Patent Publication Number: US-7588241-B2

Title: Sheet processing apparatus, sheet processing method, image forming apparatus, program for implementing the method, and storage medium storing the program

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to controlling the insertion of sheets into a bundle of stacked sheets with images formed thereon. 
   2. Description of the Related Art 
   Some conventional copying apparatuses which are image forming apparatuses have a function of inserting a sheet (hereinafter referred to as “special sheet”) different from a plain sheet to the first page, last page, or middle page of sheets. This function is referred to as a cover mode, an interleaving sheet mode, and so forth according to the page to which the special sheet is inserted. The user sets any of these modes through an operating section provided in such copying apparatuses. For example, a special sheet such as a sheet different in color from a plain sheet, a color copy sheet, or the like can be inserted as a cover sheet, and special sheets can be inserted as dividers between plain sheets every predetermined number of sheets (see U.S. Pat. No. 6,353,726). 
   Examples of methods to supply special sheets include a method in which special sheets are supplied from a cassette for use in supplying special sheets. Also, there has been proposed a method in which special sheets are supplied from a sheet feeder provided in a sheet processing apparatus such as a finisher which carries out postprocessing on sheets with images formed thereon output from a copying apparatus. 
   Also, there has been proposed a postprocessing method in which postprocessing such as stapling and punching is carried out on special sheets supplied from the above-mentioned sheet feeder. 
   In the case where the finisher carries out the above-mentioned postprocessing, a special sheet supplied from the sheet feeder or the cassette is inverted in a predetermined direction and laid over a sheet output from the copying apparatus. 
   The copying apparatus and the finisher are constructed in consideration of cases where various special sheets (such as a 300 g/m 2  sheet which is very thick) are conveyed. 
   The conventional copying apparatus and finisher, however, have to be large-sized because the curve of an inversion path which inverts special sheets needs to be gentle so as to prevent buckling and jamming of special sheets. 
   When jamming of a special sheet occurs, the user has to prepare the same special sheet again, which is troublesome for the user and causes cost increase. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a sheet processing apparatus and a sheet processing method which can reduce the size of the apparatus and suppress cost increase by preventing sheet buckling and jamming, an image forming apparatus, a program for implementing the method, and a storage medium storing the program. 
   To attain the above object, in a first aspect of the present invention, there is provided a sheet processing apparatus connected to an image forming apparatus that forms images corresponding to a set operation mode on sheets, comprising a first stacking section that stacks sheets, a curved inversion path that inverts the sheets, a sheet feed section that feeds the sheets stacked in the first stacking section in one of a first sheet feed mode in which sheets are fed after being inverted by the inversion path and a second sheet feed mode in which sheets are fed without passing through the inversion path, a conveying section that conveys the sheets fed by the sheet feed section and the sheets with the images formed thereon, a second stacking section that stacks the conveyed sheets, a sheet processing section that performs predetermined processing on the sheets stacked in the second stacking section, a setting section that sets sheet information about the sheets stacked in the first stacking section, a determining section that determines whether a predetermined information is included in the set sheet information, and a display section that displays a predetermined message when the predetermined information is included in the set sheet information. 
   Preferably, the sheet processing apparatus according comprises an inhibiting section that inhibits the inversion of the sheets by the inversion path when the predetermined information is included in the set sheet information. 
   Preferably, the predetermined information comprises information indicative of a special type sheet. 
   Preferably, the predetermined message comprises a message notifying a user that the inversion of the sheets by the inversion path has been inhibited. 
   Preferably, the predetermined message comprises a message prompting a user to confirm an orientation of the sheets stacked in the first stacking section 
   Preferably, the predetermined message comprises a message prompting a user to change an orientation of the sheets stacked in the first stacking section. 
   To attain the above object, in a second aspect of the present invention, there is provided a sheet processing method for controlling a sheet processing apparatus connected to an image forming apparatus that forms images corresponding to a set operation mode on sheets, the sheet processing apparatus comprising a first stacking section that stacks sheets, a curved inversion path that inverts the sheets, a sheet feed section that feeds the sheets stacked in the first stacking section in one of a first sheet feed mode in which sheets are fed after being inverted by the inversion path and a second sheet feed mode in which sheets are fed without passing through the inversion path, a conveying section that conveys the sheets fed by the sheet feed section and the sheets with the images formed thereon, a second stacking section that stacks the conveyed sheets, and a sheet processing section that performs predetermined processing on the sheets stacked in the second stacking section, the method comprising a setting step of setting sheet information about the sheets stacked in the first stacking section, a determining step of determining whether a predetermined information is included in the set sheet information, and a display step of displaying a predetermined message when the predetermined information is included in the set sheet information. 
   Preferably, the sheet processing method comprises an inhibiting step of inhibiting the inversion of the sheets by the inversion path when the predetermined information is included in the set sheet information. 
   Preferably, the predetermined information comprises information indicative of a special type sheet. 
   Preferably, the predetermined message comprises a message notifying a user that the inversion of the sheets by the inversion path has been inhibited. 
   Preferably, the predetermined message comprises a message prompting a user to confirm an orientation of the sheets stacked in the first stacking section. 
   Preferably, the predetermined message comprises a message prompting a user to change an orientation of the sheets stacked in the first stacking section. 
   To attain the above object, in a third aspect of the present invention, there is provided an image forming apparatus comprising an image forming section that forms images on sheets, a first stacking section that stacks sheets, a curved inversion path that inverts the sheets, a sheet feed section that feeds the sheets stacked in the first stacking section in one of a first sheet feed mode in which sheets are fed after being inverted by the inversion path and a second sheet feed mode in which sheets are fed without passing through the inversion path, a conveying section that conveys the sheets fed by the sheet feed section and the sheets with the images formed thereon, a second stacking section that stacks the conveyed sheets, a sheet processing section that performs predetermined processing on the sheets stacked in the second stacking section, a setting section that sets sheet information about the sheets stacked in the first stacking section, a determining section that determines whether a predetermined information is included in the set sheet information, and a display section that displays a predetermined message when the predetermined information is included in the set sheet information. 
   To attain the above object, in a fourth aspect of the present invention, there is provided a program for causing a computer to execute a sheet processing method for controlling a sheet processing apparatus connected to an image forming apparatus that forms images corresponding to a set operation mode on sheets, the sheet processing apparatus comprising a first stacking section that stacks sheets, a curved inversion path that inverts the sheets, a sheet feed section that feeds the sheets stacked in the first stacking section in one of a first sheet feed mode in which sheets are fed after being inverted by the inversion path and a second sheet feed mode in which sheets are fed without passing through the inversion path, a conveying section that conveys the sheets fed by the sheet feed section and the sheets with the images formed thereon, a second stacking section that stacks the conveyed sheets, and a sheet processing section that performs predetermined processing on the sheets stacked in the second stacking section, the program comprising a setting module for setting sheet information about the sheets stacked in the first stacking section, a determining module for determining whether a predetermined information is included in the set sheet information, and a display module for displaying a predetermined message when the predetermined information is included in the set sheet information. 
   To attain the above object, in a fifth aspect of the present invention, there is provided a computer-readable storage medium storing a program according to the fourth aspect of the invention. 
   According to the present invention, sheet information about sheets stacked on the first stacking section is set, and if predetermined information is included in the set sheet information, a predetermined message is displayed. Thus, it is possible to make the apparatus compact and suppress cost increase by preventing sheet buckling and jamming. 
   The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view schematically showing the internal construction of a copying system according to an embodiment of the present invention. 
       FIGS. 2A and 2B  are views useful in explaining a fixed original reading method and a moving original reading method executed by a scanner unit appearing in  FIG. 1 . 
       FIG. 3  is a block diagram schematically showing the construction of a copying apparatus appearing in  FIG. 1 . 
       FIG. 4  is a block diagram schematically showing the construction of an image signal controller appearing in  FIG. 3 . 
       FIG. 5  is a sectional view schematically showing the constructions of a folding processing section, a finisher, and an inserter appearing in  FIG. 1 . 
       FIG. 6  is a block diagram schematically showing the construction of the finisher appearing in  FIG. 3 . 
       FIG. 7A  is a view showing an example of a postprocessing selection menu screen displayed on a display panel of an operating unit of the copying apparatus appearing in  FIG. 1 , and  FIG. 7B  is a view showing an example of a cover designation menu screen displayed on the display panel of the operating unit. 
       FIG. 8A  is a view showing a direction in which sheets stacked on an insert tray appearing in  FIG. 5  are conveyed, and  FIG. 5B  is a view showing a state in which sheets are stacked on the insert tray of the inserter. 
       FIG. 9  is a view useful in explaining a sheet C 1  guided to a conveying path in the finisher appearing in  FIG. 8 . 
       FIG. 10  is a view useful in explaining a sheet P 1  conveyed to the finisher appearing in  FIG. 8 . 
       FIG. 11  is a view useful in explaining the sheet C 1  conveyed to a processing tray of the finisher appearing in  FIG. 8 . 
       FIG. 12A  is a view showing a sheet bundle stacked on the processing tray appearing in  FIG. 5 ,  FIG. 12B  is a view showing a sheet bundle of which front cover is the sheet C 1 , and  FIG. 12C  is a view showing a sheet bundle of which back cover is a sheet C 2 . 
       FIG. 13  is a view useful in explaining an image forming process carried out by a printer section appearing in  FIG. 1  in the case where a bookbinding mode is set as an operation mode. 
       FIG. 14  is a view useful in explaining a bookbinding process carried out by the finisher appearing in  FIG. 1  in the case where the bookbinding mode is set as the operation mode. 
       FIG. 15A  is a view showing a direction in which a sheet for use as a front cover is conveyed in the bookbinding process carried out by the finisher appearing in  FIG. 1 , and  FIG. 15B  is a view showing a state in which sheets for use as front covers are stacked on the insert tray in the bookbinding process. 
       FIG. 16A  is a view showing a state in which a sheet for use as a front cover has been conveyed to the inversion path in the bookbinding process carried out by the finisher appearing in  FIG. 1 , and  FIG. 16B  is a view showing a state in which the sheet for use as the front cover inverted in the bookbinding process has been conveyed into the finisher. 
       FIG. 17A  is a view showing the state of the sheet for use as the front cover guided into a first bookbinding path in the bookbinding process carried out by the finisher appearing in  FIG. 1 , and  FIG. 17B  is a view showing the state of the sheet for use as the front cover conveyed into a housing guide in the bookbinding process. 
       FIG. 18A  is a view showing a state in which a sheet P 1  has been conveyed in the bookbinding process carried out by the finisher appearing in  FIG. 1 , and  FIG. 18B  is a view showing a state in which a sheet P 2  has been conveyed in the bookbinding process. 
       FIG. 19  is a view useful in explaining how an inappropriate sheet is discharged onto a sample tray in the finisher appearing in  FIG. 5 . 
       FIG. 20  is a flow chart showing the procedure of an operation mode determining process carried out by a finisher controller appearing in  FIG. 6 . 
       FIG. 21  is a flow chart showing the procedure of an inserter sheet pre-feed process in a step S 1904  in  FIG. 20 . 
       FIG. 22  is a flow chart showing the procedure of a bookbinding process in a step S 1907  in  FIG. 20 . 
       FIG. 23  is a flow chart showing the procedure of an inserter sheet feed process in a step S 2108  in  FIG. 22 . 
       FIG. 24  is a flow chart showing the procedure of a skew detecting process in a step S 2006  in  FIG. 21 . 
