118 , whereby there is no need to approximate the process speed to the discharging speed to reduce the difference therebetween. 
   Here, this buffering device  600  comprises the buffer path  123  for causing a plurality of sheets to stay temporarily, a buffer roller  601  consisting of a rotary member constituting the guide surface of the buffer path  123  and capable of forward and reverse rotation, the first flapper  121  for guiding a sheet having passed the fixing portion  117  selectively to the buffer path  123  or to the first discharging path  122 , the second and third flappers  130  and  135  which, as described above, guide a sheet having entered the buffer path  123  to the sample tray  131  by way of a second discharging path  140 , fourth through sixth flappers  136 ,  139 , and  137  for causing a sheet having entered the buffer path  123  to enter a third discharging path  142  leading to the finisher  400 , and a seventh flapper  138  for discharging a sheet to the sample tray  131 , with its surface with an image formed thereon facing downwards (i.e., face down). While in this embodiment the buffering device  600  is formed by a rotary member and a buffering path formed on the peripheral surface thereof, it is also possible for the buffering device to be one adapted to retain sheets in a linear fashion. Thus, there are no limitations regarding the configuration of the buffering device as long as it is capable of causing a plurality of sheets to stay temporarily. 
   In this embodiment, as described below, the first through seventh flappers  121 ,  130 ,  135 ,  136 ,  139 ,  137 , and  138 , which are changing means for changing the sheet conveying direction according to the rotating direction of the buffer roller  601 , are provided on the printer main body side. 
   Next, the operation of the buffering device  600 , constructed as described above, will be described. 
   First, a case will be described in which a plurality of sheets are caused to stay and then conveyed to the finisher  400 . 
   In this case, the sheets having passed the fixing portion  117  are guided to the buffer path  123  by the first flapper  121 , which is switched to the position as shown in  FIG. 3A , and are controlled so as to be wound around the buffer roller  601 . In this process, the second through sixth flappers  130 ,  135 ,  136 ,  139 , and  137  are controlled so as to be separated from the buffer roller  601 . At this time, the buffer roller  601  makes reverse rotation, that is, rotates counterclockwise, whereby several sheets are wound around the buffer roller  601 . 
   Next, after several sheets have been wound around the buffer roller  601 , the sixth flapper  137  is controlled so as to abut the buffer roller  601 , whereby the several sheets wound around the buffer roller  601  are guided to the third discharging path  142  to be guided to the finisher  400 . 
   Also when no finisher  400  is mounted, sheets are guided to the discharging space, constituting the mounting space for the finisher  400 , by the same route. 
   Next, a case will be described in which image formation is performed on both side of a sheet. 
   In this case, the sheet first having passed the fixing portion  117  as shown in  FIG. 3B , is guided to the buffer path  123  by the first flapper  121 . At this time, the second and third flappers  130  and  135  are controlled so as to be separated from the buffer roller  601 , and the fourth flapper  136  is controlled so as to abut the buffer roller  601 . When, in this state, the buffer roller  601  rotates counterclockwise, the sheet is guided to a sheet surface reverse path  144  constituting the reversing portion. 
   Thereafter, when the trailing edge of the sheet leaves the second flapper  130 , the second flapper  130  is controlled so as to abut the buffer roller  601  as shown in  FIG. 3C . At the same time, the buffer roller  601  is controlled so as to make forward rotation, that is, to rotate clockwise. As a result, the sheet is guided to the re-conveying paths  143  and  124  by way of the buffer path  123 , and is guided to the transfer portion  116  and the fixing portion  117  for image formation on the other side. 
   Incidentally, by thus rotating the buffer roller  601  to rotate clockwise, it is possible to perform reversal and discharging of a sheet simultaneously. In the following, this will be illustrated. 
   In this case, the sheet having passed the fixing portion  117  first is guided to the buffer path  123  by the first flapper  121 , and the buffer roller  601  is rotated counterclockwise to cause the fourth flapper  136  to abut the buffer roller  601 , controlling the sheet so as to be guided to the reversing path  144 . Next, when the trailing edge of the sheet leaves the second flapper  130 , the second flapper  130  is controlled so as to abut the buffer roller  601  as shown in  FIG. 4A . At the same time, the first flapper  121  is controlled so as to guide the sheet to the first discharging path  122 . At this time, the fifth and sixth flappers  139  and  137  move to the positions as shown in  FIG. 4A . 
   At the same time, the buffer roller  601  rotates clockwise to thereby reverse the sheet existing in the reversing path  144 , guiding it to the re-conveying path  143 . At the same time, the sheet with images formed on both sides thereof is guided to the first discharging path  122 , and is discharged to the finisher  400  side. 
   Next, a case will be described in which a sheet having passed the fixing portion  117  is discharged onto the sample tray  131 . 
   As shown in  FIG. 4B , in this case, the sheet is guided to the buffer path  123  by the first flapper  121 , and the third flapper  135  is controlled so as to abut the buffer roller  601 . By rotating the buffer roller  601  counterclockwise, the sheet is guided to the second discharging path  140 , and is discharged onto the sample tray  131  by the discharging roller  160 . 
   In this case, the sheet is discharged, with its surface to which a toner image has been transferred facing upwards (face up). In the case of a sheet on which image formation has been effected on both sides thereof, it is discharged, with the second surface facing upwards. However, by previously changing the order in which the images are to be written to the sheet by the printer  300 , it is also possible for the sheet to be discharged, with the first surface facing upwards. 
