Patent Publication Number: US-9891571-B2

Title: Post-processing device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-236560 filed Dec. 3, 2015. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a post-processing device and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided a post-processing device including a processing stacking portion that allows plural media transported from an upstream side to be stacked thereon; a binding member that performs a binding process on the media stacked on the processing stacking portion; a medium ejection portion on which the media ejected from the processing stacking portion are stacked, the medium ejection portion moving upward and downward in accordance with an amount of the media stacked on the medium ejection portion; and a pressing member that presses an upper surface of the media stacked on the medium ejection portion. When media that have not been subjected to the binding process are stacked on the medium ejection portion, the pressing member and the media on the medium ejection portion are brought into contact with each other, and when media that have been subjected to the binding process are stacked on the medium ejection portion, the pressing member and the media on the medium ejection portion are disposed further away from each other than when media that have not been subjected to the binding process are stacked on the medium ejection portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  illustrates the overall structure of an image forming apparatus according to a first exemplary embodiment of the present invention; 
         FIG. 2  illustrates a visual-image forming member including an image carrier unit and a developing device according to the first exemplary embodiment of the present invention; 
         FIG. 3  illustrates a post-processing device according to the first exemplary embodiment of the present invention; 
         FIG. 4  illustrates how a clamping roller moves in an edge binding device according to the first exemplary embodiment of the present invention; 
         FIG. 5  illustrates how a second paddle wheel moves in the edge binding device according to the first exemplary embodiment of the present invention; 
         FIG. 6  illustrates a clamping member according to the first exemplary embodiment of the present invention; 
         FIG. 7  is a block diagram illustrating functions of a control section of the image forming apparatus according to the first exemplary embodiment; 
         FIG. 8  is a block diagram that continues from the block diagram illustrated in  FIG. 7  and illustrates functions of the control section of the image forming apparatus according to the first exemplary embodiment; 
         FIG. 9  is a flowchart of a stacker-tray raising-lowering process according to the first exemplary embodiment; 
         FIG. 10  is a flowchart of a clamping-member controlling process according to the first exemplary embodiment; 
         FIGS. 11A to 11C  illustrate an aligning mode according to the first exemplary embodiment, where  FIG. 11A  illustrates a state before the start of ejection of a sheet stack to a stacker tray,  FIG. 11B  illustrates a state in which the ejection of the sheet stack to the stacker tray is performed after the state of  FIG. 11A , and  FIG. 11C  illustrates a state in which the sheet stack has passed a compile sensor after the state of  FIG. 11B ; 
         FIGS. 12A to 12C  illustrate a stapling mode according to the first exemplary embodiment, where  FIG. 12A  illustrates a state before the start of ejection of a sheet stack to the stacker tray,  FIG. 12B  illustrates a state in which the ejection of the sheet stack to the stacker tray is performed after the state of  FIG. 12A , and  FIG. 12C  illustrates a state in which the sheet stack has passed a compile sensor after the state of  FIG. 12B ; 
         FIG. 13  illustrates a clamping member according to a second exemplary embodiment of the present invention, and corresponds to  FIG. 6  illustrating the first exemplary embodiment; 
         FIG. 14  is a block diagram illustrating functions of a control section of an image forming apparatus according to the second exemplary embodiment; 
         FIG. 15  is a block diagram that continues from the block diagram illustrated in  FIG. 14  and illustrates functions of the control section of the image forming apparatus according to the second exemplary embodiment; 
         FIG. 16  is a flowchart of a stacker-tray raising-lowering process according to the second exemplary embodiment, and corresponds to  FIG. 9  illustrating the first exemplary embodiment; and 
         FIG. 17  is a flowchart of a clamping-member controlling process according to the second exemplary embodiment, and corresponds to  FIG. 10  illustrating the first exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following exemplary embodiments. 