       FIG. 25  is a flow chart showing the procedure of a sheet information setting process for sheets stacked on the insert tray appearing in  FIG. 5 . 
       FIG. 26  is a view useful in explaining a “sheet size selection screen” displayed on the display panel in a step S 2403  in  FIG. 25 . 
       FIG. 27  is a view useful in explaining a “sheet type selection screen” displayed on the display panel in a step S 2407  in  FIG. 25 . 
       FIG. 28  is a view useful in explaining a screen displayed on the display panel in a step S 2423  in  FIG. 25 . 
       FIG. 29  is a view useful in explaining a screen displayed on the display panel in a step S 2422  in  FIG. 25 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described in detail with reference to the drawings showing a preferred embodiment thereof. 
     FIG. 1  is a sectional view schematically showing the internal construction of a copying system according to an embodiment of the present invention. 
   As shown in  FIG. 1 , the copying system  2000  is comprised of a copying apparatus  1000 , a folding processing section  400 , a finisher  500 , and an inserter  900 . The copying apparatus  1000  is comprised of an image reader section  200  and a printer section  300 . 
   An image feeding section  100  is comprised of a tray  1001  on which originals are stacked. Originals stacked on the tray  1001  are sequentially conveyed one by one from the first page toward the left as viewed in  FIG. 1 . It should be noted that originals are placed on the tray  1001  in an erected image as viewed from the user and with surfaces thereof on which images are formed facing upward (hereinafter referred to as “the face-up state”). 
   The original feeder  100  is provided with a discharged sheet tray  112  onto which the originals conveyed as mentioned above are discharged after being conveyed from left to right as viewed in  FIG. 1  on a platen glass  102 , described later, via a curved path. 
   The image reader section  200  is comprised of the platen glass  102  on which an original is placed, and a scanner unit  104  provided on a bottom of the platen glass  102 . 
   The scanner unit  104  is comprised of a lamp  103 , mirrors  105 ,  106 , and  107 , a lens  108 , and an image sensor  109 . The lamp  103  illuminates an original being conveyed. The mirrors  105 ,  106 , and  107  guide reflected light from the illuminated original. The lens  108  guides the reflected light guided by the mirrors  105  to  107  to the image sensor  109 . The image sensor  109  carries out photoelectric conversion of the incident reflected light through the lens  108  and outputs image data of the original. 
   Methods to read image data of an original using the scanner unit  104  include a moving original reading method and a fixed original reading method. In the moving original reading method, an image on an original is read while the original is conveyed from left to right as viewed in  FIG. 1  on the platen glass  102  with the scanner unit  104  being held at a predetermined position. In the fixed original reading method, an image on an original is read while the scanner unit  104  is moved from left to right as viewed in  FIG. 1  with the original being held on the platen glass  102 . 
   In the fixed original reading method, the original feeder  100  may convey an original onto the platen glass  102 , or alternatively, the user may lift the original feeder  100  and place an original on the platen glass  102  without using the original feeder  100 . 
   The printer section  300  is provided with an exposure controller  110 , a polygon mirror  110   a , a photosensitive drum  111 , and a developing unit  113 . The exposure controller  110  receives image data output by the image sensor  109 , carries out predetermined image processing on the received image data, and outputs the resulting image data as a laser beam. The polygon mirror  110   a  reflects the output laser beam while rotating and scans the photosensitive drum  111 . The developing unit  113  develops and visualizes an electrostatic latent image formed on the photosensitive drum  111  by scanning as a toner image. 
   The printer section  300  is provided with cassettes  114  and  115  on which sheets are stacked, a manual sheet feed section  125 , a double-sided conveying path  124 , a transfer section  116 , and a fixing section  117 . The transfer section  116  transfers a toner image visualized as mentioned above onto conveyed sheets. The fixing section  117  fixes transferred toner images onto sheets. 
   The printer section  300  is further provided with a flapper  121 , a pair of discharge rollers  118 , and a conveying path  122 . The flapper  121  switches the destination of a sheet to one of the folding processing section  400  and the double-sided conveying path  124 . The discharge rollers  118  convey a sheet toward the folding processing section  400 . 
   The conveying direction of a sheet conveyed to the path  122  by a switching action of the flapper  121  is reversed (switched back) after the trailing end of the sheet leaves the flapper  121 , and the sheet is then conveyed to the discharge rollers  118  by a switching action of the flapper  121 . The sheet is discharged from the printer section  300  by the discharge rollers  118  and conveyed to the folding processing section  400 . In this way, the printer section  300  can discharge a sheet with a toner image formed thereon to the folding processing section  400  with a surface thereof on which the toner image has been formed facing downward (hereinafter referred to as “the face-down state”). This will hereafter be referred to as “inverted discharge (face-down discharge).” 
   By discharging sheets in the face-down state from the printer section  300  as described above, sheets with images formed thereon can be collated in the case where image formation is sequentially carried out on the first to last pages in this order. The cases where image formation is sequentially carried out on the first to last pages in this order include, for example, the case where image formation is carried out on image data of originals read by the original feeder  100  and the case where image formation is carried out on image data input from a computer. 
   In carrying out image formation on a hard sheet such as an OHP sheet fed from the manual sheet feed section  125 , the printer section  300  discharges the OHP sheet in the face-up state to the folding processing section  400  without passing it through the path  122 . 
   On the other hand, in carrying out image formation on both sides of a sheet, the sheet is conveyed directly from the fixing section  117  toward the discharging rollers  118 . The sheet is switched back after the trailing end of the sheet leaves the flapper  121 , and the sheet is then conveyed to the double-sided conveying path  124  by a switching action of the flapper  121 . 
   The folding processing section  400  carries out a folding process in which a sheet is folded in a Z-shape. 
   In the case where a large size such as an A4- or B4-size has been set as the sheet size and the folding processing section  400  has been set to carry out the folding process through an operating unit  1  of the copying apparatus  1000 , the folding processing section  400  carries out the folding process on a sheet discharged from the printer section  300 . In the case where the folding processing section  400  has not been set to carry out the folding process, the folding processing section  400  conveys the sheet directly to the finisher  500  without carrying out the folding process. 
   The inserter  900  is provided at a top of the finisher  500 , for inserting a sheet such as an interleaved sheet or a cover sheet different from an ordinary sheet to any of the first page, last page, and middle page of each of a plurality of sheet bundles on which images have been formed by the printer section  300 . 
   The finisher  500  carries out various processes such as a binding process, a staling process, and a hole-punching process (hereinafter referred to as “the punching process”) on a sheet bundle including sheets conveyed from the printer section  300  via the folding processing section  400  and sheets conveyed from the inserter  900 . 
     FIGS. 2A and 2B  are views useful in explaining the fixed original reading method and the moving original reading method executed by the scanner unit  104  appearing in  FIG. 1 . 
   As shown in  FIG. 2A , in the fixed original reading method, the scanner unit  104  carries out scanning-in of an image on an original held on the platen glass  102  in a main scanning direction Sy and a sub-scanning direction Sx ((A- 1 ) in  FIG. 2A ). The image read by the image sensor  109  ((A- 2 ) in  FIG. 2A ) is sequentially converted into laser light by the exposure controller  110 . The polygon mirror  110   a  causes the laser light to scan the photosensitive drum  111  in a direction indicated by an arrow in  FIG. 2A . As a result, an electrostatic latent image is formed on the photosensitive drum  111  ((A- 3 ) in  FIG. 2A ) The electrostatic latent image formed on the photosensitive drum  111  is developed by toners and transferred onto a sheet. 
   In the moving original reading method, the scanner unit  104  carries out scanning-in of an image on an original being conveyed from left to right on the platen glass  102  as viewed in  FIG. 1  in a main scanning direction Sy and a sub-scanning direction Sx ((B- 1 ) in  FIG. 2B ). The image read by the image sensor  109  ((A- 2 ) in  FIG. 2A ) is sub-scanned in a direction opposite to the direction in which an image is sub-scanned in the fixed original reading method ((B- 2 ) in  FIG. 2B ). Thus, the image read by the image sensor  109  is a mirror image of the original image and therefore has to be corrected to a normal mage on a line-by-line basis. 
   Accordingly, in the moving original reading method, a mirroring process in which the image read by the image sensor  109  is inverted on a line-by-line basis with respect to the main scanning direction thereof is carried out so as to convert the read image to a normal image. Thus, a normal image can be obtained by rotating the original image 180 degrees and carrying out the mirroring process on the read image (B- 3 ) in  FIG. 2B ). 
   Laser light is modulated by the exposure controller  110  based on the normal image obtained by the mirroring process and caused to scan the photosensitive drum  111  in a direction indicated by an arrow in  FIG. 2B . As a result, an electrostatic latent image is formed on the photosensitive drum  111  ((B- 4 ) in  FIG. 2B ). The electrostatic latent image formed on the photosensitive drum  111  is developed by toners and transferred onto a sheet. 
   The printer section  300  then inverts the sheet with the image has been fixed thereon and discharges the sheet with the image formed thereon in the face-down state to the folding processing section  400  ((B- 5 ) in  FIG. 2B ). 
   Next, a stapler  601 , described later, of the finisher  500  appearing in  FIG. 5  staples the inverted sheet at a trailing end thereof, i.e. on a left side of the surface on which the image is formed. 
   It should be noted that the mirroring process may be carried out by inverting a sheet with respect to the sub-scanning direction, but in this case, the mirroring process cannot be started unless reading of an image on one page of originals is completed. Also, since an image is not rotated 180 degrees when a sheet with the image formed thereon is inverted with respect to the sub-scanning direction, the sheet discharged in the face-down state is stapled at a trailing end thereof, i.e. a right end of a surface on which an image is formed. For this reason, the mirroring process in which sheets are inverted with respect to the main scanning direction is more preferable than the mirroring process in which sheets are inverted with respect to the sub-scanning direction. 
     FIG. 3  is a block diagram schematically showing the construction of the copying apparatus  1000  appearing in  FIG. 1 . 
   As shown in  FIG. 3 , the copying apparatus  1000  includes an original feeder controller  101 , an image reader controller  201 , a printer controller  301 , a folding processing controller  401 , a finisher controller  501 , a CPU circuit section  150 , and the operating section  1 . The CPU circuit section  150  sends and receives signals to and from the original feeder controller  101 , the image reader controller  201 , the printer controller  301 , the folding processing controller  401 , and the finisher controller  501 . 
   The copying apparatus  1000  also includes an external I/F  209  and an image signal controller  202 . The external I/F  209  receives signals from the CPU circuit section  150  and an external computer  210 . The image signal controller  202  receives signals from the image reader controller  201 , the CPU circuit section  150 , and the external I/F  209  and sends signals to the printer controller  301 . 
   The CPU circuit section  150  includes a CPU, not shown, a ROM  151  that stores control programs, and a RAM  152  that is used as an area for temporarily storing control data or a working area for computations associated with control. Based on the control programs and the signals from the operating section  1 , the CPU circuit section  150  controls the original feeder controller  101 , the image reader controller  201 , the image signal controller  202 , the printer controller  301 , the folding processing controller  401 , the finisher controller  501 , and the external I/F  209 . 
   The original feeder controller  101  controls the original feeder  100 , the image reader controller  201  controls the image reader section  200 , the printer controller  301  controls the printer section  300 , the folding processing controller  401  controls the folding processing section  400 , and the finisher controller  501  controls the finisher  500 . 
   The operating section  1  includes a plurality of keys for inputting setting information related to image formation, such as operation modes and sheet sizes, and a display panel. The operating section  1  sends inputted setting information to the CPU circuit section  150 . Further, the operating section  1  receives a signal sent from the CPU circuit section  150  and displays information corresponding to the received information, setting information, etc. on the display panel. 
