Patent Publication Number: US-8979089-B2

Title: Sheet post-processing apparatus, image forming apparatus and sheet post-processing method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the priority benefit of the next U.S. Provisional Applications: U.S. Provisional Application Ser. Nos. 61/178,423, entitled SHEET FINISHER WITH APPARATUS FOR FORMING IMAGE ON LONG SHEET, to MANO, filed on May 14, 2009, and 61/187,199, entitled IMAGE FORMING APPARATUS, to MANO, filed on Jun. 15, 2009, the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     Embodiments described herein relates generally to a sheet post-processing apparatus, an image forming apparatus, and a sheet conveying method, and a method with which, when the image forming apparatus applies printing to a long sheet, the sheet post-processing apparatus outputs the sheet. 
     BACKGROUND 
     A sheet post-processing apparatus configured to apply post-processing to a sheet is connected to an image forming apparatus such as an MFP (Multi-Functional Peripheral), a copying machine, or a printer. The image forming apparatus forms an image on the sheet and discharges the sheet. The sheet post-processing apparatus executes post-processing such as sorting or stapling on the sheet. 
     Sheets supplied to the sheet post-processing apparatus are cut sheets (cut paper). The cut sheets have sheet sizes. The sheet sizes are classified into plural kinds of standard sizes according to sheet widths and sheet lengths. 
     The sheet widths indicate sheet dimensions in a direction orthogonal to a sheet conveying direction in which the sheets are conveyed. The sheet lengths indicate sheet dimensions in the sheet conveying direction. 
     There are various standard sizes such as ISO (International Standard) A3 and A4, LD (ledger), LT (letter), LG (legal), and tabloid. The tray length of a paper discharge tray is adjusted to any one of all the kinds of standard sizes. 
     In some case, a long sheet having sheet length of, for example, 1200 mm is used for hanger displays in vehicles. 
     When the image forming apparatus forms an image on the long sheet, the long sheet is set on a manual feed tray. The sheet post-processing apparatus conveys the long sheet to an upper paper discharge tray through a space on the upper side. 
     The image forming apparatus prints the long sheet (a special sheet) and outputs the long sheet to the sheet post-processing apparatus. In this case, the size of the long sheet is not a size of a sheet stacked on a fixed tray or a movable tray. Therefore, the sheet post-processing apparatus directly drops and outputs the long sheet onto the floor surface. 
     However, when the printed long sheet is dropped and output onto the floor surface from the sheet post-processing apparatus, the printed long sheet or an image printed on the long sheet is soiled or the long sheet is scratched. 
     When a tray having tray length enough for stacking the long sheet is provided in the sheet post-processing apparatus, the size of the sheet post-processing apparatus becomes excessively large. The tray causes a problem in setting the image forming apparatus and the sheet post-processing apparatus. 
     It is difficult to stack the long sheet on the fixed tray and the movable tray without bending the long sheet and without scratching the long sheet. 
     It is necessary to provide a dedicated member for conveying the long sheet in the sheet post-processing apparatus. In other words, it is necessary to separately provide a component in the sheet post-processing apparatus. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an image forming apparatus and a sheet post-processing apparatus according to a first embodiment; 
         FIG. 2  is a diagram of an internal configuration example of the image forming apparatus and the sheet post-processing apparatus according to the first embodiment; 
         FIG. 3  is an enlarged diagram of the sheet post-processing apparatus according to the first embodiment; 
         FIG. 4  is a partial perspective view of a fixed tray sheet sensor viewed from the outside of a machine body; 
         FIG. 5  is a partial perspective view of a finisher panel; 
         FIG. 6A  is a first flowchart for explaining a post-processing method for standard size sheets of the sheet post-processing apparatus; 
         FIG. 6B  is a second flowchart following  FIG. 6A ; 
         FIG. 7  is a flowchart for explaining a sheet post-processing method according to the first embodiment; 
         FIG. 8  is an enlarged diagram of a main part of a sheet post-processing apparatus according to a second embodiment; 
         FIG. 9A  is a first flowchart for explaining a post-processing method for standard size sheets of the sheet post-processing apparatus; 
         FIG. 9B  is a second flowchart following  FIG. 9A ; 
         FIG. 10  is a flowchart for explaining a sheet post-processing method according to the second embodiment; and 
         FIG. 11  is an enlarged diagram of a main part of a sheet post-processing apparatus according to a third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a sheet post-processing apparatus includes a machine body, a first roller pair, a tray, a second roller pair, a driving unit, an inlet sensor, a receiving unit and a control unit. The machine body has a post-processing mechanism configured to apply post-processing to a sheet. The first roller pair is provided in the machine body and configured to receive a sheet on which an image is formed by an image forming apparatus in a print job and nip and convey the sheet. The tray is provided further on a downstream side in a sheet conveying direction than the first roller pair. On the tray the sheet discharged from the first roller pair is stacked. The second roller pair is provided in a conveying path defined between the tray and the first roller pair and configured to nip and convey the sheet. The driving unit is configured to drive the second roller pair and the first roller pair. The inlet sensor is configured to detect presence or absence of the sheet in the first roller pair driven by the driving unit. The receiving unit is configured to receive, from the image forming apparatus, sheet length information in the sheet conveying direction of the sheet as a target to which the print job is applied. And the control unit is configured to control the driving unit to rotate, if the sheet length information indicates special length and the inlet sensor detects a trailing end of the sheet, at least rollers of the second roller pair a predetermined number of times and stop the rollers, the second roller pair nipping the sheet. 
     According to one embodiment, a sheet post-processing apparatus includes a machine body, a fixed tray and a movable tray. The machine body has a structural shape and apparatus size equivalent to a structural shape and apparatus size of an existing sheet post-processing apparatus. The sheet post-processing apparatus outputs a long sheet printed by an image forming apparatus without bending the long sheet, without dropping the long sheet onto the floor surface, and without scratching the long sheet. 
     Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus and methods. 
     A sheet post-processing apparatus, an image forming apparatus, a sheet post-processing method are explained in detail below with reference to the accompanying drawings as examples. In the figures, the same components are denoted by the same reference numerals and signs and redundant explanation of the components is omitted. 
     (First Embodiment) 
     An image forming apparatus according to a first embodiment is an MFP having a color copying function for an original document. A sheet post-processing apparatus according to the first embodiment is a finisher coupled to the MFP. 
     A sheet post-processing method according to the first embodiment is a method with which the finisher conveys a long sheet when the MFP applies printing to the long sheet. 
     The long sheet indicates a cut sheet having a dimension larger than the tray length of a tray for paper discharge. Alternatively, the long sheet indicates a long cut sheet having sheet length larger than the sheet length of a standard size sheet. 