     To facilitate understanding of the following description, in each figure, the front-back direction, the left-right direction, and the up-down direction are defined as the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. In addition, the directions shown by arrows X, −X, Y, −Y, Z, and −Z are defined as forward, backward, rightward, leftward, upward, and downward, respectively, and sides in those directions are defined as the front side, the back side, the right side, the left side, the top side, and the bottom side, respectively. 
     In the figures, circles having dots at the center show the direction from back to front with respect to the sides illustrated in the figures, and circles having the “X” marks therein show the direction from front to back with respect to the sides illustrated in the figures. 
     In each figure, components other than those necessary for explanation are omitted to facilitate understanding. 
     First Exemplary Embodiment 
     Overall Structure of Printer U of First Exemplary Embodiment 
       FIG. 1  illustrates the overall structure of an image forming apparatus according to a first exemplary embodiment of the present invention. 
     In  FIG. 1 , a printer U, which is an example of an image forming apparatus according to the first exemplary embodiment, includes a scanner unit U 1  as an example of an image-information reading device. A sheet feeding device U 2 , which is an example of a medium supplying device, is provided below the scanner unit U 1 . A printer body U 3 , which is an example of an image forming apparatus body, is disposed on the right side of the sheet feeding device U 2 . A finisher U 4 , which is an example of a post-processing device, is disposed on the right side of the printer body U 3 . A user interface UI, which is an example of an operation unit, is supported at a location above the sheet feeding device U 2 . 
     The user interface UI includes a display panel UI 1  as an example of a display, and an input button unit including a copy start key, numeric keys, and a copy-number input key. 
     The scanner unit U 1  includes a document feeder U 1   a  as an example of a document transporting device, and an image scanner U 1   b  as an example of an image reading unit. 
     The sheet feeding device U 2  includes plural sheet feeding trays TR 1  to TR 4  as examples of medium containers. Each of the sheet feeding trays TR 1  to TR 4  contains sheets S as examples of media. A supply path SH 1 , which is an example of a transport path, is provided in the sheet feeding device U 2 . The supply path SH 1  connects the sheet feeding trays TR 1  to TR 4  to the printer body U 3 . 
     Structure of Image Recording Unit U 3   a  of First Exemplary Embodiment 
     In  FIG. 1 , the printer body U 3  includes an image recording unit U 3   a  that records an image on a sheet S. A toner dispenser U 3   b , which is an example of a developer supplying device, is disposed above the image recording unit U 3   a.    
     The printer body U 3  includes a controller C as an example of a control section. The controller C is electrically connected to a client personal computer PC, which is an example of an image information transmitter. The controller C receives image information or the like transmitted from the client personal computer PC. The controller C controls a laser driving circuit D, which is an example of an exposure-device driving circuit, and a power supply circuit E. 
     The laser driving circuit D outputs signals of image information for respective colors, which are yellow (Y), magenta (M), cyan (C), and black (K), to exposure devices ROSy, ROSm, ROSc, and ROSk for the respective colors Y, M, C, and K on the basis of the information input from the scanner unit U 1  or the client personal computer PC at a preset timing. 
     A drawer member U 3   c  of an image forming unit is supported below the exposure devices ROSy, ROSm, ROSc, and ROSk for the respective colors Y, M, C, and K. The drawer member U 3   c  of the image forming unit is supported by a pair of left and right guiding members R 1  and R 1  such that the drawer member U 3   c  is moveable between a position in front of the printer body U 3  to which the drawer member U 3   c  is drawn and a position at which the drawer member U 3   c  is installed in the printer body U 3 . 
       FIG. 2  illustrates a visual-image forming member including an image carrier unit and a developing device according to the first exemplary embodiment of the present invention. 
     Referring to  FIGS. 1 and 2 , photoconductors Py, Pm, Pc, and Pk, which are examples of image carriers, are disposed below the respective exposure devices ROSy, ROSm, ROSc, and ROSk. In the first exemplary embodiment, the black (K) photoconductor Pk, which is frequently used and whose surface easily wears, has a diameter greater than those of the photoconductors Py, Pm, and Pc for the other colors Y, M, and C. Accordingly, the black (K) photoconductor Pk is rotatable at a high speed, and has a long lifespan. 