   The external I/F  209  interfaces with the external computer  210 . The external I/F  209  expands print data sent from the computer  210  into a bitmap image and outputs the bitmap image in the form of image data to the image signal controller  202 . 
   The image reader controller  210  outputs image data of an original read by the image sensor  109  to the image signal controller  202 . 
   The printer controller  301  outputs image data output from the image signal controller  202  to the exposure controller  110 . 
     FIG. 4  is a block diagram schematically showing the construction of the image signal controller  202  appearing in  FIG. 3 . 
   In  FIG. 4 , reference numeral  203  denotes an image processor that carries out image correction processing required for image formation and carries out image editing processing according to an operation mode set through the operating section  1 ;  204 , a line memory; and  205 , a page memory. The image processor  203 , line memory  204 , and page memory  205  are connected in series. Reference numeral  206  denotes a hard disk that is used to, for example, store images and change page sequences, i.e. electronic sorting. 
   It should be noted that the line memory  204  is used for the above described mirroring process; images output from the line memory  204  are input to the printer controller  301  via the page memory  205 . 
     FIG. 5  is a sectional view schematically showing the constructions of the folding processing section  400 , the finisher  500 , and the inserter  900  appearing in  FIG. 1 . 
   In  FIG. 5 , reference numeral  402  denotes a conveying path that guides a sheet discharged from the printer section  300  to the finisher  500 . Reference numerals  403  and  404  each denote a pair of conveying rollers provided on the conveying path  402 . Reference numeral  420  denotes a folding path that is branched from the conveying path  402  between the conveying rollers  403  and  404 . 
   Reference numeral  410  denotes a switching flapper that switches the destination of a sheet to one of the finisher  500  and the folding path  420 . Reference numeral  421  denotes folding rollers provided on the folding path  420 . 
   In the case where the folding process is carried out, the switching flapper  410  switches the destination of a sheet to the folding path  420 . Thus, the sheet conveyed from the printer section  300  is conveyed to the folding rollers  421  via the folding path  420  and folded in a Z-shape. 
   In the case where the folding process is not carried out, the switching flapper  410  switches the destination of a sheet to the finisher  500 . As a result, the sheet conveyed from the printer section  300  is conveyed to the finisher  500  via the conveying path  402 . 
   The finisher  500  includes a path that guides a sheet conveyed from the printer section  300  via the folding processing section  400  and carries out postprocessing on the sheet. 
   Reference numeral  502  denotes a pair of inlet rollers that takes a sheet conveyed from the printer section  300  via the folding processing section  400  into the finisher  500 . Reference numeral  552  denotes a finisher path that guides a sheet conveyed from the inlet rollers  502 . Reference numeral  553  denotes a first bookbinding path branched from the finisher path  552 . Reference numeral  554  denotes a second bookbinding path  554  branched from the first bookbinding path  553  toward the finisher path  522  and connected to the finisher path  552 . Reference numeral  551  denotes a switching flapper that is provided at a location enclosed by the finisher path  552 , the first bookbinding path  553 , and the second bookbinding path  554  and selectively switches the destination of a sheet to any of the finisher path  552 , the first bookbinding path  553 , and the second bookbinding path  554 . 
   Reference numeral  503  denotes a pair of conveying rollers that are rotatable forward and backward and convey a sheet guided to a finisher path  552 . Reference numeral  505  denotes a buffer roller that is rotatable forward and backward and takes in a sheet conveyed by the conveying rollers  503 . Reference numeral  521  denotes a non-sort path  521  branched from the sort path  522 . Reference numeral  522  denotes a sort path that guides a sheet taken in by the buffer roller  505 . Reference numeral  510  denotes a switching flapper that separates a sheet wound on the buffer roller  505  from the buffer roller  505  and conveys the sheet to a non-sort path  521  (non-sort processing) or selects a path so as to convey the sheet directly to the sort path  522  without separating it from the buffer roller  505 . Reference numeral  509  denotes a pair of discharge rollers provided on the non-sort path  521 . Reference numeral  533  denotes a discharged sheet sensor provided between the switching flapper  510  and the pair of discharge rollers  509 , for detecting jamming or the like. Reference numeral  531  denotes an inlet sensor provided between the pair of inlet rollers  502  and the pair of conveying rollers  503 . A predetermined number of sheets conveyed from the conveying rollers  503  are wound on the buffer roller  505  by depressing rollers  512 ,  513 , and  514  provided on a rotating surface of the buffer roller  505  as the buffer roller  505  rotates. A sheet conveyed to the non-sort path  521  by the switching flapper  510  is discharged onto a sample tray  701  via the pair of discharge rollers  509 . 
   Reference numeral  506  and  507  denote a pair of conveying rollers and a pair of discharge rollers, respectively, that convey a sheet guided to the sort path  522  by the switching flapper  510 . Reference numeral  630  denotes an intermediate tray (hereinafter referred to as “the processing tray”) on which conveyed sheets are staked in the form of a bundle. A bundle of sheets on the processing tray  630  is aligned in the stacking direction thereof and stapled according to e.g. an operation mode set through the operating section  1 . Reference numeral  601  denotes the stapler that staples a group of sheets stacked in the form of a bundle on the processing tray  630 . Reference numerals  680   a  and  680   b  denote discharge rollers that convey a group of sheets having been aligned and stapled. Reference numeral  700  denotes a vertically free-running stack tray onto which a group of sheets having been conveyed is discharged. Reference numeral  550  denotes a punch unit including a punch roller comprised of a die section and a punch section. The punch unit  550  operates in accordance with e.g. an operation mode set through the operating section  1  and carries out the punching process in which a hole is punched in an area at the trailing end of a sheet conveyed from the inserter  900  or the printer section  300  via the conveying rollers  503 . 
   In punching a sheet, the punch unit  550  causes the punch roller to rotate 360 degrees when the trailing end of the sheet reaches the punch unit  550 , thereby making a punch hole at the trailing end of the sheet. It should be noted that in consideration of productivity and cost, the punching is carried out with respect to each sheet as the sheet is conveyed. 
   In the following description, a point of branch to the finisher path  552  and the second bookbinding path  554  will be referred to as “the branch A.” 
   A sheet conveyed from the inlet rollers  502  is conveyed toward the conveying rollers  503  by the switching flapper  551 . Thereafter, when the conveying rollers  503  are rotated backward, the sheet is conveyed toward the second bookbinding path  554  by the switching flapper  551 , not toward the inlet rollers  502 . That is, the switching flapper  551  is provided with a one-way mechanism that limits the sheet conveying direction. This mechanism causes a sheet on the finisher path  552  in only a direction from right to left as viewed in  FIG. 5  and on the second bookbinding path  554  only in a direction from top to bottom as viewed in  FIG. 5 . 
   Reference numeral  817  denotes a bookbinding inlet sensor that detects the passage of a sheet guided into the first bookbinding path  553 . Reference numeral  813  denotes a pair of bookbinding rollers that convey a sheet having passed through the bookbinding inlet sensor  817 . Reference numeral  820  denotes a housing guide that houses conveyed sheets. Reference numeral  823  denotes a movable sheet positioning member onto which the leading end of a sheet comes into contact so that the sheet is positioned. Reference numeral  818  denotes two pairs of staplers. Reference numeral  819  denotes an anvil provided in opposed relation to the staplers  818  with the housing guide  820  interposed therebetween. The staplers  818  cooperate with the anvil  819  to staple a bundle of sheets at the center thereof. 
   Reference numeral  826  denotes a pair of folding rollers provided below the staplers  818  as viewed in  FIG. 5 . Reference numeral  825  denotes a projecting member provided in opposed relation to the folding rollers  826  with the housing guide  820  interposed therebetween. The projecting member  825  projects toward a bundle of sheets housed in the housing guide  820  to push out the bundle of sheets into a space between the folding rollers  826 . The folding rollers  826  carry out folding processing in which the pushed-out sheets are folded. In carrying out the folding process on a bundle of sheets stapled by the staplers  818 , the stapled position of the sheet bundle is caused to mach the central position (nip point) of the folding rollers  816 . To this end, the sheet positioning member  823  is caused to move down a predetermined distance from the position at which it lies during stapling. Thereafter, the sheet bundle is folded with the stapled position at the nucleus. 
   Reference numeral  827  denotes a pair of sheet discharge rollers that guide a folded sheet bundle. Reference numeral  830  denotes a book-bound discharged sheet sensor that detects the passage of a sheet bundle guided by the sheet output rollers  827 . Reference numeral  813  denotes a discharge tray onto which a sheet bundle having passed through the book-bound discharged sheet sensor  830  is discharged. 
   The inserter  900  feeds sheets stacked on an insert tray  901  to any of the sample tray  701 , stack tray  700 , and output tray  832  via the finisher path  522  or the bookbinding path  553  without passing the sheets through the printer section  300 . 
   It should be noted that in the present embodiment, the user stacks cover sheets or interleaved sheets in the face-up state on the insert tray  901 , described later. 
   Reference numeral  901  denotes the insert tray on which a sheet bundle is stacked. Reference numeral  904  denotes a separation belt that sequentially separates sheets one by one from the top one from the stacked sheet bundle. Reference numeral  903  denotes a separation roller that conveys separated sheets and constitutes a separating section together with the separation belt  904 . Reference numeral  905  denotes a pair of pull-out rollers provided in the vicinity of the separating section;  908 , a conveying path that guides a sheet conveyed from the pullout rollers; and  906 , a pair of conveying rollers that convey a sheet guided on the conveying path  908  to the inlet rollers  502 . Reference numeral  955  denotes an inversion path branched from the conveying path  908 , and reference numeral  956  denotes a path that branches from the inverted path  955  toward the conveying path  908  and is connected to the conveying path  908 . Reference numeral  954  denotes a flapper that selectively switches the destination of a sheet to the conveying path  908 , inversion path  955 , and path  956 . In the case where a sheet on the insert tray  901  is fed in an inverted state, the sheet is from the pull-out rollers  905  to the inversion path  955  so as to be inverted. 
   Reference numeral  952  denotes a pair of inversion rollers that are rotatable forward and backward and convey a sheet conveyed via the inversion path  955 . Reference numeral  951  denotes a tray onto which a sheet conveyed by the inversion rollers  952  is temporarily discharged. When the conveying direction of the inversion rollers  952  is reversed, a sheet is conveyed to the conveying path  908 . 
   Reference numeral  910  denotes a sheet set sensor provided between a sheet feed roller  902  and the separation roller  903 , for detecting whether or not a sheet has been set. Reference numeral  907  denotes a sheet feed sensor provided in the vicinity of the drawing rollers  905 , for detecting whether or not a sheet has been conveyed by the drawing rollers  905 . Reference numeral  953  denotes a set sensor provided between the sheet feed sensor  907  and the inversion rollers  952 , for detecting whether or not a sheet has passed so as to determine whether or not the sheet has been guided into the inversion path  955 . Reference numerals  930  and  931  denote skew sensors provided at different locations downstream of the sheet feed sensor  907  and on the same line orthogonal to the sheet conveying direction. The skew sensors  930  and  931  are used to detect the skewed amount (tilted amount) of a sheet fed from the insert tray  901  of the inserter  900 . 
   In the vicinity of and at a location upstream of the inlet rollers  502 , the conveying path  908  joins the conveying path  402  that guides a sheet from the printer section  300 . 