       FIG. 1  is a perspective view of the MFP and the finisher.  FIG. 2  is a diagram of an internal configuration example of the MET and the finisher.  FIG. 3  is an enlarged diagram of the finisher shown in  FIG. 2 . In these figures, the same components are denoted by the same reference numerals and signs. 
     An MFP  1  forms images on the long sheet and the standard size sheet and conveys the sheets to a finisher  2 . 
     The finisher  2  discharges the long sheet and the standard size sheet without subjecting the long sheet and the standard size sheet to post-processing. The finisher  2  subjects the standard size sheet to the post-processing and discharges the standard size sheet. The post-processing for a sheet indicates stacking, sorting, and stapling for plural pages. 
     A discharge roller pair  3  discharges a printed-out sheet from a discharge port  4 . A supply port  5  of the finisher  2  is connected to the discharge port  4 . 
     The finisher  2  includes an inlet roller pair  6  (a first roller pair) provided near the supply port  5 , a directing member  7  configured to lead a sheet output from the inlet roller pair  6  to an upper space or a lower space, and a sheet inlet sensor  8  (an inlet sensor). 
     The inlet roller pair  6  is the first roller pair configured to receive a sheet from the MFP  1  and conveys and outputs the sheet. The inlet roller pair  6  includes an upper roller  6   a , a lower roller  6   b , and a sheet conveying path motor  6   c  (a driving unit). The sheet conveying path motor  6   c  drives the lower roller  6   b . A stepping motor is used as the sheet conveying path motor  6   c.    
     The sheet inlet sensor  8  detects the passage of the leading end and the trailing end in a conveying direction of a sheet through the inlet roller pair  6 . 
     The directing member  7  is operable to swing around an axis parallel to a depth direction of a machine body  2   a . The depth direction indicates a direction from the front side to the rear side of the machine body  2   a.    
     The upper space and the lower space are formed further on a downstream side in the sheet conveying direction than the directing member  7 . A finisher control unit  13  controls a position around an axis of the directing member  7 . 
     The upper space defines a path for discharging the standard size sheet without subjecting the standard size sheet to the post-processing. The finisher  2  discharges the long sheet to the outside of the machine body  2   a  via the upper space. The lower space defines a path for applying the post-processing to the standard size sheet and discharging the standard size sheet. 
     When the finisher  2  executes the post-processing, the directing member  7  closes the upper space and leads the standard size sheet to a paper feeding roller pair  9  via the lower space. The paper feeding roller pair  9  includes an upper roller  9   a  and a lower roller  9   b.    
     When the finisher  2  does not execute the post-processing, the directing member  7  closes the lower conveying path and leads the long sheet or the standard size sheet to a last roller pair  10  (a second roller pair) via the upper conveying path. 
     The last roller pair  10  includes an upper roller  10   a , a lower roller  10   b , and a motor  10   c  (a driving unit). The motor  10   c  is a motor configured to rotate the lower roller  10   b . A stepping motor is used as the motor  10   c . The upper roller  10   a  is a driven roller. 
     The sheet conveying path motor  6   c , the motor  10   c , and a motor driver IC (Integrated Circuit)  61  (a driving unit) cooperate with one another, whereby function of the driving unit is realized. The driving unit drives to rotate each roller of the inlet roller pair  6  and each roller of the last roller pair  10  independently from each other. The driving unit is controlled by the finisher control unit  13 . 
     The last roller pair  10  discharges the long sheet and the standard size sheet to a fixed tray  11  (a tray). The fixed tray  11  is a last tray provided at a terminal end further on the downstream side in the sheet conveying direction than the inlet roller pair  6 . 
     Specifically, the last roller pair  10  is provided in a conveying path defined between the fixed tray  11  and the inlet roller pair  6 . A sheet conveyed from the inlet roller pair  6  is stacked on the fixed tray  11 . The fixed tray  11  has length corresponding to the standard size sheet. 
     When the standard size sheet is caused to travel to the fixed tray  11 , the last roller pair  10  drops the standard size sheet onto a stack surface of the fixed tray  11 . In the case of the standard size sheet, the last roller pair  10  conveys plural sheets to the fixed tray  11  one after another. 
     A fixed tray sheet sensor  12  (a sheet sensor) provided in an upper part of the fixed tray  11  detects that the fixed tray  11  is full. 
     “Full” indicates a situation in which the last roller pair  9  is stopped in a state in which the long sheet is nipped and a situation in which a bundle of the standard size sheets fills the fixed tray  11 . 
       FIG. 4  is a partial perspective view of the fixed tray sheet sensor  12  viewed from the outside of the machine body  2   a . Reference numerals and signs same as those described to above denote the same components. 
     As an example, the fixed tray sheet sensor  12  includes a shaft  12   a , an actuator  12   b  axially supported by the shaft  12   a , a piece member  12   c  connected to the actuator  12   b , and a sensor  12   d  configured to detect presence or absence of the piece member  12   c.    
     The shaft  12   a  has an axis parallel to the depth direction. 
     The lower surface of the actuator  12   b  comes into contact with the upper surface of the long sheet or the standard size sheet. The actuator  12   b  is applied with upward force by the sheet and rotates around the shaft  12   a.    
     The actuator  12   b  is mainly used in order to prevent misdetection due to the presence of a dead zone and stably detect a state in which a sheet is stacked in the fixed tray  11 . 
     The piece member  12   c  is integrated with the actuator  12   b . When the distal end of the actuator  12   b  is lifted upward, the piece member  12   c  is displaced downward. When the distal end is displaced downward, the piece member  12   c  is displaced upward. 
     The sensor  12   d  is, for example, a photointerrupter and has a laser diode and a photodiode. The sensor  12   d  detects blocking of light according to the position of the piece member  12   c . The sensor  12   d  is electrically connected to the finisher control unit  13  (a control unit). 
     The stopping long sheet bends in a curve. The upper surface of the long sheet presses up the lower surface of the actuator  12   b  to turn on an output of the sensor  12   d . The fixed tray sheet sensor  12  continues to output ON after the long sheet is put in the fixed tray  11 . 
     Alternatively, the sensor output changes from OFF to ON when the fixed tray  11  is filled with the standard size sheets. 
     After causing the last roller pair  10  to convey the long sheet by a predetermined distance, the finisher control unit  13  causes the last roller pair  10  to nip the long sheet and stops the last roller pair  10 . 
     The predetermined distance indicates a traveling distance starting in a portion where the leading end of the long sheet comes into contact with the last roller pair  10  and ending in a position where the trailing end of the long sheet comes into contact with the last roller pair  10 . 
     The finisher control unit  13  stores in advance the number of steps of the sheet conveying path motor  6   c  and the motor  10   c  equivalent to the predetermined distance. 
     As an example, when there is only one kind of the sheet length of the long sheet used for printing, a ROM (Read Only Memory) of the finisher control unit  13  stores the number of steps. 