     A charger CCk, which is an example of a charging device, is disposed above the black (K) photoconductor Pk. A developing device Gk is disposed downstream of the charger CCk in a rotational direction in which the photoconductor Pk rotates. The developing device Gk includes a developing roller R 0  as an example of a developer carrier. A first transfer roller T 1   k , which is an example of a first transfer device, is disposed downstream of the developing device Gk in the rotational direction of the photoconductor Pk. A cleaner CLk, which is an example of a photoconductor cleaning device, is disposed downstream of the first transfer roller T 1   k  in the rotational direction of the photoconductor Pk. 
     The photoconductor Pk, the charger CCk, and the cleaner CLk form a black (K) photoconductor unit Uk as an example of an image carrier unit according to the first exemplary embodiment. Therefore, the photoconductor Pk, the charger CCk, and the cleaner CLk are formed integrally with each other and are detachably attached to the printer body U 3 . Similarly to the black (K) photoconductor unit Uk, photoconductor units Uy, Um, and Uc for the other colors are formed of photoconductors Py, Pm, and Pc, chargers CCy, CCm, and CCc, and cleaners CLy, CLm, and CLc. 
     The photoconductor units Uy, Um, Uc, and Uk and the developing devices Gy, Gm, Gc, and Gk constitute visible-image forming members Uy+Gy, Um+Gm, Uc+Gc, and Uk+Gk according to the first exemplary embodiment. The photoconductor units Uy, Um, Uc, and Uk and the developing devices Gy, Gm, Gc, and Gk are detachably attached to the above-described drawer member U 3   c  of the image forming unit. 
     A drawer member U 3   d  of an intermediate transfer body is supported below the drawer member U 3   c  of the image forming unit. The drawer member U 3   d  of the intermediate transfer body is supported such that the drawer member U 3   d  is moveable between a position in front of the printer body U 3  to which the drawer member U 3   d  is drawn and a position at which the drawer member U 3   d  is installed in the printer body U 3 . A belt module BM, which is an example of an intermediate transfer device, is supported by the drawer member U 3   d  of the intermediate transfer body. The belt module BM is supported such that the belt module BM is movable upward and downward between a position at which the belt module BM is in contact with the bottom surfaces of the photoconductors Py, Pm, Pc, and Pk and a position at which the belt module BM is below the bottom surfaces of the photoconductors Py, Pm, Pc, and Pk. 
     The belt module BM includes an intermediate transfer belt B, belt support rollers Rd, Rt, Rw, Rf, and T 2   a , which are examples of intermediate-transfer-body support members, and first transfer rollers T 1   y , T 1   m , T 1   c , and T 1   k . The belt support rollers Rd, Rt, Rw, Rf, and T 2   a  include a belt driving roller Rd, which is an example of an intermediate-transfer-body driving member; a tension roller Rt, which is an example of a tension applying member; a walking roller Rw, which is an example of a meandering preventing member; plural idler rollers Rf, which are examples of driven members; and a backup roller T 2   a , which is an example of an opposing member for a second transfer process. The intermediate transfer belt B is supported by the belt support rollers Rd, Rt, Rw, Rf, and T 2   a  such that the intermediate transfer belt B is rotatable in the direction of arrow Ya. 
     A belt cleaner CLB, which is an example of an intermediate-transfer-body cleaning device, is disposed near the belt driving roller Rd. 
     A second transfer unit Ut is disposed below the backup roller T 2   a . The second transfer unit Ut includes a second transfer roller T 2   b  as an example of a second transfer member. The region in which the second transfer roller T 2   b  is in contact with the intermediate transfer belt B serves as a second transfer region Q 4 , which is an example of an image recording region. A contact roller T 2   c , which is an example of a voltage-applying contact member, is in contact with the backup roller T 2   a . A second transfer voltage having the same polarity as the charging polarity of the toner is applied to the contact roller T 2   c  by the power supply circuit E, controlled by the controller C, at a preset timing. 