   Referring next to  FIG. 6 , a description will be given of the construction of the finisher controller  501  that drivingly controls the finisher  500 . 
     FIG. 6  is a block diagram schematically showing the construction of the finisher controller  501  appearing in  FIG. 3 . 
   In  FIG. 6 , reference numeral  560  denotes a CPU circuit section that is comprised of a CPU  562 , a ROM  563  storing various programs, and a RAM  565 . Reference numeral  561  denotes a driver connected to the CPU circuit section  560 , and reference numeral  564  denotes communication IC connected to the CPU circuit section  150  and the CPU circuit section  560  in the copying apparatus  1000 . 
   The CPU circuit section  560  carries out communication with the CPU circuit section  150  of the copying apparatus  1000  via the communication IC  564 . Also, the CPU circuit section  560  drivingly controls the finisher  500  by executing various programs stored in the ROM  563  in accordance with instructions from the CPU circuit section  150 . 
   When the CPU circuit section  560  drivingly controls the finisher  500 , detection signals sent from various sensors are input to the CPU circuit section  560 . 
   The above-mentioned sensors include the inlet sensor  531 , the bookbinding inlet sensor  817 , the book-bound discharged sheet sensor  830 , the sheet feed sensor  907 , the sheet set sensor  910 , the discharged sheet sensor  533 , the skew sensor  930  and  931 , and the set sensor  953  ( FIG. 5 ). 
   The driver  561  drives various motors, solenoids, a clutch CL 1 , a clutch CL 10 , a clutch CL 20 , and so forth in accordance with signals from the CPU circuit section  560 . 
   The above-mentioned motors include an inlet motor M 1 , a buffer motor M 2 , a sheet discharge motor M 3 , a bundle discharge motor M 4 , a conveying motor M 10 , a positioning motor M 11 , a folding motor M 12 , a sheet feed motor M 20 , and a punch motor M 30 . 
   The inlet motor M 1  drives the inlet rollers  502 , the conveying rollers  503 , and the conveying rollers  906 . The buffer motor M 2  drives the buffer roller  505 . The sheet discharge motor M 3  drives the conveying rollers  506 , the discharge rollers  507 , and the discharge rollers  509 . The bundle discharge motor M 4  drives the discharge rollers  680   a  and  680   b . The conveying motor M 10  drives the bookbinding rollers  813 . The positioning motor M 11  drives the sheet positioning member  823 . The folding motor M 12  drives the projecting member  825 , the folding rollers  816 , and the sheet discharge rollers  827 . The sheet discharge motor M 20  drives the sheet feed roller  902 , the separation roller  903 , the separation belt  904 , drawing rollers  905 , and the inversion rollers  952 , which are provided in the inserter  900 . The punch motor M 30  drives the punch roller within the punch unit  550 . 
   The direction in which the inversion rollers  952  are driven by the sheet feed motor M 20  is changed by the clutch CL 20  so that the inversion rollers  952  rotate forward when conveying a sheet in an advancing state and rotated backward when conveying a sheet in an inverted state. 
   The inlet motor M 1 , the buffer motor M 2 , and the sheet discharge motor M 3  are each implemented by a stepping motor. By controlling the excitation pulse rate of current input to each motor, the rollers driven by the motor can be rotated with a uniform speed or different speeds. 
   The inlet motor M 1  and the buffer motor M 2  are caused to freely rotate forward and backward by the driver  561 . 
   The conveying motor M 10 , the positioning motor M 11 , and the sheet feed motor M 20  are each implemented by a stepping motor, and the folding motor M 12  is implemented by a DC motor. 
   The conveying motor M 10  and the sheet feed motor M 20  are configured to convey a sheet in synchronization with the inlet motor M 1 . 
   The above-mentioned solenoids include a solenoid SL 1 , SL 2 , SL 10 , SL 20 , SL 21 , and SL 30 . The solenoid SL 1  selectively changes the position of the switching flapper  510 . The solenoid SL 2  selectively changes the position of the switching flapper  511 . The solenoid SL 10  selectively changes the position of the switching flapper  551 . The solenoid SL 20  drives a sheet feed shutter, not shown, of the inserter  900 . The solenoid SL 21  drives the sheet feed roller  902  of the inserter  900  to move up and down. The solenoid SL 30  drives the flapper  954  of the inserter  900 . 
   A description will now be given of how an operation mode is set. 
     FIG. 7A  is a view showing an example of a postprocessing selection menu screen displayed on a display panel of the operating section  1  of the copying apparatus appearing in  FIG. 1 , and  FIG. 7B  is a view showing an example of a cover designation menu screen displayed on the display panel of the operating section  1 . 
   The display panel in  FIGS. 7A and 7B  has a touch-sensitive panel on a surface thereof. When an operator touches a box in which a function name is displayed on the screen displayed on the display panel, processing corresponding to the touched function name is carried out. 
   In  FIG. 7A , the display panel displays the postprocessing selection menu screen. By way of this screen, the user can select any of a non-sort mode, a sort mode, a staple sort mode (binding mode), a punch mode (hole-punching mode), a bookbinding mode, and so forth, which are operation modes of postprocessing. 
   In  FIG. 7B , the display panel displays the cover sheet designation menu screen. By way of this screen, the user can determine whether a sheet to be inserted is to be fed from the inserter  900  or fed manually. Further, the user can select any of a front cover mode, an interleaving sheet mode, and a back cover mode, which are sheet insertion modes, not shown. The user can select either of the insert tray  901  and the manual sheet feed section  125  as a first stacking section with respect to each insertion mode. It should be noted that the front cover mode is a mode in which a sheet placed on the inserter  900  or the manual sheet feed section  125  is inserted to the first page of sheets conveyed from the printer section  300 . The interleaving sheet mode is a mode in which sheets stacked on the inserter  900  or the manual sheet feed section  125  are inserted as dividers for use as interleaved sheets. The back cover mode is a mode in which a sheet placed on the inserter  900  or the manual sheet feed section  125  is inserted to the last page of sheets conveyed from the printer section  300 . 
   Referring next to  FIGS. 8 and 12 , a description will be given of the flow of a sheet when it is housed on the processing tray  630  in the case where the bookbinding mode is not set. 
     FIG. 8A  is a view showing a direction in which sheets stacked on the insert tray  901  appearing in  FIG. 5  are conveyed, and  FIG. 8B  is a view showing a state in which sheets are stacked on the insert tray  901  of the inserter  900 . 
   In the present embodiment, it is assumed that a sheet (sheet for use as a front cover) conveyed from the inserter  900  and two sheets conveyed from the printer section  300 , i.e. a total of three sheets are housed as one set on the processing tray  630 . 
   In  FIG. 8B , a semicircular mark is written on the front side of a sheet so as to differentiate between the front and back sides of the sheet, and a sheet number or image number is written in the mark. 
   In the case where a sheet of a sheet bundle C on the insert tray  901  is inserted as a cover sheet, the user stacks the sheet bundle in the face-up state and in an erected image on the insert tray  901  as shown on the left side of  FIG. 8A  ( FIG. 8B ). First, a start key, not shown, provided on the operating section  1  is depressed. In response to the depression of the start key, the uppermost sheet of the sheet bundle C (hereinafter referred to as “the sheet C 1 ”) is separated from the sheet bundle C and conveyed to the conveying path  908  ( FIG. 9 ). At this time, since the switching flapper  551  has switched the path to the finisher path  552 , the sheet C 1  is conveyed in the face-down state toward the buffer roller  505  by the inlet rollers  502 . 
   On the other hand, the printer section  300  converts an image read using the moving original reading method into a normal image by carrying out the mirroring process, forms the resulting image on a sheet, and discharges the sheet in the face-down state toward the finisher  500 . 
   The sheet P 1  thus discharged from the printer section  300  is conveyed into the finisher  500  after the leading end of the sheet C 1  conveyed by the inlet rollers  502  passes the inlet sensor  531 , i.e. after the inlet sensor  531  is turned on ( FIG. 10 ). 
   Both of the switching flapper  510  and  511  switch the path to the sort path  522 . The sheet C 1  conveyed to the buffer roller  505  is conveyed to the sort path  522 , and following the sheet C 1 , the sheet P 1  conveyed from the printer section  300  is conveyed in the face-down state into the finisher  500 . 
   The sheet C 1  conveyed to the sort path  522  is conveyed to the processing tray  630  ( FIG. 11 ) The sheet P 1  conveyed from the printer section  300  into the finisher  500  following the sheet C 1  is conveyed to the sort path  522  via the finisher path  552  and the buffer roller  505 . 
   At this time, conveyance of a sheet P 2  from the printer section  300  to the finisher  500  is started following the conveyance of the sheet P 1 . 
   In outputting the second set, a sheet which follows the uppermost sheet C 1  of the sheet bundle C stacked on the insert tray  901  (hereinafter referred to as “the sheet C 2 ”) is separated from the sheet bundle C by the separating section of the inserter  900  so as to be used as a front cover of the second set. 
   Next, the sheet C 1  is housed in on the processing tray  630  in such a manner that the sheet C 1  lies in the face-down state with the binding position thereof on the stapler  601  side. The sheet P 2  following the sheet C 1  is conveyed to the processing tray  630  as is the case with the sheet C 1  and housed on the processing tray  630  where it is laid over the sheet C 1 . 
   In outputting the second set, the sheet C 2  following the sheet P 2  is conveyed to the conveying path  908 . While the sheet P 2  is being conveyed toward the processing tray  630 , however, the conveyance of the sheet C 2  is temporarily stopped so that the sheet C 2  is at a standstill in front of the conveying rollers  906 . In synchronization with timing in which the sheet P 2  is housed on the processing tray  630 , the conveyance of the sheet C 2  is resumed. 
     FIG. 12A  is a view showing a sheet bundle stacked on the processing tray  630  appearing in  FIG. 5 ,  FIG. 12B  is a view showing a sheet bundle of which front cover is the sheet C 1 , and  FIG. 12C  is a view showing a sheet bundle of which back cover is the sheet C 2 . 
   In  FIG. 12A , normal images converted from images output from the image reader section  200  by carrying out the mirroring process are formed on the sheets P 1  and P 2  stacked on the processing tray  630 . 
   Also, the finisher  500  inverts sheets stacked in the inserter  900  and sheets conveyed from the printer section  300  in the face-down state to the processing tray  630 . It should be noted that the conveyance of the sheets stacked in the inserter  900  is carried out prior to the conveyance of the sheets from the printer section  300 . 
   The sheets P 1  and P 2  housed on the processing tray  630  lie in the face-down state with the binding positions thereof on the stapler  601  side as is the case with the sheet C 1 . 
   In the case where the stapling process is carried out as postprocessing on the sheet bundle housed on the processing tray  630 , the stapling process is carried out by the stapler  601  immediately after the sheet P 2  is housed on the processing tray  630 . The sheets of the sheet bundle on which the stapling process has been carried out are identical in image orientation and binding position and book-bound as shown in  FIG. 12B . 
   In this way, the finisher  500  can carry out first-page processing, in which sheets conveyed from the inserter  900  and sheets conveyed from the printer section  300  are collated when they are mixed, and postprocessing in a compatible manner. Also, in the case where postprocessing is carried out on the mixed sheet bundle, the alignment of the sheets can be facilitated, which prevents the occurrence of troubles. 
   If the orientation of originals (front, back, top and tail) stacked on the tray  1001  and the orientation of sheets (front, back, top and tail) stacked on the insert tray  901  are made identical, formed images and inserted sheets can be identical in orientation. Thus, originals may be stacked in the erected image and in the face-up state so that the user can easily stack them, and therefore it is possible to prevent the orientations of inserted sheets and formed images from becoming inappropriate and to improve the ease of operation. 