     When plural kinds of sheet lengths are used, the ROM stores data in which the sheet lengths and the number of steps are associated. Alternatively, when the plural kinds of sheet lengths are used, the ROM stores one or more calculation formulas for calculating the number of steps from the sheet lengths. 
     The stack surface of the fixed tray  11  is inclined. The fixed tray  11  has the upper end on the leading end side of a sheet and the lower end on the trailing end side of the sheet. The stack surface is inclined such that the upper end is higher than the lower end. 
     When the last roller pair  10  conveys the long sheet, the leading end of the long sheet hangs downward with the own weight thereof. When the last roller pair  10  sends the long sheet, the sheet leading end comes into contact with the stack surface and the sheet leading end slides upward on the stack surface. 
     The sheet leading end reaches the upper end of the fixed tray  11  according to the advance of the long sheet. When the last roller pair  10  further sends the long sheet, a total distance of the traveling of the long sheet exceeds the tray length of the fixed tray  11 . 
     The sheet leading end extends beyond the upper end of the fixed tray  11 . The sheet leading end begins to fall downward on a side of the finisher  2  while the long sheet bends the middle portion thereof. 
     When the number of motor steps reaches the number of steps stored in the ROM, the finisher control unit  13  stops the rotation of the motor  10   c . The finisher control unit  13  controls the last roller pair  10  to keep the last roller pair  10  nipping the long sheet. 
     The finisher  2  still holds the long sheet. The long sheet is prevented a falling out from the finisher  2 . 
     A post-processing mechanism for the standard size sheet is explained below. 
     The finisher  2  further includes, as shown in FIGS.  2  and  3 , a waiting tray  15 , a processing tray  16 , a stapler  17 , a paper discharge tray  18 , and a finisher panel  19 . 
     The waiting tray  15  has two guide members movable along the depth direction of the machine body  2   a . The guide members have wall sections opposed to each other and supporting sections configured to support the lower surface of a sheet. The waiting tray  15  separates the guide members from each other according to belt driving or the like to thereby cause the sheet to fall with the own weight thereof. 
     The processing tray  16  is arranged below the waiting tray  15 . The sheet fallen from the waiting tray  15  is stacked on the processing tray  16 . 
     Not-shown another roller pair leads the sheet on the processing tray  16  to the stapler  17 . The processing tray  16  aligns edges of plural sheets until the stapler  17  completes stapling. 
     A paddle  20  is provided obliquely below the waiting tray  15 . The paddle  20  is located in a position to which the trailing ends in the conveying direction of the sheets fall. The paddle  20  rotates around an axis parallel to the depth direction to support the alignment of the edges of the sheets. 
     A stopper  21  is provided at the end on the stapler  17  side of the processing tray  16 . The stopper  21  regulates the positions of the trailing ends of the sheets. 
     A conveyor belt  22  and a discharge roller  23  are provided below the processing tray  16 . The conveyor belt  22  is driven to travel by two pulleys. The conveyor belt  22  conveys sorted or stapled sheets to the paper discharge tray  18 . The conveyor belt  22  discharges the sheets to the paper discharge tray  18  from a discharge port  24 . 
     The sheet on the waiting tray  15  may be discharged to the paper discharge tray  18  from the discharge port  24  by another roller pair  25  without being stapled. 
     The finisher control unit  13  controls the driving of the sheet conveying path motor  6   c  and the motor  10   c . The finisher control unit  13  also controls a transmission mechanism for driving force generated by the sheet conveying path motor  6   c  and the motor  10   c.    
     As an example, the finisher control unit  13  synchronizes the rotation of the sheet conveying path motor  6   c  and the rotation of the motor  10   c.    
     Alternatively, a clutch is provided between the motor  10   c  and the lower roller  10   b  in advance. When the finisher control unit  13  rotates the sheet conveying path moor  6   c , the finisher control unit  13  disengages the motor  10   c  and the lower roller  10   b  with the clutch. 
     The finisher control unit  13  includes a CPU (Central Processing Unit), a ROM, and a RAM (Random Access Memory). The finisher control unit  13  controls the operation of the finisher panel  19 . 
     The finisher panel  19  receives an instruction by user operation and displays information. The finisher panel  19  is provided in an upper part of the finisher  2 . 
       FIG. 5  is a partial perspective view of the finisher panel  19 . 
     The finisher panel  19  includes a position selection button  26 , a start button  27 , an LED (Light Emitting Diode)  28 , a confirmation button  29 , and plural other LEDs  30 . The finisher panel  19  also includes circuits for power supply and for driving. 
     The position selection button  26  is a direction key for selecting a position of stapling for sheets. The start button  27  is a key for starting the stapling. 
     The LED  28  configures a first display unit configured to display FULL. The LED  28  displays display data received from the finisher control unit  13 . 
     As an example, the LED  28  is covered with a film member of synthetic resin on the like. A character string is silk-printed on the rear surface of the film member. The character string is “fixed tray sheet stack FULL” or the like. An area of plural character sections transmits a beam of light. An area different from the characters does not transmit a beam of light. 
     Alternatively, the finisher panel  19  may include a display device having a display function. 
     When notified that sheet length is large from the finisher control unit  13 , the LED  28  is turned on and indicates that the last roller pair  10  nips the long sheet. The LED  28  informs a user that the long sheet should be removed from the finisher  2 . 
     The confirmation button  29  is a key for the user to input confirmation concerning display by the LED  28 . The other LEDs  30  are turned on or turned on and off according to content of operation of the buttons or a state of the finisher  2 . 
     While the last roller pair  10  nips the long sheet, the finisher control unit  13  turns on or turns on and off the LED  28  for notification. 
     When the finisher control unit  13  detects depression operation of the confirmation button  29 , the finisher control unit  13  drives the motor  10   c  for the last roller pair  10 . The long sheet is discharged. The user grasps the long sheet. 
     The finisher  2  is mainly explained above. The MFP  1  is mainly explained below. 
     As shown in  FIGS. 1 and 2 , the MFP  1  includes a main body  1   a , a scanner unit  31 , an image processing unit  32 , a printer unit  33 , a paper feeding unit  34 , an MFP control unit  35  (a control unit), and a control panel  36 . 
     The machine body  1   a  is connected to the finisher  2 . A manual feed tray  37  is provided on one side of the machine body  1   a . A signal line  14  is wired between the MFP  1  and the finisher  2 . The signal line  14  is a serial communication cable. 
     When an original document is inserted, the scanner unit  31  conveys the original document to a glass table. The scanner unit  31  includes an automatic document feeder, the glass table, a light source, plural carriages respectively having mirrors, a lens, and a photodiode. 
     The light source irradiates the lower surface of the glass table with a laser beam, the carriages move, and the scanner unit  31  scans a document surface. The lens causes a reflected beam from the mirror to converge. The photodiode photoelectrically converts the beam from the lens. The scanner unit  31  converts read image information into an analog signal. 