     The backup roller T 2   a , the second transfer roller T 2   b , and the contact roller T 2   c  form a second transfer device T 2  according to the first exemplary embodiment. The first transfer rollers T 1   y , T 1   m , T 1   c , and T 1   k , the intermediate transfer belt B, and the second transfer device T 2  constitute a transferring device T 1 +B+T 2  according to the first exemplary embodiment which transfers the images on the surfaces of the photoconductors Py to Pk onto the sheet S. 
     A feeding path SH 2 , which is an example of a transport path, is disposed below the belt module BM. The feeding path SH 2  extends from the supply path SH 1  of the sheet feeding device U 2  toward the second transfer region Q 4 . Plural transport rollers Ra, which are examples of medium transporting members, are arranged along the feeding path SH 2 . In addition, a registration roller Rr is provided on the feeding path SH 2  at a location upstream of the second transfer region Q 4  in the transporting direction of the sheet S. The registration roller Rr is an example of an adjusting member that adjust a transport timing at which the sheet S is transported to the second transfer device T 2 . A guiding member SGr for guiding the medium is disposed downstream of the registration roller Rr in the transporting direction of the sheet S. The guiding member SGr for the medium is fixed to the printer body U 3  together with the registration roller Rr. A guiding member SG 1  for guiding the medium before the transfer process is disposed between the guiding member SGr for the medium and the second transfer region Q 4 . 
     A guiding member SG 2  for guiding the medium after the transfer process is disposed downstream of the second transfer region Q 4  in the transporting direction of the sheet S. A transporting belt BH, which is an example of a medium transporting member, is disposed downstream of the guiding member SG 2  for guiding the medium after the transfer process in the transporting direction of the sheet S. A fixing device F is disposed downstream of the transporting belt BH in the transporting direction of the sheet S. The fixing device F includes a heating roller Fh, which is an example of a heating fixing member, and a pressing roller Fp, which is an example of a pressing fixing member. The region in which the heating roller Fh and the pressing roller Fp are in contact with each other serves as a fixing region Q 5 . 
     The visible-image forming members Uy+Gy to Uk+Gk, the transferring device T 1 +B+T 2 , and the fixing device F constitute the image recording unit U 3   a  according to the first exemplary embodiment. 
     An ejection path SH 3 , which is an example of a transport path, is disposed downstream of the fixing device F in the transporting direction of the sheet S. The ejection path SH 3  extends rightward and upward from the downstream end of the feeding path SH 2  in the transporting direction of the sheet S. The transport rollers Ra are arranged along the ejection path SH 3 . An ejection roller Rh, which is an example of a medium ejecting member, is disposed at the downstream end of the ejection path SH 3  in the transporting direction of the sheet S. 
     An upstream end of a reversing path SH 4 , which is an example of a transport path, in the transporting direction of the sheet S is connected to a connecting portion between the feeding path SH 2  and the ejection path SH 3 . The reversing path SH 4  extends downward. Reversing rollers Rb, which are examples of medium reversing members and which are rotatable in forward and reverse directions, are arranged along the reversing path SH 4 . An upstream end of an ejecting-reversing path SH 5 , which is an example of a transport path, in the transporting direction of the sheet S is connected to the reversing path SH 4  at an intermediate position thereof. The downstream end of the ejecting-reversing path SH 5  in the transporting direction of the sheet S is connected to the ejection path SH 3 . An upstream end of a circulation path SH 6 , which is an example of a transport path, in the transporting direction of the sheet S is connected to the reversing path SH 4  at an intermediate position thereof that is downstream of the position at which the reversing path SH 4  is connected to the ejecting-reversing path SH 5  in the transporting direction of the sheet S. The circulation path SH 6  connects the reversing path SH 4  to the supply path SH 1  of the sheet feeding device U 2 . Transport rollers Ra are arranged along the circulation path SH 6 . 