   Further, since the original feeder  100  and the inserter  900  are constructed such that the direction in which originals stacked on the tray  1001  are fed (from right to left as viewed in  FIG. 1 ) and the direction in which sheets stacked on the insert tray  901  are fed (from left to right as viewed in  FIG. 1 ) are opposite to each other, and the tray  1001  and the insert tray  901  face externally from the copying system  2000 , the copying system  2000  can be made compact. Also, the ease of stacking in the inserter  900  can be improved. 
   Although in the present embodiment, the printer section  300  forms output images on sheets, the present invention is not limited to this, but images input from the external computer  210  may be formed on sheets. In this case as well, rotation processing such as mirroring is carried out on images input from the external computer  210  as necessary in consideration of image orientations and binding positions of sheets stacked on the insert tray  901 . Then, the images on which such processing has been carried out are formed on the sheets, and the sheets with the images formed thereon are inverted and discharged to the finisher  500 . 
   In the description of the present embodiment, it is assumed that the front cover mode in which a sheet placed on the insert tray  901  is inserted to the first page of sheets conveyed from the printer section  300  is set. The same process is carried out in the case where the interleaving sheet mode in which sheets stacked on the insert tray  901  are inserted as dividers for use as interleaved sheets to middle pages of sheets conveyed from the printer section  300  is set and the case where the back cover mode in which a sheet placed on the insert tray  901  is inserted to the last page of sheets conveyed from the printer section  300  is set. In the case where the back cover mode is set, not the sheets C 1 , P 1 , and P 2  but the sheets P 1 , P 2 , and C 2  are discharged to the processing tray  630 . In this way, a sheet placed on the inset tray  901  or the manual sheet feed section  125  can be inserted to the last page of sheets conveyed from the printer section  300 . On this occasion, the sheet C 2  is conveyed to the finisher path  552  after being inverted by an inverted sheet feed process, described later, and thereafter, the same processing as in the front cover mode is carried out on the sheet C 2 . In the case where the stapling process is carried out, the sheets are bound as shown in  FIG. 12C . 
   Although in the present embodiment, sheets stacked on the insert tray  901  are inserted into a sheet bundle conveyed from the printer section  300 , sheets stacked not only on the insert tray  901  but on the manual sheet feed section  125  may be inserted into a sheet bundle conveyed from the printer section  300 . In this case, the same processing is carried out. 
   Referring now to  FIGS. 13 to 22 , a description will be given of the flows of sheets conveyed from the inserter  900  and the printer section  300  when the finisher houses them on the housing guide  820 . 
   The bookbinding mode is a mode in which the finisher  500  inserts a sheet placed on the insert tray  901  which is for use as a front cover into a sheet bundle discharged from the printer section  300  and binds a book by carrying out the folding process and the binding process on the sheet bundle into which the front cover has been inserted. 
     FIG. 13  is a view useful in explaining an image forming process carried out by the printer section  300  in the case where the bookbinding mode is set as the operation mode. 
   The bookbinding mode is set as the operation mode through operation of the operating section  1 , and the start key is depressed. In response to the depression of the start key, the image reader section  200  reads a plurality of originals stacked on the tray  1001  of the original feeder  100  sequentially from the first page, and the read original images are sequentially stored in the hard disk  206  within the image signal controller  202 . On this occasion, the image reader section  200  counts the number of the originals which have been read. When reading of all the originals is completed, the order in which the plurality of read original images are formed on sheets and the positions on the sheets at which the images are formed are determined using the following expression (1):
 
 M=n× 4− k   (1)
 
   In the expression (1), M is the number of originals, n is the number of sheets on which read original images are to be formed (n is an integer of 1 or more), and k is any of values 0, 1, 2, and 3. 
   Assuming that the number of read originals is eight, a description will now be given of the image forming process carried out in the bookbinding mode. 
   In the hard disk  206 , original image data of eight pages (R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 ) are stored in an order in which they are read ( FIG. 13A ). In accordance with the image formation sequence and the positions on the sheets at which the images are formed, which have been determined based on the above expression (1), the printer section  300  forms the image R 4  on a left half of a first surface (front side) of a first-page sheet P 1  and forms the image R 5  on a right half of the first surface ( FIG. 13B ). The images formed on the sheet are images obtained by carrying out the above described mirroring process. 
   The printer section  300  conveys the sheet P 1  with the images R 4  and R 5  formed thereon to the transfer section  116  again via the double-sided conveying path  124  to form the image R 5  on a left half of a second surface (back side) of the sheet P 1  and form the image R 3  on a right half of the second surface. 
   The sheet P 1  with the images formed on both sides thereof by the above described process is discharged from the printer section  300  without being inverted, i.e. with the back side thereof facing upward and conveyed to the first bookbinding path  553  of the finisher  500 . 
   In conveying the sheet P 1  to the finisher  500 , the printer section  300  conveys the sheet P 1  in a direction indicated by an arrow in  FIG. 13C  in a state in which the second surface on which the images R 6  and R 3  are formed are facing upward and the image R 6  lies at the leading end ( FIG. 13C ). 
   In this case, the image R 5  is formed on the back side of a part where the image R 6  is formed, and the image R 4  is formed on the back side of a part where the image R 3  is formed. 
   Subsequently to the above described process, the printer section  300  forms the image R 2  on a left half of a first surface (front side) of a second-page sheet P 2  and forms the image R 7  on a right half of the first surface ( FIG. 13B ). The images formed on the sheet are images obtained by carrying out the above described mirroring process. 
   The printer section  300  conveys the sheet P 2  with the images R 2  and R 7  formed thereon to the transfer section  116  again via the double-sided conveying path  124  to form the image R 8  on a left half of a second surface (back side) of the sheet P 2  and form the image R 1  on a right half of the second surface. 
   The sheet P 2  with the images formed on both sides thereof by the above described process is discharged from the printer section  300  without being inverted, i.e. with the second surface thereof facing upward and conveyed to the first bookbinding path  553  of the finisher  500 . 
   In conveying the sheet P 2  to the finisher  500 , the printer section  300  conveys the sheet P 2  in a direction indicated by an arrow in  FIG. 13C  in a state in which the second surface on which the images R 8  and R 1  are formed are facing upward and the image R 8  lies at the leading end ( FIG. 13C ). 
   In this case, the image R 7  is formed on the back side of a part where the image R 8  is formed, and the image R 2  is formed on the back side of a part where the image R 1  is formed. 
   After being subjected to the above described process, the sheets P 1  and P 2  are sequentially conveyed into and housed in the housing guide  802  via the first bookbinding path  553  of the finisher  500 . In the housing guide  820 , the sheets P 1  and P 2  are housed on the projecting member  715  side and the folding roller pair  816  side with their respective first surfaces facing to the projecting member  825  ( FIG. 13D ). After that, the sheet positioning member  823  positions the sheets P 1  and P 2  in the housing guide  820 . 
     FIGS. 14A and 14B  are views useful in explaining a bookbinding process carried out by the finisher  900  appearing in  FIG. 1  in the case where the bookbinding mode is set as the operation mode. 
   The user stacks a sheet bundle including a sheet C 1  on the insert tray  901 . On this occasion, the sheet C 1  is placed on the insert tray  901  with a surface thereof on which an image R and an image F are formed facing upward, i.e. in an erected image as viewed from the user and in the face-up state ( FIGS. 15A and 15B ). Since the orientation of the sheet C 1  placed on the insert tray  901  is the same as the orientation of originals stacked on the original feeder  100 , the ease of operation in placing the sheet C 1  on the insert tray  901  can be improved. 
   When the start key of the operating section  1  is depressed with the bookbinding mode set as the operation mode, a sheet P 1  conveyed from the printer section  300  is conveyed to the finisher  500  ( FIG. 18A ). The sheet P 1  is conveyed to the first bookbinding path  553  by operation of the switching flapper  551  and housed in the housing guide  820 , and following the sheet P 1 , a sheet P 2  is conveyed to the first bookbinding path  553  ( FIG. 18B ). 
   At this time, the flapper  954  has switched the path to the inversion path  955 , and hence the sheet C 1  is inverted through the inversion path  955  ( FIG. 16A ). The sheet C 1  is then conveyed to the path  908  ( FIG. 16B ), conveyed to the first bookbinding path  553  ( FIG. 17A ), and housed in the housing guide  820 . At this time, since the sheet C 1  has been inverted once, the sheet C 1  is conveyed to the housing guide  820  with the surface on which the image R is formed being at the leading end, and laid over the sheet bundle comprised of the sheets P 1  and P 2  that have been already housed in the housing guide  820  ( FIGS. 13D and 17B ). 
   In outputting a second set, when the sheet C 1  is housed in the housing guide  820 , a sheet C 2  for use as a front cover is separated from the sheet bundle by the separating section of the inserter  900 , inverted as is the case with the sheet C 1 , and conveyed to a position in front of the conveying rollers  906 . The conveyance of the sheet C 2  is temporarily stopped and retained at a position in front of the conveying rollers  906  until all the sheets P 1 , P 2 , C 1 , P 3 , P 4  are housed in the housing guide  820  ( FIG. 17B ). The conveyance of the sheet C 2  is resumed in synchronization with timing in which all the sheets P 1 , P 2 , C 1 , P 3 , and P 4  are housed in the housing guide  820 . 
   If it is determined in a step S 2010  in  FIG. 21 , described later, that the sheet C 2  is an inappropriate sheet, e.g. a sheet having a different size from a predetermined size, the sheet C 2  is discharged onto the sample tray  701  via the buffer roller  505  without being stopped ( FIG. 19 ). 
   After the sheet C 1  is housed in the housing guide  820 , the finisher  500  causes the projecting member  825  to project toward the sheet bundle comprised of the sheets C 1 , P 1 , and P 2 , so that the sheet bundle is pushed out to a position between the folding rollers  826  ( FIG. 14A ). As a result, the sheet bundle is folded into two leaves and discharged onto the discharge tray  832 . 
   In the folded sheet bundle, the image F on the sheet C 1  is disposed on the front cover page, and the image R on the sheet C 1  is disposed on the last page ( FIG. 14B ). Since the images on the sheets P 1  and P 2  are arranged according to page order, the images on the sheets C 1 , P 1 , and P 2  can be identical in orientation. 
   As described above, the finisher  500  can bind a book in which images are arranged in the same orientation by arranging the images on the sheet C 1  conveyed from the inserter  900  on the first page and the last page and arrange the images on the sheets P 1  and P 2  conveyed from the printer section  300  according to page order. 
   It should be noted that, with the C 1  housed in the housing guide  820 , the stapler  818  may staple the sheet bundle at the midsection thereof. In this case, the sheet bundle is bound at the left end thereof as shown in  FIG. 14B . 
   A description will now be given of processes associated with control of conveyance in the finisher  500 . 
     FIG. 20  is a flow chart showing the procedure of an operation mode determining process carried out by the finisher controller  501  appearing in  FIG. 6 . 
   The process in  FIG. 20  is carried out by the CPU circuit section  560  of the finisher controller  501  in accordance with instructions from the CPU circuit section  150 . 
   As shown in  FIG. 20 , the CPU circuit section  560  determines whether or not a finisher start signal which instructs initiation of the finisher  500  has been input from the CPU circuit section  150  to the finisher controller  501  (step S 1901 ). The finisher start signal is input from the CPU circuit section  150  to the finisher controller  501  when the start key of the operating section  1  is depressed by the user to instruct the copying apparatus  1000  to start copying. 