     The image processing unit  32  is an LSI (Large Scale Integration) configured to convert image data of three colors from the scanner unit  31  into four print colors. 
     The printer unit  33  forms an image on the long sheet or the standard size sheet and outputs the sheet. 
     The paper feeding unit  34  feeds a sheet to the printer unit  33 . The paper feeding unit  34  includes plural stages of trays  34   a  in which sheets of standard sizes such as A3 and A4 are set and pickup rollers  34   b.    
     The MFP control unit  35  is a main control unit configured to control the operation of the entire MFP  1 . The MFP control unit  35  generates a print job. The printer unit  33  forms an image on a sheet according to the print job. 
     The MFP control unit  35  causes the finisher control unit  13  to execute post-processing designated by the print job. The MFP control unit  35  includes a CPU, a ROM, and a RAM. 
     The control panel  36  instructs the printer unit  33  to start image formation and instructs the scanner unit  31  to start document reading. The control panel  36  outputs a signal including various operation inputs, settings, and selection items to the MFP control unit  35 . 
     The control panel  36  includes a display panel  38  (a second display unit). The display panel  38  displays various kinds of information received from the MFP control unit  35 . The display panel  38  displays a dialog screen for urging the user to input the sheet length of the long sheet. The display panel  38  may display a dialog screen for causing the user to select any one of plural kinds of size information of long sheets stored in advance. 
     The manual feed tray  37  opens and closes around a shaft  37   a  horizontally provided on a side of the machine body  1   a . The manual feed tray  37  includes a sensor  37   b  configured to detect which of a closed position and an open position the position of the manual feed tray  37  is. The sensor  37   b  is a micro switch. 
     When the manual feed tray  37  is expanded, the MFP control unit  35  detects a sensor output. When sheet length of the long sheet is input or selected through the control panel  36 , the MFP control unit  35  transmits sheet length information to the finisher control unit  13  of the finisher  2  through the signal line  14 . 
     UARTs (Universal Asynchronous Receiver/Transmitters)  39   a  and  39   b  are respectively provided in a terminal on the MFP  1  side and a terminal on the finisher  2  side of the signal line  14 . The UART  39   a  (a transmitting unit) on the MFP  1  side and the UART  39   b  (a receiving unit) on the finisher  2  side are serial communication controllers. 
     The MFP control unit  35  and the finisher control unit  13  are enabled to transmit and receive information by the UART  39   a , the signal line  14 , and the UART  39   b.    
     One of the UARTs  39   a  and  39   b  requests the other to perform communication and the other responds to the request, whereby a data link of asynchronous serial communication is established between the MFP control unit  35  and the finisher control unit  13 . 
     The UART  39   a  as the transmitting unit transmits sheet length information of a sheet as a target of application of a print job to the finisher  2 . The MFP control unit  35  as a control unit causes the UART  39   a  to transmit information (sheet length information) indicating that a sheet to be printed is the long sheet. 
     When the long sheet is inserted into the manual feed tray  37  or when an instruction is given to the control panel  36  by user operation, the MFP control unit  35  transmits information indicating the long sheet to the finisher control unit  13 . 
     The UART  39   b  as the receiving unit receives the size information of the sheet and timing for starting driving of the inlet roller pair  6  from the MFP  1 . The UART  39   b  as the transmitting unit transmits a control signal to the MFP  1 . 
     When the size information received from the UART  39   b  indicates large length (special length) and the inlet sensor  8  detects the long sheet, the finisher control unit  13  rotates the inlet roller pair  6  and the last roller pair  10  by the number of pulses determined in advance. 
     Thereafter, the finisher control unit  13  controls the motor driver IC  61  to stop the inlet roller pair  6  and the last roller pair  10  in a state in which the last roller pair  10  nips the long sheet. 
     The control on the motor driver IC  61  by the finisher control unit  13  stops the inlet roller pair  6  and the last roller pair  10  at timing when the inlet roller pair  6  nips the trailing end of the long sheet. 
     The printer unit  33  is further explained below. 
     The printer unit  33  includes image forming units  41 Y,  41 M,  41 C, and  41 K for yellow (Y), magenta (M), cyan (C), and black (K), which are provided in parallel along an intermediate transfer belt  40 , and a laser exposure device  42 . 
     The image forming unit  41 K includes a photoconductive drum  43 , a charger  44 , a developing device  45 , and a transfer device  46 . The photoconductive drum  43  holds a latent image. The charger  44  uniformly charges a photoconductor of the photoconductive drum  43 . The laser exposure device  42  forms a latent image on the photoconductive drum  43 . The developing device  45  develops the latent image on the photoconductive drum  43 . The transfer device  46  transfers a developer image on the photoconductive drum  43  onto the intermediate transfer belt  40 . 
     The configurations of the image forming units  41 Y,  41 M, and  41 C are substantially the same as the configuration of the image forming unit  41 K. 
     The MFP  1  includes a guide member and plural roller pairs for drawing up the standard size sheet from the paper feeding unit  34 . The guide member and gaps of the plural roller pairs, each having one pair of rollers, define a conveying path for the sheet. 
     The plural roller pairs, a motor for conveyance, and gears configure a conveying mechanism configured to convey the sheet to the conveying path. 
     A roller pair  47  is provided in the manual feed tray  37 . The manual feed tray  37  leads, to the conveying path, the long sheet or the standard size sheet supplied from the outside of the main body  1   a.    
     The MFP  1  includes a secondary transfer roller pair  48  and a fixing device  49 . The secondary transfer roller pair  48  transfers the developer image on the intermediate transfer belt  40  onto the long sheet or the standard size sheet. 
     The fixing device  49  fixes the developer image on the long sheet or the standard size sheet. The fixing device  49  includes a heat roller  49   a  and a press roller  49   b . A driving motor drives the heat roller  49   a . The press roller  49   b  is a driven roller. 
     The fixing device  49  conveys and outputs the sheet at speed instructed by the MFP control unit  35 . Plural roller pairs  50  are provided further on the downstream side in the sheet conveying direction than the fixing device  49 . The fixing device  49  and the roller pairs  50  define another conveying path continuous to the conveying path defined on the paper feeding unit  34  side. 
     The latter conveying path includes a first discharge port  51  and a second discharge port  4 . The first discharge port  51  is opened above the machine body  1   a . The finisher is connected to the second discharge port  4 . The discharge port  4  and the finisher  2  define a conveying path for a sheet. 
     The operation of the MFP  1  and the finisher  2  having the configurations explained above is explained below. A control method for the finisher  2  in discharging a sheet other than the long sheet from the MFP  1  to the fixed tray  11  is explained with reference to  FIGS. 6A and 6B . In the figures, the image forming apparatus indicates the MFP  1  and the post-processing apparatus indicates the finisher  2 . 