     A switching gate GT 1 , which is an example of a destination switching member, is provided on a connecting portion between the feeding path SH 2  and the ejection path SH 3 . 
     A Mylar gate GT 2 , which is an example of a transporting-direction regulating member, is provided on a connecting portion between the reversing path SH 4  and the ejecting-reversing path SH 5 . 
     A Mylar gate GT 3 , which is also an example of a transporting-direction regulating member, is provided on a connecting portion between the reversing path SH 4  and the circulation path SH 6 . 
     Elements denoted by SH 1  to SH 6  constitute a transporting path body SH according to the first exemplary embodiment. 
     Operation of Image Recording Unit U 3   a  of First Exemplary Embodiment 
     When the controller C receives image information from the client personal computer PC or the scanner unit U 1 , the printer U starts a job, that is, an image forming operation. When the job is started, the photoconductors Py to Pk, the intermediate transfer belt B, and other components start to rotate. 
     The chargers CCy to CCk receive a preset voltage from the power supply circuit E, and charge the surfaces of the photoconductors Py to Pk. 
     The exposure devices ROSy to ROSk output laser beams Ly, Lm, Lc, and Lk, which are examples of latent-image-writing light, on the basis of signals from the laser driving circuit D. The surfaces of the photoconductors Py to Pk are irradiated with the laser beams Ly to Lk so that electrostatic latent images are formed thereon. 
     The developing rollers R 0  of the developing devices Gy to Gk develop the electrostatic latent images on the surfaces of the photoconductors Py to Pk into visible images. 
     The toner dispenser U 3   b  supplies developers to the developing devices Gy to Gk when the developers in the developing devices Gy to Gk are consumed. 
     The power supply circuit E applies a first transfer voltage to the first transfer rollers T 1   y  to T 1   k , the first transfer voltage having a polarity opposite to the charging polarity of the developers. Thus, the visible images on the surfaces of the photoconductors Py to Pk are transferred onto the surface of the intermediate transfer belt B. 
     The cleaners CLy to CLk clean the surfaces of the photoconductors Py to Pk by removing the developers that remain thereon after the first transfer process. 
     Y, M, C, and K images are transferred onto the intermediate transfer belt B in that order in a superimposed manner when the intermediate transfer belt B passes through the first transfer regions Q 3   y  to Q 3   k  that face the photoconductors Py to Pk, respectively. Then, the intermediate transfer belt B passes through the second transfer region Q 4  that faces the second transfer device T 2 . When a monochrome image is to be formed, a single colored image is transferred onto the intermediate transfer belt B, and then the intermediate transfer belt B passes through the second transfer region Q 4 . 
     The sheet feeding trays TR 1  to TR 4  contain sheets S. A sheet S contained in one of the sheet feeding trays TR 1  to TR 4  is transported along the supply path SH 1  of the sheet feeding device U 2  by the transport rollers Ra, and fed to the feeding path SH 2  of the printer body U 3 . 
     The sheet S fed to the feeding path SH 2  is transported toward the registration roller Rr. 
     The registration roller Rr feeds the sheet S toward the second transfer region Q 4  at the time when the image on the surface of the intermediate transfer belt B is transported to the second transfer region Q 4 . 
     In the second transfer device T 2 , the power supply circuit E applies a second transfer voltage to the backup roller T 2   a  through the contact roller T 2   c . The second transfer voltage has the same polarity as the preset charging polarity of the developers. Therefore, the image on the intermediate transfer belt B is transferred onto the sheet S that passes through the second transfer region Q 4 . 
     The belt cleaner CLB cleans the surface of the intermediate transfer belt B by removing the developers that remain thereon after the image has been transferred in the second transfer region Q 4 . 
     The transporting belt BH holds the sheet S, onto which the image has been transferred by the second transfer device T 2 , on the surface thereof and transports the sheet S to the fixing device F. 