   Further, as shown in  FIG. 4C , when the buffer roller  601  is rotated counterclockwise, guiding the sheet to the buffer path  123  by the first and second flappers  121  and  130 , and guiding the sheet to the reversing path  144  by the third, fourth, and seventh flappers  135 ,  136 , and  138 , and when the trailing edge of the sheet leaves the seventh flapper  138 , the seventh flapper  138  is controlled so as to face upwards. 
   Thereafter, by reversing a conveying roller  161  provided in the reversing path  144 , the sheet is guided to a path  145 , and is discharged onto the sample tray  131  by a discharging roller  160 , with its surface with an image formed thereon facing downwards (face down). 
   Incidentally, in this embodiment, the original feeding apparatus  100  and the image reader  200  are mounted to the printer main body  2  so as to be horizontally slidable. Due to this construction, when jamming occurs in the buffering device, by horizontally sliding the original feeding apparatus  100  and the image reader  200 , it is possible to open a door  101  arranged above the buffering device  600 , making it possible to remove the jammed sheet. 
   Further, in this embodiment, each of the second through sixth flappers  130 ,  135 ,  136 ,  139 , and  137  provided in the printer main body  2  can be selectively moved, by means of a solenoid (not shown) drive-controlled by a control portion  50  serving as a control means as shown in  FIG. 6 , to a first position where it abuts the buffer roller  601  so as to abut the sheet conveyed through the buffer path  123  and to a second position where it is spaced apart from the buffer roller  601  so as not to abut the sheet conveyed through the buffer path  123 . 
   The control portion  50  switches the second through sixth flappers  130 ,  135 ,  136 ,  139 , and  137  to the second positions based on at least one of the following detection signals: a detection signal from a detecting means  51  for detecting sheet jamming in the buffer path, and a detection signal from a door open detecting means  53  for detecting turning off of a power switch  52  for turning the power on and opening of the door  101  to remove the jammed sheet. 
   When thus removing the jammed sheet, by switching the second through sixth flappers  130 ,  135 ,  136 ,  139 , and  137  to the second positions, the jamming can be easily dealt with. 
   Further, in this embodiment, the buffering device  600  is detachably mounted to the printer main body  2 , and, when jamming occurs in the buffering device  600 , a cover  170  on a side surface of the printer main body  2  is caused to slide horizontally as shown in  FIG. 7 , whereby the buffering device  600  can be drawn out integrally with the cover  170 . 
   When thus drawing out the buffering device  600 , the control portion  50  switches at least the second and third flappers  130  and  135 , situated on the downstream side with respect to the drawing-out direction, to the second positions, as shown in  FIG. 7 , based on at least one of the following detection signals: a detection signal from the jamming detecting means  51  and a detection signal from a drawing-out operation detecting means, such as a micro switch (not shown), for detecting turning off of the power switch  52  and drawing-out operation of the buffering device  600 . 
   By thus switching at least the second and third flappers  130  and  135 , situated on the downstream side with respect to the drawing-out direction, to the second positions when drawing out the buffering device  600 , the buffering device  600  can be drawn out easily, and the jammed sheet can be removed easily. 
   Incidentally, by switching the positions of the first through seventh flappers  121 ,  130 ,  135 ,  136 ,  139 ,  137 , and  138 , this control portion  50  switches the sheet conveying direction and controls the forward/reverse rotation of the buffer roller  601 . 
   Through this control of the control portion  50 , the sheet conveying direction is changed as follows: when the buffer roller  601  rotates counterclockwise, it is selectively changed such that the sheet is headed for the reversing path, the sample tray, which is on the downstream side of the second discharging path  140 , or the finisher; and when the buffer roller  601  rotates clockwise, it is selectively changed such that the sheet is headed for the finisher by way of the re-conveying paths  143  and  124 , the finisher, or the image forming portion. 
   Further, by controlling the rotating direction of the buffer roller  601  and the sheet conveying direction changing operation of each flapper, this control portion  50  causes, as stated above, the buffer roller  601  to rotate clockwise, for example, whereby it is possible to simultaneously effect re-conveyance of the sheet to the image forming portion  1  and the conveyance thereof to the finisher  400 . 
   As stated above, the buffer path  123  is formed so as to extend along the peripheral surface of the buffer roller  601 , and, after the clockwise rotation of the buffer roller  601  and image formation, the sheet conveyed to the first discharging path  122  is conveyed to the finisher  400 , and the sheet in the re-conveying path is conveyed in the direction of the image forming portion  1 , whereby, even in a case in which the buffering device  600  and a plurality of sheet conveying paths including the buffer path  123  are provided in the frame member of the printer main body  2 , it is possible to achieve a reduction in the size of the printer  1  and a simplification in the construction thereof. 
   Further, by thus making it possible to simultaneously perform the conveyance and reversal of the sheet, it is possible to improve the printer  1  in terms of productivity. Further, when, as in this embodiment, a plurality of sheet conveying paths are provided, it is possible to freely select the sheet outputting method and the sheet outputting position, whereby a user has a wider choice of options. 
   While in this embodiment the buffering device  600  is arranged inside the printer main body frame, that is, above the image forming portion and in an extension of the longitudinal path passing the transfer portion  116  and the fixing portion  117 , in the present invention this should not be construed restrictively; it may also be arranged in the finisher  400  and on the upstream side of the stapler  401  (see  FIG. 1 ). 
   This application claims priority from Japanese Patent Application No. 2003-415789 filed on Dec. 12, 2003, which is hereby incorporated by reference herein.