       FIG. 6A  is a first flowchart for explaining a post-processing method for the standard size sheet of the finisher  2 .  FIG. 6B  is a second flowchart following  FIG. 6A . 
     Prior to insertion of an original document, in Act A 1 , sheets are set in the manual feed tray  37  of the MFP  1 . Alternatively, sheets are set in any one of the trays of the paper feeding unit  34 . 
     In Act A 2 , the MFP  1  selectively displays a type of a sheet different from the long sheet using the display panel  38 . The display panel  38  urges the user to start printing. 
     In Act A 3 , the MFP  1  starts execution of a print job. When an original document is inserted into the scanner unit  31 , the MFP  1  picks up a sheet from the paper feeding unit  34  and executes an image forming process. 
     In Act A 4 , the MFP  1  notifies the finisher  2  of a processing request for the sheet through the signal line  14 . The processing request includes information for identifying a sheet size, necessity of post-processing, a type of the post-processing, and a tray to which the sheet should be discharged. 
     In Act A 5 , the MFP  1  discharges the sheet. 
     When the processing request includes a standard size, unnecessity of the post-processing, and the fixed tray  11 , the finisher control unit  13  causes the sheet conveying path motor  6   c  of the inlet roller pair  6  to start driving before a predetermined time elapses. 
     The finisher control unit  13  causes the directing member  7  to close the lower conveying path. The finisher control unit  13  causes the motor  10   c  of the last roller pair  10  to start driving. 
     The sheet inlet sensor  8  detects the leading end of the sheet. The finisher control unit  13  receives the input of ON from the sheet inlet sensor  8 . Thereafter, the fixed tray sheet sensor  12  starts to detect the leading end of the sheet. The finisher control unit  13  receives the input of ON from the fixed tray sheet sensor  12 . 
     In Act A 6 , the finisher control unit  13  detects that the sheet conveying path motor  6   c  is operating and that both the sheet inlet sensor  8  and the fixed tray sheet sensor  12  are on. 
     In Act A 7 , the finisher control unit  13  determines whether the sensor output of the sheet inlet sensor  8  changes from ON to OFF. While the sensor output does not change, through the NO route, the finisher control unit  13  repeats the processing in Act A 6 . 
     If the sensor output changes from ON to OFF, through the YES route (see a section marked A in the figure), the finisher control unit  13  drives the sheet conveying path motor  6   c  in Act A 8  in  FIG. 6B . The finisher  2  continues the discharge of the sheet to the fixed tray  11 . The finisher control unit  13  continues feeding of the sheet by continuing to drive the motor  10   c.    
     In Act A 9 , the finisher control unit  13  monitors whether the sensor output of the fixed tray sheet sensor  12  changes from ON to OFF. 
     The leading end of a cut sheet pushes up the leading end of the actuator  12   b  of the fixed tray sheet sensor  12 . Thereafter, when the cut sheet drops to the stack surface of the fixed tray  11 , the long sheet leading end falls. 
     Since cut sheets are conveyed one after another, the distal end of the fixed tray sheet sensor  12  repeats the rise and the fall. While the change is repeated, the finisher  2  continues to discharge the sheet (the YES route in Act A 9 ). 
     In a state in which the distal end of the actuator  12   b  rises, the fixed tray sheet sensor  12  continues to output the same sensor value. 
     When the change does not occur and time in which the sensor output of the fixed tray sheet sensor  12  indicates ON continues exceeding a time threshold stored in advance, through the NO route in Act A 9 , the finisher control unit  13  turns on or turns on and off the LED  28  of the finisher panel  19  in Act  10 . The finisher panel  19  displays “fixed tray sheet stack FULL”. 
     In Act A 11 , the finisher  2  notifies the MFP  1  that “full” is detected. The finisher control unit  13  stops the job of the finisher  2 . The MFP  1  stops the execution of the print job. 
     The user removes a bundle of sheets from the fixed tray  11 . The distal end position of the actuator  12   b  changes from the upper position to the lower position with the own weight of the actuator  12   b . The piece member  12   c  in the fallen state moves upward. 
     In Act A 12 , the finisher control unit  13  detects, on the basis of the output of the fixed tray sheet sensor  12 , that the bundle of sheets is removed. The finisher control unit  13  stops the display of the finisher panel  19 . 
     In Act A 13 , the finisher control unit  13  determines whether the sensor output of the fixed tray sheet sensor  12  changes from ON to OFF. 
     If the sensor output changes to OFF, through the YES route in Act A 13  (see a section marked I), the finisher  2  transmits a message of restoration to the MFP  1  in Act A 3  in  FIG. 6A . The MFP  1  executes the print job. 
     If the finisher control unit  13  determines in Act A 13  in  FIG. 6B  that the fixed tray sheet sensor  12  is not operating, through the NO route, the finisher control unit  13  ends the processing. 
     In  FIGS. 6A and 6B , when the processing request includes an instruction for stapling, the finisher  2  processes sheets in the same manner as the example in which the post-processing is not performed. 
     The finisher control unit  13  causes the paper feeding roller pair  9 , the roller pair on the processing tray  16 , the paddle  20 , the conveyor belt  22 , and the like to operate. The finisher control unit  13  staples pages of sheets conveyed from the MFP  1  one after another and outputs a bundle of the sheets stapled in this way to the paper discharge tray  18 . 
     A post-processing method for the finisher  2  in discharging the long sheet from the MFP  1  to the fixed tray  11  is explained with reference to  FIG. 7 . 
       FIG. 7  is a flowchart for explaining the post-processing method for the long sheet of the finisher  2 . 
     Prior to insertion of an original document, in Act B 1 , long sheets are set in the manual feed tray  37  of the MFP  1 . 
     In Act B 2 , the MFP  1  selectively displays the long sheet using the control panel  36 . The control panel  36  urges the user to start printing. 
     In Act B 3 , the MFP  1  starts execution of a print job. The MFP  1  executes an image forming process on the long sheet. 
     Alternatively, the MFP control unit  35  captures image data from a LAN (Local Area Network), a telephone line, or an externally-attached memory device, whereby the MFP  1  may form an image on the long sheet. 
     In Act B 4 , the MFP  1  notifies the finisher  2  of a processing request for designating the output of the long sheet and the fixed tray  11 . The processing request may include the size of the long sheet. 
     In Act B 5 , the MFP  1  discharges the long sheet. 
     The finisher control unit  13  causes the sheet conveying path motor  6   c  to start driving before a predetermined time elapses. The finisher control unit  13  causes the directing member  7  to close the lower conveying path. The finisher control unit  13  causes the motor  10   c  to start driving. 
     The finisher control unit  13  receives the input of ON from the sheet inlet sensor  8 . Thereafter, the finisher control unit  13  receives the input of ON from the fixed tray sheet sensor  12 . 