     The fixing device F heats the sheet S that passes through the fixing region Q 5  while applying a pressure to the sheet S. Accordingly, the unfixed image on the surface of the sheet S is fixed to the sheet S. The sheet S to which the image has been fixed is transported to the downstream end of the feeding path SH 2  in the transporting direction of the sheet S. 
     The switching gate GT 1  at the downstream end of the feeding path SH 2  in the transporting direction of the sheet S switches the destination of the sheet S between the ejection path SH 3  and the reversing path SH 4 . 
     When the sheet S is to be ejected in a reversed manner or when double-sided printing is to be performed, the destination of the sheet S having an image recorded on one side thereof is switched to the reversing path SH 4 . Accordingly, the sheet S is transported to the reversing path SH 4 . The sheet S is transported along the reversing path SH 4  by the reversing rollers Rb and passes through the Mylar gate GT 2 . 
     When the sheet S is to be ejected in a reversed state, the reversing rollers Rb start to rotate in the reverse direction after the upstream end of the sheet S in the transporting direction of the sheet S has passed the Mylar gate GT 2 . Accordingly, the sheet S is transported in the reverse direction in a so-called switchback manner. When double-sided printing is to be performed, the reversing rollers Rb start to rotate in the reverse direction after the upstream end of the sheet S in the transporting direction of the sheet S has passed the Mylar gate GT 2  and the Mylar gate GT 3 , so that the sheet S is transported in the switchback manner. 
     The Mylar gate GT 2  allows the sheet S that has been transported along the reversing path SH 4  to pass therethrough. Then, the Mylar gate GT 2  regulates the transporting direction of the sheet S transported in a switchback manner so as to guide the sheet S to the ejecting-reversing path SH 5 . Accordingly, the sheet S is guided from the ejecting-reversing path SH 5  to the ejection path SH 3 . 
     The Mylar gate GT 3  allows the sheet S that has been transported along the reversing path SH 4  to pass therethrough. Then, the Mylar gate GT 3  regulates the transporting direction of the sheet S transported in a switchback manner to guide the sheet S to the circulation path SH 6 . 
     The sheet S that has been transported to the circulation path SH 6  is transported to the supply path SH 1  in the sheet feeding device U 2 . Thus, the sheet S transported in the switchback manner is transported from the supply path SH 1  to the registration roller Rr on the feeding path SH 2  again in a reversed state. Accordingly, an image is recorded on a second side of the sheet S. 
     When the sheet S on which an image is recorded is ejected from the printer body U 3 , the destination of the sheet S is switched to the ejection path SH 3 . Accordingly, the sheet S having the image recorded thereon is guided to the ejection path SH 3 . The sheet S is transported along the ejection path SH 3  by the transport rollers Ra, and ejected from the printer body U 3  by the ejection roller Rh. 
     Structure of Finisher U 4  of First Exemplary Embodiment 
       FIG. 3  illustrates a post-processing device according to the first exemplary embodiment of the present invention. 
     In  FIGS. 1 and 3 , the finisher U 4 , which is an example of a post-processing device, is disposed on the right side of the printer body U 3 . The finisher U 4  includes a feeding path SH 11 , which is an example of a transport path. The feeding path SH 11  extends into the finisher U 4  from the downstream end of the ejection path SH 3  of the printer body U 3  in the transporting direction of the sheet S. An upstream end of a relay path SH 12 , which is an example of a transport path and which extends rightward, in the transporting direction of the sheet S is connected to the downstream end of the feeding path SH 11  in the transporting direction of the sheet S. An upstream end of a saddle-stitching transport path SH 13 , which is an example of a transport path and which extends downward, in the transporting direction of the sheet S is also connected to the downstream end of the feeding path SH 11  in the transporting direction of the sheet S. 
     An upstream end of an ejection path SH 14 , which is an example of a transport path and which extends upward, in the transporting direction of the sheet S is connected to the downstream end of the relay path SH 12  in the transporting direction of the sheet S. An upstream end of an edge-binding transport path SH 15 , which is an example of a transport path and which extends rightward, in the transporting direction of the sheet S is connected to the downstream end of the relay path SH 12  in the transporting direction of the sheet S. 