   If, as a result of the determination in the step S 1901 , the finisher start signal has not been input to the finisher controller  501 , the above determination is repeatedly carried out until the finisher start signal is input to the finisher controller  501 . When the finisher start signal is input to the finisher controller  501 , the CPU circuit section  560  starts driving the inlet motor M 1  (step S 1902 ). The CPU circuit section  560  determines whether or not there is a sheet feed request for the inserter  900  based on data sent from the communication IC  564  (step S 1903 ). The sheet feed request is input to the finisher controller  501  when the user selects “Inserter” on the front cover designation menu screen ( FIG. 7B ) displayed on the display panel of the operating section  1 . 
   If, as a result of the determination in the step S 1903 , there is the sheet feed request for the inserter  900 , an inserter sheet pre-feed process in  FIG. 21 , described later, is carried out (step S 1904 ). If there is no sheet feed request for the inserter  900 , the CPU circuit section  560  goes to a step S 1905  without carrying out the process in the step S 1904 . 
   In the next step S 1905 , the CPU circuit section  560  causes the CPU circuit section  150  to start an image forming process by outputting a sheet feed signal which gives a sheet feed permission to the CPU circuit section of the copying apparatus  1000  via the communication IC  564  (step S 1905 ). The CPU circuit section  560  determines whether or not the bookbinding mode has been set as the set operation mode based on processing mode data received from the CPU circuit section  150  via the communication IC  564  (step S 1906 ). 
   If, as a result of the determination in the step S 1906 , the bookbinding mode has been set as the operation mode, the CPU circuit section  560  carries out a bookbinding process in  FIG. 22 , described later (step S 1907 ). Upon completing the process in the step S 1907 , the CPU circuit section  560  returns to the step S 1901 . 
   If, as a result of the determination in the step S 1906 , the bookbinding mode has not been set as the operation mode, the CPU circuit section  560  determines whether or not the operation mode set by the user via the postprocessing selection menu screen ( FIG. 7A ) is the punch mode (step S 1913 ). If the punch mode has been set as the operation mode, the CPU circuit section  560  turns on a punch mode flag (step S 1914 ) and goes to a step S 1908 . If the punch mode has not been set as the operation mode, the CPU circuit section  560  goes to the step S 1908  without carrying out the process in the step S 1914 . 
   In the next step S 1908 , the CPU circuit section  560  determines whether or not the set operation mode is the non-sort mode, the sort-mode, or the staple sort mode. If the set operation node is the non-sort mode, the CPU circuit section  560  carries out a non-sort process (step S 1909 ) and then goes to a step S 1912 , described later. If the set operation node is the sort mode, the CPU circuit section  560  carries out a sort process (step S 1910 ) and then goes to the step S 1912 , described later. If the set operation node is the staple sort mode, the CPU circuit section  560  carries out a staple sort process (step S 1911 ) and then goes the step S 1912 , described later. 
   In the next step S 1912 , the CPU circuit section  560  stops driving the inlet motor M 1 . The CPU circuit section  560  then returns to the step S 1901  to wait for the input of the finisher start signal, but if the punch mode flag was turned on in the step S 1914 , the CPU circuit section  560  turns off the punch mode flag and returns to the step S 1901 . 
   It should be noted that in carrying out processing in any of the steps S 1907 , S 1909 , S 1910 , and S 1911 , the CPU circuit section  560  carries out the inserter sheet pre-feed process in the step S 1904  first if determining in the step S 1903  that there is the sheet feed request for the inserter  900 . 
     FIG. 21  is a flow chart showing the procedure of the inserter sheet pre-feed process in the step S 1904  in  FIG. 20 . 
   The process in  FIG. 21  is carried out if, as a result of the determination in the step S 1903  in FIG.  20 , there is the sheet feed request for the inserter  900 . Specifically, the process conveys a sheet from the inserter  900  to the finisher  500  prior to conveyance of a sheet from the printer section  300  to the finisher  500  and is carried out by the CPU circuit section  560  of the finisher controller  501 . 
   In  FIG. 21 , the CPU circuit section  560  carries out sheet pre-feed checking to determine whether or not sheet feed conditions for feeding a sheet from the inserter  900  has been satisfied (step S 2001 ). Specifically, the CPU circuit section  560  determines whether or not there is a sheet on the insert tray  901  and checks information related to designated size data input via the operating section  1  and sends an image formation inhibition signal to the CPU circuit section  150  of the copying apparatus  1000 . 
   Next, in a step S 2002 , the CPU circuit section  560  drives the shutter solenoid SL 20  to move down the sheet feed roller  902  and open a sheet feed shutter, not shown, of the inserter  900 . Further, the CPU circuit section  560  drives the pickup solenoid SL 21  to cause the sheet feed roller  902  to land on the sheet on the insert tray  901  and turns on the clutch CL  10  to transmit driving force of the sheet feed motor M 20  to the sheet feed roller  902  (pre-separation process). 
   Next, in a step S 2003 , the CPU circuit section  560  starts driving the sheet feed motor M 20  upon the lapse of a predetermined time period. Further, by rotating the separation roller  903 , the separation belt  904 , and the pull-out rollers  905  of the inserter  900 , the CPU circuit section  560  separates a sheet C 1  which is the uppermost sheet of a sheet bundle C and conveys the sheet C 1  to the conveying path  908  (separation process). 
   Next, in a step S 2004 , the CPU circuit section  560  determines whether or not predetermined settings have been made through the operating section  1 . If the predetermined settings have been made, the CPU circuit section  560  carries out a sheet inverting process out (step S 2005 ) and then goes to a step S 2006 , described later (first sheet feed mode). If the predetermined settings have not been made, the CPU circuit section  560  goes to the step S 2006 , described later, without carrying out the process in the step S 2005  (second sheet feed mode). The predetermined settings include a setting to designate the sheet C 1  as a back cover of sheets discharged in an inverted state from the printer  300  and a setting to carry out the bookbinding process. 
   Next, in the step S 2006 , the CPU circuit section  560  carries out a skew detecting process in  FIG. 24 , describe later, and in a step S 2007 , the CPU circuit section  560  carries out a first conveying process. 
   In the first conveying process in the step S 2007 , the CPU circuit section  560  monitors the status of the conveyance of the sheet C 1  using the sheet feed sensor  907 . When the sheet feed sensor  907  detects the leading end of the sheet C 1 , the CPU circuit section  560  turns off the clutch CL 10  and starts counting clocks output from a clock sensor provided in the sheet feed motor M 20 . The CPU circuit section  560  drives the sheet feed motor M 20  until the counted value becomes equal to a predetermined value N 1 . The counting is carried out until each of the sheet feed sensor  907  and the set sensor  953  stops detecting the sheet C 1 . The first conveying process is intended to convey a sheet conveyed from the inserter  900  via the pull-out rollers  905  to a position in front of the conveying rollers  906  and temporarily stops the sheet at this position ( FIG. 17B ). 
   Next, in a step S 2008 , the CPU circuit section  560  determines whether or not a request for re-feeding the sheet C 1  has been given to the inserter  900  from the CPU circuit section  150  of the copying apparatus  1000  and repeatedly carries out this determination until a request for re-feeding the sheet C 1  is given from the CPU circuit section  150  of the copying apparatus  1000  to the CPU circuit section  560  of the finisher controller  501 . In response to the request for re-feeding the sheet C 1 , a second conveying process is carried out (step S 2009 ). 
   In the second conveying process in the step S 2009 , the CPU circuit section  560  resumes driving the sheet feed motor M 20  to convey the sheet C 1  being at a standstill in front of the conveying rollers  906  toward the inlet rollers  502 . After that, when the sheet feed sensor  907  or the set sensor  953  detects the trailing end of the sheet C 1 , the CPU circuit section  560  terminates the counting operation started in the processing in the step S 2003 . The CPU circuit section  560  calculates the length of the sheet C 1  in the conveying direction thereof based on the value counted by the counting operation. 
   Next, in a step S 2010 , the CPU circuit section  560  determines whether or not the sheet C 1  has an appropriate size based on the calculated length of the sheet C 1  in the conveying direction thereof and the designated size data acquired in the processing in the step S 2001 . If the sheet C 1  has an appropriate size, the CPU circuit section  560  causes the switching flapper  510  to switch the path to the non-sort path  521 . Further, the CPU circuit section  560  drives the buffer motor M 2  and the sheet discharge motor M 3  to discharge the sheet C 1  onto the sample tray  701  via the non-sort path  521 . Further, the CPU circuit section  560  notifies the CPU circuit section  150  of the copying apparatus  1000  that the sheet C 1  with an inappropriate size has been conveyed from the inserter  900  (step S 2011 ), carries out an inserter stopping process (step S 2012 ), and terminates the present process. 
   In the inserter stopping process in the step S 2012 , the CPU circuit section  560  cancels the image formation inhibition signal sent from the CPU circuit section  560  to the CPU circuit section  150  in the step S 2001  and stops driving the sheet feed motor M 20 . Also, the CPU circuit section  560  detects whether or not there is a sheet on the insert tray  901  using the sheet set sensor  910  and continues driving the shutter solenoid SL 20  while the sheet lies on the insert tray  901 . 
   If, as a result of the determination in the step S 2010 , the sheet C 1  has an appropriate size, the CPU circuit section  560  determines the operation mode set through the operating section  1  (step S 2013 ). 
   If, as a result of the determination in the step S 2013 , the operation mode is the non-sort mode, the CPU circuit section  560  carries out a non-sort sheet pre-feed process in which the sheet C 1  conveyed from the inserter  900  is discharged onto the sample tray  701  (step S 2014 ). After that, the CPU circuit section  560  carries out the process in the step S 2012  and terminates the present process. 
   If, as a result of the determination in the step S 2013 , the operation mode is the sort mode or the staple sort mode, the CPU circuit section  560  carries out a pre-stacking sheet feed process in which the switching flappers  510  and  511  are caused to switch the path to the sort path  533  so that the sheet C 1  is guided to the processing tray  630  (step S 2015 ). After that, the CPU circuit section  560  carries out the process in the step S 2012  and terminates the present process. 
   In the pre-stacking sheet feed process in the step S 2015 , when the sheet C 1  conveyed from the inserter  900  is set to be used as a front cover, the sheet C 1  conveyed from the inserter  900  is placed in the face-down state on the processing tray  630  and aligned on the processing tray  630 . When the sheet C 1  are set to be used as a back cover, it is placed in the face-up state and aligned on the processing tray  630 . Also, it becomes possible for the stapler  601  to bind a book by stapling a sheet bundle comprised of a plurality of sheets stacked on the processing tray  630 . 
   If, as a result of the determination in the step S 2013 , the operation mode is the bookbinding mode, the CPU circuit section  560  carries out a bookbinding sheet pre-feed process in which the sheet C 1  is held on standby in the conveying path  908  (step S 2016 ) ( FIG. 17B ), carries out the process in the step S 2012 , and terminates the present process. 