     In Act B 6 , the finisher control unit  13  detects that the sheet conveying path motor  6   c  is operating and both the sheet inlet sensor  8  and the fixed tray sheet sensor  12  are on. 
     In Act B 7 , the finisher control unit  13  determines whether the sensor output of the sheet inlet sensor  8  changes from ON to OFF. While the sensor output does not change, through the NO route, the finisher control unit  13  continues to detect the long sheet. 
     If the sensor output changes from ON to OFF in Act B 7 , through the YES route, in Act B 8 , the finisher control unit  13  causes the sheet conveying path motor  6   c  to operate by a specified number of pulses and stops the motor driving. The finisher control unit  13  causes the last roller pair  10  to nip the trailing end of the long sheet. 
     The specified number of pulses is the number of steps of a stepping motor equivalent to a predetermined traveling distance of the long sheet. The predetermined traveling distance indicates a distance short enough for not bringing the leading end of the long sheet into contact with the floor surface. 
     The specified number of pulses mainly depends on the sheet length of the long sheet, the height and the full width in the front of the machine body  2   a , the circumferential length of the inlet roller pair  6 , the circumferential length of the last roller pair  10 , and the like. 
     The finisher control unit  13  causes the motor  10   c  to operate by the specified number of pulses in synchronization with the rotation of the sheet conveying path motor  6   c . Alternatively, the finisher control unit  13  stops only the rotation of the motor  10   c . Alternatively, the finisher control unit  13  interrupts, with clutch control, conveyance force applied to the sheet by the motor  10   c.    
     As shown in  FIG. 2 , the last roller pair  10  keeps the long sheet hanging from the fixed tray  11 . The long sheet is kept nipped in the machine body  2   a.    
     In Act  9 B, the finisher control unit  13  causes the finisher panel  19  to display “please remove the sheet”. 
     Since the sheet conveying path motor  6   c  and the motor  10   c  are stopped, the leading end of the long sheet keeps pushing up the distal end of the actuator  12   b.    
     In the case of the standard size sheet, the finisher control unit  13  detects that the sensor output of the fixed tray sheet sensor  12  changes when both the operation of the inlet roller pair  6  and the operation of the last roller pair  10  are off. 
     In the case of the long sheet, the finisher control unit  13  detects that the fixed tray sheet sensor  12  continues to be on when both the operation of the input roller pair  6  and the operation of the last roller pair  10  are off. 
     In Act B 10 , the finisher  2  notifies the MFP  1  that the long sheet is nipped. The MFP  1  stops the print job and the finisher  2  stops the job. 
     In Act B 11 , the user depresses the confirmation button  28  of the finisher panel  19 . The user removes the long sheet from the fixed tray  11 . The long sheet is removed from the fixed tray  11 . The sensor output of the fixed tray sheet sensor  12  changes from ON to OFF. 
     When the finisher control unit  13  detects the operation of the confirmation button  28 , the finisher control unit  13  stops the display of the finisher panel  19 . 
     In Act B 12 , the finisher control unit  13  determines whether the sensor output of the fixed tray sheet sensor  12  changes from ON to OFF. If the sensor output changes to OFF, through the YES route, the finisher control unit  13  ends the processing. 
     When the sensor output changes to OFF, the finisher  2  transmits a message of restoration to the MFP  1 . The MFP  1  executes another print job. 
     If the sensor output of the fixed tray sheet sensor  12  continues to be on in Act B 12 , through the NO route, the finisher control unit  13  stands by for the next image forming process (Act B 10 ). 
     The finisher  2  can hold the long sheet without along fixed tray for long sheet stacking or another paper discharge tray provided therein. The finisher  2  can hold the long sheet without an occupied area of the machine body  2   a  increased and apparatus height increased. Therefore, the problem in setting the finisher  2  is solved. 
     In the sheet post-processing apparatus according to the related art, it is difficult to stack the long sheet on the fixed tray or the movable tray without bending the long sheet and without scratching the long sheet. 
     In the sheet post-processing apparatus according to the related art, it is necessary to provide a dedicated component in order to stack the long sheet on the fixed tray without bending the long sheet and without scratching the long sheet. 
     A method of outputting a printed long sheet without bending the long sheet and without scratching the long sheet is attained by using the finisher  2  having a structural shape and size equivalent to a structural shape and size of the existing finisher. 
     (Modification of the First Embodiment) 
     The control panel  36  on the MFP  1  side may display indication that the control panel  36  urges the user to remove the long sheet. 
     As a modification of the example shown in  FIG. 7 , in Act B 9 , the finisher control unit  13  notifies the MFP control unit  35  that the long sheet is nipped. The MFP control unit  35  causes the control panel  36  to display “please remove the sheet”. 
     As a modification of  FIGS. 6A and 6B , in Act A 9 , if the sensor output of the fixed tray sheet sensor  12  continues to be on, through the NO route, in Act A 10 , the finisher control unit  13  notifies the MFP control unit  35  that the long sheet is nipped. The MFP control unit  35  causes the control panel  36  to display “fixed tray sheet stack FULL”. 
     Since the MFP  1  is caused to execute the display function, it is easy to let the user notice that the long sheet is nipped. 
     It is also possible to implement, in the MFP control unit  35  of the MFP  1 , application software for notifying, through a LAN connected to the MFP  1 , a personal computer or a mobile terminal that sheets are fully stacked. This enables the notification reliable. 
     (Second Embodiment) 
     In the first embodiment, the MFP  1  fixes the long sheet with the nip force of the last roller pair  10  of the finisher  2 . When a printed sheet is taken out, drawing force larger than the nip force is necessary. Therefore, the user consumes labor and time to draw out the sheet. The printed sheet is damaged. 
     In a second embodiment, the finisher  2  includes a nip-force releasing mechanism (a releasing mechanism). The nip-force releasing mechanism releases the nip force of the last roller pair  10  to take out the long sheet. 
     An image forming apparatus according to the second embodiment is also the MFP  1 . A sheet post-processing apparatus according to the second embodiment is also a finisher coupled to the MFP  1 . A nip-force releasing mechanism provided in the finisher is a manual mechanism. 
     A sheet post-processing method according to the second embodiment is also a method with which the finisher conveys the long sheet when the MFP applies printing to the long sheet. 
       FIG. 8  is an enlarged diagram of a main part of the finisher. Reference numerals and signs same as those described above denote the same components. 
     The MFP  1  and a finisher  200  are connected. A state in which the last roller pair  10  nips the long sheet and a state in which the last roller pair  10  releases the nip are shown in the figure. 
     As shown in  FIGS. 1 and 8 , the finisher  200  is configured by providing a nip releasing mechanism  52  in the finisher  2 . The nip releasing mechanism  52  is fixed to the machine body  2   a.    