     A first gate GT 11 , which is an example of a destination switching member, is provided at a branching portion between the relay path SH 12  and the saddle-stitching transport path SH 13 . 
     A second gate GT 12 , which is also an example of a destination switching member, is provided at a branching portion between the ejection path SH 14  and the edge-binding transport path SH 15 . 
     An ejection roller Rh 1 , which is an example of an ejecting member, is arranged at the downstream end of the ejection path SH 14  in the transporting direction of the sheet S. A top tray TH 0 , which is an example of a medium receiver, is supported at a location downstream of the ejection roller Rh 1  in an ejecting direction in which the sheet S is ejected. 
     An edge binding device HTS is disposed downstream of the edge-binding transport path SH 15  in the transporting direction of the sheet S. The edge binding device HTS may have a well-known structure as those described in, for example, Japanese Unexamined Patent Application Publication Nos. 2003-089462, 2003-089463, 2006-69746, or 2006-69749, and detailed description of the edge binding device HTS is thus omitted. A stacker tray TH 1 , which is an example of an edge-binding receiver, is supported at a location downstream of the edge binding device HTS in the transporting direction of the sheet S. The stacker tray TH 1  is supported in a vertically movable manner. 
     A saddle stitching device NTS is disposed downstream of the saddle-stitching transport path SH 13  in the transporting direction of the sheet S. A saddle-stitching stacker tray TH 2 , which is an example of a saddle-stitching receiver, is supported at a location downstream of the saddle stitching device NTS in the transporting direction of the sheet S. 
     Operation of Finisher U 4  of First Exemplary Embodiment 
     The sheet S transported from the printer body U 3  is fed to the feeding path SH 11  of the finisher U 4 . The sheet S fed to the feeding path SH 11  is transported to the first gate GT 11 . 
     The first gate GT 11  switches the destination of the sheet S between the relay path SH 12  and the saddle-stitching transport path SH 13  depending on the settings regarding post-processing. 
     The sheet S fed to the relay path SH 12  is transported to the second gate GT 12 . 
     The second gate GT 12  switches the destination of the sheet S between the ejection path SH 14  and the edge-binding transport path SH 15  depending on the settings regarding post-processing. 
     The sheet S fed to the ejection path SH 14  is ejected to the top tray TH 0  by the ejection roller Rh 1 . 
     The sheet S fed to the edge-binding transport path SH 15  is transported to the edge binding device HTS. 
     The edge binding device HTS aligns the edges of plural sheets S and binds the edges of the sheets S together. The stack of sheets S processed by the edge binding device HTS is ejected to the stacker tray TH 1 . 
     When the stack of sheets S is placed on the stacker tray TH 1 , the stacker tray TH 1  moves downward depending on the number of sheets S placed thereon. 
     The sheet S fed to the saddle-stitching transport path SH 13  is transported to the saddle stitching device NTS. 
     The saddle stitching device NTS processes a stack of sheets S so as to bind the sheets S together at the center thereof in the transporting direction of the sheets S. The saddle stitching device NTS folds the stack of bound sheets S in half at the center and ejects the folded stack of sheets S to the saddle-stitching stacker tray TH 2 . 
     Details of Edge-Binding Transport Path of First Exemplary Embodiment 
       FIG. 4  illustrates how a clamping roller  12  moves in the edge binding device HTS according to the first exemplary embodiment of the present invention. 
       FIG. 5  illustrates how a second paddle wheel  13  moves in the edge binding device HTS according to the first exemplary embodiment of the present invention. 
     Referring to  FIGS. 4 and 5 , an exit roller Rh 2 , which is an example of an ejecting member and is also an example of a feeding member, is disposed at the downstream end of the edge-binding transport path SH 15  in the transporting direction of the sheets S. An exit sensor SN 1 , which is an example of a medium detecting member, is disposed upstream of the exit roller Rh 2  in the transporting direction of the sheets S. 