   According to the process in  FIG. 21 , if the sheet C 1  does not have an appropriate size (“NO” to the step S 2010 ), the CPU circuit section  560  causes the switching flapper  510  to switch the path to the non-sort path  521 . Further, the CPU circuit section  560  drives the buffer motor M 2  and the sheet discharge motor M 3  to discharge the sheet C 1  onto the sample tray  701  via the non-sort path  521 . Further, the CPU circuit section  560  notifies the CPU circuit section  150  of the copying apparatus  1000  that the sheet C 1  with an inappropriate size has been conveyed from the inserter  900  (step S 2011 ) and carries out the inserter stopping process (step S 2012 ). By carrying out these processes, it is possible to recognize the size of a front cover in advance when stacking sheets conveyed from the inserter  900  conveyed from the inserter  900  and sheets conveyed from the printer section  300  in a mixed state. Further, the system-down of the copying system  2000  caused by a mismatch between the size of sheets conveyed from the inserter  900  and sheets conveyed from the printer section  300  can be suppressed to the minimum possible level. 
     FIG. 22  is a flow chart showing the procedure of the bookbinding process in the step S 1907  in  FIG. 20 . 
   The process in  FIG. 22  is carried out if, as a result of the determination in the step S 1906  in  FIG. 20 , the operation mode is the bookbinding mode and is carried out by the CPU circuit section  560  of the finisher controller  501 . 
   As shown in  FIG. 22 , the CPU circuit section  560  determines whether or not the size of a sheet conveyed from the printer section  300  to the finisher  500  is a size that can be book-bound based on size information (step S 2101 ). 
   If, as a result of the determination in the step S 2101 , the size of a sheet conveyed from the printer section  300  to the finisher  500  is not a size that can be book-bound, the CPU circuit section  560  immediately terminates the present process, and if the size of a sheet conveyed from the printer section  300  to the finisher  500  is a size that can be book-bound, the CPU circuit section  560  carries out initial operation for bookbinding (step S 2102 ). 
   In the initial operation for bookbinding in the step S 2102 , the CPU circuit section  560  drives the conveying motor  813  to rotate the bookbinding rollers  813 , thereby making sheet conveyance possible. Further, the CPU circuit section  560  drives the switching solenoid SL 10  to cause the switching flapper  551  to switch the path to the first bookbinding path  553 , so that a sheet from the printer section  300  is guided to the housing guide  820 . The CPU circuit section  560  positions a truing-up member, not shown, such that the width thereof has a predetermined amount of margin relative to the sheet width. Further, the CPU circuit section  560  rotates the positioning motor M 11  a predetermined number of steps so that the distance from the sheet positioning member  823  to the stapling position of the stapler  818  can be half the length of a sheet in the conveying direction thereof. 
   Next, in a step S 2103 , based on a signal output from the bookbinding inlet sensor  817 , the CPU circuit section  560  determines whether or not the sheet conveyed from the printer section  300  has been conveyed into the housing guide  820 . If the sheet conveyed from the printer section  300  has not yet been conveyed into the housing guide  820 , the CPU circuit section  560  returns to the step S 2102 . If the sheet conveyed from the printer section  300  has been conveyed into the housing guide  820 , the CPU circuit section  560  activates the truing-up member, not shown, upon the lapse of a predetermined time period to align the sheet housed in the housing guide  820  in the direction of the sheet width (step S 2104 ). 
   Next, in a step S 2105 , the CPU circuit section  560  determines whether or not the sheet processed in the step S 2104  is the last sheet of sheets that should be bound into a book. If the sheet is the last sheet, the CPU circuit section  560  returns to the step S 2102 . If the sheet is the last sheet, the CPU circuit section  560  outputs an image formation prohibition signal to the CPU circuit section  150  so as to inhibit sheet conveyance from the printer section  300  to the finisher  500  (step S 2106 ) and then goes to a step S 2107 . 
   In the next step S 2107 , the CPU circuit section  560  determines whether or not the user has instructed sheet feed from the inserter  900  via the screen view on the display panel of the operating unit ( FIG. 7B ). If the user has instructed sheet feed from the inserter  900 , the CPU circuit section  560  carries out an inserter sheet feed process in  FIG. 23 , described later (step S 2108 ) and carries out the stapling process on the sheet bundle aligned in the housing guide  820  (step S 2109 ). If the user has not instructed sheet feed from the inserter  900 , the CPU circuit section  560  carries out the stapling process without carrying out the inserter sheet feed process in the step S 2108  (step S 2109 ). 
   Next, in a bundle conveying process in a step S 2110 , the CPU circuit section  560  drives the positioning motor M 1  to move down the sheet positioning motor  823  and drives the conveying motor M 10  again to rotate the bookbinding rollers  813 . As a consequence, the sheet bundle is conveyed by an amount corresponding to the distance between the stapling position of the stapler  818  and the nip position of the folding rollers  825 . 
   Next, in a step S 2111 , the CPU circuit section  560  drives the clutch CL 1  and the folding motor M 12  to move the projecting member  825  toward the folding rollers  826  (as indicated by the arrow in  FIG. 14A ). As a consequence, the center of the sheet bundle which is the stapled position on the sheets is guided to the nip point of the folding rollers  826 , and the sheet bundle is folded into two leaves by the projecting member  825  and the folding rollers  826  (folding control process). It should be noted that the projecting member  825  is configured to be caused to reciprocate by a cam mechanism. The CPU circuit section  560  stops driving the clutch CL 1  when a sensor, not shown, detects that the projecting member  825  has made one reciprocating motion. Next, in a step S 2112 , the CPU circuit section  560  determines whether or not the sheet bundle has been discharged onto the discharge tray  832  using the book-bound discharged sheet sensor  830  which detects the trailing end of a sheet folded into two leaves. The CPU circuit section  560  repeatedly carries out the above determination until the sheet bundle is discharged to the discharge tray  832 . When the sheet bundle is discharged onto the discharge tray  832 , the CPU circuit section  560  stops driving the folding motor M 12  (step S 2113 ). Further, the CPU circuit section  560  determines whether or not the sheet bundle is the last sheet bundle to be book-bound (step S 2114 ). If the sheet bundle is the last sheet bundle to be book-bound, the CPU circuit section  560  terminates the bookbinding mode by moving the truing-up member and the sheet positioning member  823  to their respective predetermined waiting positions and switching the switching flapper  551  to enable passage through the finisher path  522  (step S 2115 ) and then terminates the present process. 
   If, as a result of the determination in the step S 2114 , the sheet bundle is the sheet bundle to be book-bound, the CPU circuit section  560  cancels the image formation inhibition signal, notifies the CPU circuit section  150  of the cancellation (step S 2116 ), and then returns to the step S 2102 . 
     FIG. 23  is a flow chart showing the procedure of the inserter sheet feed process in the step S 2108  in  FIG. 22 . 
   The process in  FIG. 23  is carried out if, as a result of the determination in the step S 2107  in  FIG. 22 , sheet feed from the inserter  900  has been instructed. In the process in  FIG. 23 , a sheet is conveyed from the inserter  900  to the housing guide  820 . 
   In the present embodiment, the inserter sheet pre-feed process in  FIG. 21  is carried out prior to the inserter sheet feed process. As a result of the pre-bookbinding sheet feed process in the step S 2016  of the inserter sheet pre-feed process in  FIG. 21 , a sheet C 1  from the inserter  900  waits on the conveying path  908  ( FIG. 16B ). 
   As shown in  FIG. 23 , the CPU circuit section  560  sets the rotational directions of the feed motor M 20  and the inlet motor M 1  to forward directions and drives them. Further, the CPU circuit section  560  drives the conveying motor M 10  to start conveying the sheet C 1  waiting at the conveying path  908  to the first bookbinding path  553  ( FIG. 17A ) (step S 2201 ). The CPU circuit section  560  then determines whether or not the trailing end of the sheet C 1  has been detected by the bookbinding inlet sensor  817  (step S 2202 ). The CPU circuit section  560  repeatedly carries out the above determination until the trailing end of the sheet C 1  is detected by the bookbinding inlet sensor  817 . When the trailing end of the sheet C 1  is detected by the bookbinding inlet sensor  817 , the CPU circuit section  560  stops driving the inlet motor M 1  and the feed motor M 20  (finisher driving stopping process) (step S 2203 ). That is, in the step S 2202 , the CPU circuit section  560  continues to convey the sheet C 1  until the trailing end of the sheet C 1  from the inserter  900  is detected. 
   Next, in a step S 2204 , the CPU circuit section  560  determines whether or not the sheet bundle being currently processed is the last sheet bundle to be book-bound. If the sheet bundle being currently processed is the last sheet bundle to be book-bound, the CPU circuit section  560  goes to a step S 2206 . If the sheet bundle being currently processed is not the last sheet bundle to be book-bound, the CPU circuit section  560  issues a start command for starting the inserter sheet pre-feed process in  FIG. 21  to start the inserter sheet pre-feed process and carries out the inserter sheet pre-feed process in tandem with the bookbinding process in  FIG. 22  (step S 2205 ). 
   Next, in the step S 2206 , the CPU circuit section  560  determines whether or not the sheet C 1  conveyed from the inserter  900  has been conveyed into the housing guide  820  using the bookbinding inlet sensor  817  which detects the trailing end of each sheet. The CPU circuit section  560  repeatedly carries out the above determination until the sheet C 1  conveyed from the inserter  900  is conveyed into the housing guide  820 . When the sheet C 1  conveyed from the inserter  900  is conveyed into the housing guide  820 , the CPU circuit section  560  activates the truing-up member upon the lapse of a predetermined time period and aligns the sheet C 1  housed in the housing guide  820  in the direction of the sheet width (step S 2207 ) and terminates the present process. 
     FIG. 24  is a flow chart showing the procedure of the skew detecting process in the step S 2006  in  FIG. 21 . 
   The process in  FIG. 24  is carried out by the CPU circuit section  560  of the finisher controller  501 . 
   As shown in  FIG. 24 , the CPU circuit section  560  determines whether or not the skew sensor  930  is on (step S 2301 ). If the skew sensor  930  is on, the CPU circuit section  560  determines whether or not the skew sensor  931  is on (step S 2302 ). If the skew sensor  931  is not on, the CPU circuit section  560  returns to the step S 2301 . 
   That is, the CPU circuit section  560  repeatedly carries out the processes in the steps S 2301  and S 2302  until one of the skew sensor  930  and the skew sensor  931  is turned on, i.e. until the leading end of a sheet reaches one of the skew sensor  930  and the skew sensor  931 . 
   As described above, the skew sensors  930  and  931  are located at respective different positions on a line orthogonal to the sheet conveying direction. Thus, when a sheet conveyed from the insert tray  901  skews, the leading end of the conveyed sheet is detected first by one of the skew sensors  930  and  931 . 
   If, as a result of the determination in the step S 2301 , the skew sensor  930  is on, the CPU circuit section  560  assigns 0 to a variable SKEW_CN corresponding to a counter for the detection of skew (step S 2303 ). Further, the CPU circuit section  560  turns on a skew detection flag “skew_detect_flg” (step S 2304 ) and determines whether or not the skew sensor  931  is on (step S 2305 ). The CPU circuit section  560  repeatedly carries out the above determination until the skew sensor  931  is on, and when the skew sensor  931  is on, the CPU circuit section  560  goes to a step S 2309 , described later. 
   If, as a result of the determination in the step S 2302 , the skew sensor  931  is on, the CPU circuit section  560  assigns 0 to the variable SKEW_CN corresponding to the counter for the detection of skew (step S 2306 ). Further, the CPU circuit section  560  turns on the skew detection flag “skew_detect_flg” (step S 2307 ) and determines whether or hot the skew sensor  930  is on (step S 2308 ). The CPU circuit section  560  repeatedly carries out the above determination until the skew sensor  930  is on, and when the skew sensor  930  is on, the CPU circuit section  560  returns to the step S 2309 , described later. 