     As an example, the nip releasing mechanism  52  includes a release lever  53  and a knob  54 . A lower end of the release lever  53  is axially supported by a frame in the machine body  2   a.    
     In a shaft body of the release lever  53 , a section that comes into contact with the upper roller  10   a  moves the upper roller  10   a  to a nip position and a release position. The nip releasing mechanism  52  releases nip force generated by the upper roller  10   a  and the lower roller  10   b.    
     The upper roller  10   a  is provided to be movable with respect to the machine body  2   a . The upper roller  10   a  is located in the nip position where the upper roller  10   a  comes into contact with the lower roller  10   b  and the release position where the upper roller  10   a  separates from the lower roller  10   b . The position of the lower roller  10   b  is fixed. 
     The upper roller  10   a  is applied with force for urging the upper roller  10   a  toward the lower roller  10   b . A spring or a leaf spring generates the force. 
     The last roller pair  10  discharges the long sheet and the standard size sheet to the fixed tray  11 . 
     After the sheet inlet sensor  8  detects the leading end of the long sheet, the inlet roller pair  6  and the last roller pair  10  convey the long sheet by a specified number of pulses in synchronization with each other. 
     Alternatively, the finisher control unit  13  stops only the inlet roller pair  6 . Alternatively, the finisher control unit  13  interrupts conveying force applied to the long sheet by the motor  10   c.    
     Thereafter, the inlet roller pair  6  and the last roller pair  10  stop. The last roller pair  10  in a halt nips the long sheet. The release lever  53  releases the nip force of the last roller pair  10 . 
       FIG. 9A  is a first flowchart for explaining a post-processing method for the standard size sheet of the finisher  200 .  FIG. 9B  is a second flowchart following  FIG. 9A . 
     In the MFP  1 , standard size sheets are set in the manual feed tray  37  or any one of the trays of the paper feeding unit  34  (Act C 1 ). 
     The MFP  1  selectively displays a type of a sheet different from the long sheet and the display panel  38  urges a user to start printing (Act C 2 ). 
     An original document is inserted into the scanner unit  31  and the MFP  1  starts execution of a print job (Act C 3 ). 
     The MFP  1  notifies the finisher  200  that a sheet is output (Act C 4 ). The finisher  200  causes the inlet roller pair  6 , the directing member  7 , and the last roller pair  10  to start to operate. 
     The MFP  1  discharges the standard size sheet (Act C 5 ). 
     The finisher control unit  13  detects that the sheet conveying path motor  6   c  is operating and that both the sheet inlet sensor  8  and the fixed tray sheet sensor  12  are on (Act C 6 ). 
     The finisher control unit  13  determines whether a sensor output of the sheet inlet sensor  8  changes from ON to OFF (Act C 7 ). While the sensor output does not change, the finisher control unit  13  repeats the processing in Act C 6  (the NO route in Act C 7 ). 
     If the sensor output changes from ON to OFF (the YES route in Act C 7 ), in Act C 8  in  FIG. 9B  (see a section marked B), the finisher  200  discharges the sheet to the fixed tray  11 . The finisher  200  continues to perform the discharge processing. 
     The finisher control unit  13  monitors whether the sensor output of the fixed tray sheet sensor  12  changes from ON to OFF (Act C 9 ). While the change is repeated, the finisher  200  continues the discharge of the sheet (the YES route in Act C 9 ). 
     If the sensor output of the fixed tray sheet sensor  12  continues to indicate ON (the NO route in Act C 9 ), the finisher control unit  13  causes the finisher panel  19  to display “fixed tray sheet stack FULL” (Act  010 ). 
     The finisher control unit  13  stops the job of the finisher  200  (Act C 11 ). The finisher  200  notifies the MFP  1  that the job is stopped, whereby the MFP  1  stops the execution of the print job (Act C 11 ). 
     The user grasps the leading end of the standard size sheet. The user pushes up the release lever  53  of the nip releasing mechanism  52  provided in the last roller pair  10  near the fixed tray  11 . The release lever  53  rotates with respect to the shaft of the lower roller  10   b . The nip force is released. The position of the fixed tray sheet sensor  12  returns to the original position. 
     The finisher control unit  13  detects, on the basis of an output of the fixed tray sheet sensor  12 , that a bundle of sheets is removed (Act C 12 ). 
     The finisher control unit  13  determines whether the sensor output of the fixed tray sheet sensor  12  changes from ON to OFF (Act C 13 ). 
     If the sensor output changes to OFF, in Act C 13 , though the YES route (see a section marked II), the MFP  1  executes a print job (Act C 3  in  FIG. 9A ). 
     If the sensor output does not change to OFF (the NO route in Act C 13  in  FIG. 9B ), the finisher control unit  13  ends the processing. 
     In  FIGS. 9A and 9B , when a processing request includes an instruction for stapling, the finisher  200  staples pages. 
     A control method with which the finisher  200  discharges the long sheet from the MFP  1  to the fixed tray  11  is explained below with reference to  FIG. 10 . 
       FIG. 10  is a flowchart for explaining a post-processing method for the long sheet of the finisher  200 . 
     In the MFP  1 , long sheets are set in the manual feed tray  37  (Act D 1 ). 
     The MFP  1  selectively displays the long sheet. The display panel  38  urges the user to start printing (Act D 2 ). 
     The MFP  1  starts execution of a print job (Act D 3 ). The scanner unit  31  reads an original document or the MFP control unit  35  captures image data through a LAN, whereby the MFP  1  forms an image on the long sheet. 
     The MFP  1  notifies the finisher  2  of a processing request for designating the output of the long sheet and the fixed tray  11  (Act D 4 ). The processing request may include the size of the long sheet. 
     The MFP  1  discharges the long sheet (Act D 5 ). 
     The finisher control unit  13  causes the sheet conveying path motor  6   c  to start driving before a predetermined time elapses. The finisher control unit  13  causes the directing member  7  to close the lower conveying path. The finisher control unit  13  causes the motor  10   c  to start driving. 
     The finisher control unit  13  receives the input of ON from the sheet inlet sensor  8 . Thereafter, the finisher control unit  13  receives the input of ON from the fixed tray sheet sensor  12 . 
     The finisher control unit  13  detects that the sheet conveying path motor  6   c  is operating and both the sheet inlet sensor  8  and the fixed tray sheet sensor  12  are on (Act D 6 ). 
     The finisher control unit  13  determines whether the sensor output of the sheet inlet sensor  8  changes from ON to OFF (Act D 7 ). While the sensor output does not change (the NO route in Act D 7 ), the finisher control unit  13  continues to detect the long sheet. 
     If the sensor output changes from ON to OFF (the YES route in Act D 7 ), the finisher control unit  13  causes the sheet conveying path motor  6   c  to operate by a specified number of pulses and stops the motor driving (Act D 8 ). 
     The finisher control unit  13  causes the motor  10   c  to operate by the specified number of pulses in synchronization with the rotation of the sheet conveying path motor  6   c . Alternatively, the finisher control unit  13  stops only the motor  10   c  or interrupts conveying force applied to the long sheet by the motor  10   c.    
     The finisher control unit  13  stops the motor driving for the last roller pair  10  and, at the same time, causes the last roller pair  10  to nip the trailing end of the long sheet. A state of the long sheet is changed to a state in which the long sheet is nipped by the last roller pair  10 . 
     The finisher control unit  13  causes the LED  28  to display “please remove the sheet” (Act D 9 ). 
     Since the sheet conveying path motor  6   c  and the motor  10   c  are stopped, the leading end of the long sheet keeps pushing up the distal end of the actuator  12   b.    
     The MFP  1  stops the print job and the finisher  200  stops the job (Act D 10 ). 
     The user pushes up the release lever  53  while grasping the leading end of the long sheet. The nip force is released. The position of the fixed tray sheet sensor  12  returns to the original position. 
     The finisher control unit  13  detects, on the basis of an output of the fixed tray sheet sensor  12 , that the long sheet is removed (Act D 11 ). The finisher control unit  13  stops the display of the finisher panel  19 . 
     The finisher control unit  13  determines whether the sensor output of the fixed tray sheet sensor  12  changes from ON to OFF (Act D 12 ). If the sensor output changes to OFF (the YES route), the finisher control unit  13  ends the processing. 
     If the sensor output of the fixed tray sheet sensor  12  continues to be on (the NO route in Act D 12 ), the finisher control unit  13  stands by for the next image forming process (Act D 10 ). 
     When the finisher  200  receives and discharges the long sheet output from the MFP  1 , the last roller pair  10  nips the long sheet. When the user takes out the long sheet, the release lever  53  releases the nip force generated by the last roller pair  10 . Therefore, it is possible to perform printing without bending the long sheet and without scratching the long sheet. 
     The finisher  200  can hold the long sheet without an occupied area of the machine body  2   a  and apparatus height increased. 
     Therefore, it is possible to handle the long sheet without providing a dedicated component in the sheet post-processing apparatus according to the related art. A high function can be imparted to the finisher  200  by attaching the nip releasing mechanism  52  to the sheet post-processing apparatus according to the related art and rewriting the ROM. 
     In the first embodiment, when the last roller pair  10  nips the long sheet, if the user pulls out the long sheet, it is likely that the last roller pair  10  steps out. With the finisher  200 , it is possible to remove the long sheet without causing the step-out. 
     (Modification of the Second Embodiment) 
     The control panel  36  on the MFP  1  side may display indication that the control panel  36  urges the user to remove the long sheet. 
     In Act D 9  in  FIG. 10 , the finisher control unit  13  notifies the MFP control unit  35  that the long sheet is nipped. The MFP control unit  35  causes the control panel  36  to display “please remove the sheet”. Therefore, it is easy to let the user to notice that the long sheet is nipped. 
     If the senor output of the fixed tray sheet sensor  12  continues to be on in Act C 9  in  FIG. 9B , through the NO route, in Act C 10 , the finisher control unit  13  notifies the MFP control unit  35  that the long sheet is nipped. The MFP control unit  35  causes the control panel  36  to display “fixed tray sheet stack FULL”. 
     It is also possible to implement, in the MFP control unit  35  of the MFP  1 , application software for notifying, through a LAN connected to the MFP  1 , a personal computer or a mobile terminal that sheets are fully stacked. 
     (Third Embodiment) 
     A puncher unit and a unit configured to divide a conveying path may be provided between the sheet post-processing apparatus and the MFP  1 . 
       FIG. 11  is an enlarged diagram of a main part of a sheet post-processing apparatus according to a third embodiment. Reference numerals and signs same as those described to above denote the same components. 
     A sheet post-processing apparatus  300  conveys a sheet to a unit on a side on which the stapler  17  is mounted or a saddle unit  55  and performs post-processing. The saddle unit  55  performs post-processing such as saddle stapling and saddle folding for pages. 
     The sheet post-processing apparatus  300  includes a puncher unit  56  configured to punch the sheet. The sheet post-processing apparatus  30  includes a sheet directing unit  57  configured to direct the sheet to the saddle unit  55  side or the fixed tray  11  side. 
     The sheet directing unit  57  includes a directing member  58 , an upper sheet conveying path  59  to the fixed tray  11 , and a lower sheet conveying path  60  to the saddle unit  55 . 
     The sheets are supplied to the inlet roller pair  6  as the first roller pair from the sheet directing unit  57 . 
     With such a configuration, the MFP  1  prints the long sheet. The puncher unit  56  punches the long sheet. 
     It is possible to perform printing, punching, saddle stapling, and the like without bending the long sheet and without scratching the long sheet. The release lever  53  may be provided in the sheet post-processing apparatus  300  to release nip force. 
     The finisher panel  19  or the control panel  36  may display FULL. 
     (Other Embodiments) 
     An image forming apparatus according to an embodiment may be a monochrome copying machine, a printer, or a facsimile. 
     The structure of the fixed sensor sheet sensor  12  shown in  FIG. 4  can be variously changed. The superiority of the embodiments is not spoiled at all with respect to embodiments merely carried out by changing the structure of the fixed tray sheet sensor  12 . 
     As specific examples of the standard sizes, the ISO A3 size is width 297 mm×length 420 mm and the A4 size is width 210 mm×length 297 mm. The LD size for the North America is width 432 mm×length 279 mm, the tabloid size is width 279 mm×length 432 mm, the LG size is width 216 mm×length 356 mm, and the LT size is width 216 mm×length 279 mm. 
     When the tray length of the fixed tray  11  is adjusted to the sheet length of the A4 size, A4, LD, and LT sheets do not fall from the fixed tray  11 . 
     The sheet lengths of A3, tabloid, and LG sheets are larger than the tray length of the fixed tray  11 . After the sheets are conveyed to the fixed tray  11 , the sheets fall onto the floor surface from the fixed tray  11 . 
     With the finishers  2 ,  200 , and  300 , it is possible to output, for example, a long sheet having length several times as large as the sheet length of the A4 size without dropping the long sheet onto the floor surface. 
     The finishers may execute, on the A3, tabloid, and LG sheets, processing same as the processing for the long sheet. 
     The sensor  12   d  may be a micro switch instead of the photointerrupter. The micro switch has an energized fixed contact. A movable contact is provided in the piece member  12   c , whereby the sensor  12   d  detects on and off between the fixed contact and the movable contact. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and apparatus described herein may be embodied in a variety of other forms; furthermore various omissions and substitutions and changes in the form of methods and systems described herein may be made without departing from the sprit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and sprits of the inventions.