   Next, in the step S 2309 , the CPU circuit section  560  turns off the flag “skew_detect_flg.” The CPU circuit section  560  then checks the count value SKEW_CN counted from the turning-on of the flag “skew_detect_flg” to the turning-off of the flag “skew_detect_flg” and calculates the skew amount of the sheet relative to the sheet feed direction based on the value of the variable SKEW_CN. 
   Next, in a step S 2310 , the CPU circuit section  560  determines whether or not the value of the variable SKEW_CN is not greater than SKEW_REF 1  which is a skew reference value 1 (i.e. SKEW_CN≦SKEW_REF 1 ). If the value of the variable SKEW_CN is not greater than SKEW_REF 1  which is the skew reference value 1 (i.e. SKEW_CN≦SKEW_REF 1 ), the CPU circuit section  560  immediately terminates the present process. 
   If, as a result of the determination in the step S 2310 , the value of the variable SKEW_CN is greater than SKEW_REF 2  which is a skew reference value 2 (i.e. SKEW_CN&lt;SKEW_REF 2 ), the CPU circuit section  560  sets an inserter skew jam, i.e. stops all the loads. It should be noted that the skew reference value 2 is a lower limit of skew amount at which jamming may occur during conveyance of a sheet. The CPU circuit section  560  then inhibits sheet conveyance in the finisher  500 , punching on sheets by the punch unit  550 , stapling by the stapler  601 , and so forth. Further, the CPU circuit section  560  transmits an emergency stop signal which prompts the CPU circuit section  150  of the copying apparatus  1000  to carry out an emergency stop process to the CPU circuit section  150  so as to urgently stop conveying sheets in the printer section  300  (step S 2311 ) and terminates the present process. 
   Upon receiving the emergency stop signal, the CPU circuit section  150  displays a message indicating the receipt of the emergency stop signal on the display panel of the operating section  1  so as to inform the user to that effect. Further, the CPU circuit section  150  urgently stops the conveyance of a sheet with an image formed thereon so as to inhibit the sheet from being conveyed into the finisher  500 . 
   The CPU circuit section  560  inhibits all of the above described operations in the finisher  500  until the user completely removes the sheet. When the removal of the sheet is completed, the CPU circuit section  560  cancels the inhibition of the operations in the finisher  500  and informs the CPU circuit section  150  of the copying apparatus  1000  that the emergency stop has been canceled. 
   When informed that the emergency stop has been canceled, the CPU circuit section  150  displays a message indicating the cancellation of the emergency stop signal on the display panel of the operating section  1  so as to inform the user to that effect. 
   If, as a result of the determination in the step S 2310 , the value of the variable SKEW_CN is greater than SKEW_REF 1  and not greater than SKEW_REF 2 , the CPU circuit section  560  determines whether or not the set operation mode is the punch mode (step S 2312 ). If the set operation mode is any mode other than the punch mode, the CPU circuit section  560  immediately terminates the present process without stopping all the loads, and if the set operation mode is the punch mode, the CPU circuit section  560  sets an inserter skew jam as in the step S 2311  and terminates the present process. 
   If the operation mode set by the user is any mode other than the punch mode, e.g. the staple mode, the CPU circuit section  560  carries out the stapling process after aligning the sheets conveyed to the processing tray  630 . If the operation mode set by the user is the bookbinding mode, the CPU circuit section  560  carries out the bookbinding process after aligning the sheets conveyed to the housing guide  820 . Thus, the value of the detected skew amount SKEW_CN does not influence the final sheet alignment quality in binding. On the other hand, if the operation mode set by the user is the punch mode, the CPU circuit section  560  carries out the punching process without aligning the sheets conveyed in the finisher  500 . Thus, the sheets are not punched at correct positions, and therefore, the sheet alignment quality is degraded. 
   For this reason, the CPU circuit section  560  determines in the step S 2312  whether or not the operation mode set by the user is the punch mode, and whether or not the CPU circuit section  560  stops all the loads is controlled according to the determination result. 
   According to the process in  FIG. 24 , the CPU circuit section  560  sets an inserter skew jam, i.e. stops all the loads when the value of the variable SKEW_CN is greater than SKEW_REF 2  (step S 2311 ). Also, the CPU circuit section  560  immediately terminates the present process without stopping all the loads when the value of the variable SKEW_CN is greater than SKEW_REF 1  and not greater than SKEW_REF 2  and the set operation mode is any mode other than the punch mode (“NO” to the step S 2312 ). Also, if the set operation mode is the punch mode (“YES” to the step S 2312 ), the CPU circuit section  560  sets an inserter skew jam (step S 2313 ). For example, suppose that SKEW_REF 1  is 3 mm, and SKEW_REF 2  is 9 mm. In this case, if the skew amount of an insert sheet detected by the skew sensors  930  and  931  is greater than 9 mm, there is a possibility that sheet jamming occurs. Thus, the CPU circuit section  560  urgently stops the conveyance of the sheet and inhibits feeding, conveyance, punching, etc. of the sheet. If the detected skew amount of an insert is not greater than 3 mm, the CPU circuit section  560  does not urgently stop the conveyance of the sheet and permits feeding, conveyance, punching, etc. of the sheet. If the detected skew amount of an insert is greater than 3 mm and not greater than 9 mm and the punch mode has been set in advance by the user, the CPU circuit section  560  urgently stops the conveyance of the sheet and inhibits feeding, conveyance, punching, etc. of the sheet. 
   In this way, the CPU circuit section  560  can send an emergency stop signal to the CPU circuit section  150  of the copying apparatus  1000  before sheet jamming actually occurs, and therefore it is possible to prevent the sheet quality from being degraded. 
   Also, in the case where the CPU circuit section  560  stops all the loads by setting an inserter skew jam, the user removes a sheet from the finisher  500  and then places the sheet on the insert tray  901  of the inserter  500  again. Thereafter, by giving an instruction for resuming processing via the operating section  1 , the user can reuse the sheet. Thus, it is possible to prevent damages to sheets, contamination of sheets, etc. caused by sheet jamming. Thus, the user does not have to prepare the same sheets again, and the user&#39;s trouble and effort can be saved. 
   Further, the CPU circuit section  560  immediately terminates the present process without stopping all the loads and continues conveying sheets when the value of the variable SKEW_CN is greater than SKEW_REF 1  and not greater than SKEW_REF 2  and the set operation mode is any mode other than the punch mode. Thus, it is possible to prevent unnecessary stop of all the loads and improve user&#39;s productivity. 
     FIG. 25  is a flow chart showing the procedure of a sheet information setting process for sheets stacked on the insert tray appearing in  FIG. 5 . 
   As shown in  FIG. 25 , the CPU circuit section  560  determines whether or not sheets are stacked using a sheet set sensor, not shown, on the insert tray  901  (step S 2401 ) If the sheets are stacked, the CPU circuit section  560  causes a “sheet size selection” screen ( FIG. 26 ) to be displayed on the display panel of the operating section  1  (step S 2403 ) and determines whether or not the size has been determined (step S 2405 ). The CPU circuit section  560  repeatedly carries out the above determination until the size is determined, and when the size is determined, the CPU circuit section  560  causes a “sheet type selection” screen ( FIG. 27 ) to be displayed on the display panel (step S 2407 ) and determines whether or not the sheet type has been determined. The CPU circuit section repeatedly carries out the above determination until the sheet type is determined, and when the sheet type is determined, the CPU circuit section  560  determines whether or not the sheet type is a special type (step S 2411 ). If the sheet type is a special type, the CPU circuit section  560  turns on a special sheet flag “special_material_flg” (step S 2415 ). If the sheet type is a special type, the CPU circuit section  560  turns off the special sheet flag “special_material_flg” (step S 2413 ) and goes to a step S 2417 . 
   Next, in the step S 2417 , the CPU circuit section  560  causes a “sheet orientation selection” screen ( FIG. 28 ) to be displayed on the display panel and determines whether or not the special sheet flag “special_material_flg” is on (step S 2419 ). If the special sheet flag “special_material_flg” is off, the CPU circuit section  560  turns off an inverted sheet feed alarm flag “rev_set_alarm_flg” (step S 2422 ) ( FIG. 28 ) and goes to a step S 2425 , described later. If the special sheet flag “special_material_flg” is on, the CPU circuit section  560  checks the status of the “sheet orientation selection” screen ( FIG. 29 ) to determine whether or not a back cover is designated (step S 2421 ). If a back cover is designated, the CPU circuit section  560  carries out the processing in the step S 2422 , and if a back cover is not designated, the CPU circuit section  560  causes an alarm and a user guide to be displayed on the display panel (step S 2423 ) ( FIG. 28 ), and goes to the step S 2425 , described later. In the user guide, a possibility that a sheet of the determined sheet type is not properly inserted into a sheet bundle discharged from the printer section  300  is written so as to prompt the user to confirm and change the orientations (front and back sides) of sheets stacked on the insert tray  901 . This can prevent troubles such as sheet buckling and jamming. 
   Next, in the step S 2425 , the CPU circuit section  560  determines whether or not the sheet orientation has been determined. If the sheet orientation has been determined, the CPU circuit section  560  determines whether or not the inverted sheet feed alarm flag “rev_set_alarm_flg” is on (step S 2427 ). If the inverted sheet feed alarm flag “rev_set_alarm_flg” is off, the CPU circuit section  560  immediately terminates the present process, and if the inverted sheet feed alarm flag “rev_set_alarm_flg” is on, the CPU circuit section  560  inhibits inverted sheet discharge (step S 2429 ) and terminates the present process. 
   According to the process in  FIG. 25 , if a special sheet type has been designated and a back cover has not been designated, the CPU circuit section  560  displays the alarm and the user guide on the display panel and inhibits inverted sheet discharge. Thus, sheets of a special type such as thick sheets can be inhibited from passing through the inversion path  955  which is intended to invert sheets, and there is no need to increase the curve of the inversion path  955 . It is therefore possible to downsize the apparatus and prevent buckling, jamming, etc. of special type sheets. In many cases, a sheet supplied from the inserter  900  is a value-added sheet or a sheet on which an image cannot be easily formed by the copying apparatus  1000 ; e.g. a sheet with an image such as a photograph formed thereon, the front cover of a catalogue, a calendared sheet, and a colored sheet. In such cases, the above described effects can be enhanced. 
   It is to be understood that the object of the present invention may also be accomplished by supplying a system or an apparatus with a storage medium in which a program code of software, which realizes the functions of the above described embodiment is stored, and causing a computer (or CPU or MPU) of the system or apparatus to read out and execute the program code stored in the storage medium. 
   In this case, the program code itself read from the storage medium realizes the functions of the above described embodiment, and hence the program code and the storage medium in which the program code is stored constitute the present invention. 
   Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, a magnetic-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAM, a DVD-RW, and a DVD+RW, a magnetic tape, a nonvolatile memory card, and a ROM. Alternatively, the program code may be downloaded via a network. 
   Further, it is to be understood that the functions of the above described embodiment may be accomplished not only by executing a program code read out by a computer, but also by causing an OS (operating system) or the like which operates on the computer to perform a part or all of the actual operations based on instructions of the program code. 
   Further, it is to be understood that the functions of the above described embodiment may be accomplished by writing a program code read out from the storage medium into a memory provided on an expansion board inserted into a computer or in an expansion unit connected to the computer and then causing a CPU or the like provided in the expansion board or the expansion unit to perform a part or all of the actual operations based on instructions of the program code. 
   This application claims priority from Japanese Patent Application No. 2005-285059 filed Sep. 29, 2005, which is hereby incorporated by reference herein in its entirety.