     Details of Edge Binding Device of First Exemplary Embodiment 
     Referring to  FIGS. 4 and 5 , the edge binding device HTS is disposed downstream of the exit roller Rh 2  in the transporting direction of the sheets S. 
     The edge binding device HTS includes a compiler tray  1  as an example of a processing stacking portion. The compiler tray  1  has a stacking surface  1   a  on which the sheets S are stacked. The stacking surface  1   a  is slightly inclined with respect to the horizontal direction so as to extend rightward and upward. 
     A pair of tampers  2  and  3 , which are examples of aligning members for aligning the edges of media in the width direction, are provided on the compiler tray  1 . The tampers  2  and  3  are arranged in the front-back direction, and are supported so as to be movable in the front-back direction. Accordingly, the tampers  2  and  3  are movable toward and away from each other. 
     An end wall  4 , which is an example of an aligning member for aligning the edges of the media in the transporting direction thereof, is supported on a lower left portion of the compiler tray  1 . The end wall  4  includes a positioning wall  4   a  that stands on the stacking surface  1   a  of the compiler tray  1 , and a guide wall  4   b  that extends upward and rightward from the top edge of the positioning wall  4   a.    
     A first paddle wheel  6 , which is an example of a first drawing member, is supported above the end wall  4 . The first paddle wheel  6  is rotatably supported. The first paddle wheel  6  includes flexible sheet contact portions  6   a  that extend radially outward. The sheet contact portions  6   a  are capable of coming into contact with the sheets S on the compiler tray  1 . The first paddle wheel  6  receives a driving force from a driving source (not shown). 
     A stapler guide  7 , which is an example of a binding-member guide, is supported in a region below and on the left side of the end wall  4 . The stapler guide  7  extends parallel to the end wall  4  in the front-back direction. 
     A stapler  8 , which is an example of a binding member, is supported by the stapler guide  7 . The stapler  8  is moveable along the stapler guide  7 . Thus, the stapler  8  is supported so as to be moveable parallel to the end wall  4  in the front-back direction. 
     An ejection shaft  9 , which extends in the front-back direction, is provided at the upper right end of the compiler tray  1 . The ejection shaft  9  is rotatably supported. The ejection shaft  9  supports an ejecting roller  11 , which is an example of a second ejecting member. The ejection shaft  9  is capable of receiving forward and reverse driving force from a driving source (not shown). Thus, the ejecting roller  11  is capable of rotating in forward and reverse directions. A compile sensor SN 2 , which detects sheets S on the compiler tray  1 , is disposed upstream of the ejecting roller  11  in the ejecting direction. 
     Referring to  FIG. 4 , the clamping roller  12 , which is an example of a medium clamping member, is disposed above the ejecting roller  11 . The clamping roller  12  is moveable upward and downward between an upper position shown by the solid lines in  FIG. 4 , at which the clamping roller  12  is separated from the ejecting roller  11 , and a lower position shown by the dashed lines in  FIG. 4 , at which the clamping roller  12  is near the ejecting roller  11  and is in contact with the sheets S. 
     Referring to  FIG. 5 , the second paddle wheel  13 , which is an example of a second drawing member, is disposed above the compiler tray  1  at a position shifted from the clamping roller  12  in the front-back direction. The second paddle wheel  13  is rotatably supported. The second paddle wheel  13  includes flexible sheet contact portions  13   a  that extend radially outward. The second paddle wheel  13  receives a driving force from a driving source (not shown) through, for example, a pulley and a belt (not shown), which are examples of driving-force transmission members. 
     The second paddle wheel  13  is moveable upward and downward between an upper position shown by the solid lines in  FIG. 5 , at which the second paddle wheel  13  is separated from the compiler tray  1 , and a lower position shown by the dashed lines in  FIG. 5 , at which the second paddle wheel  13  is in contact with the sheets S on the compiler tray  1 . 
     The tampers  2  and  3 , the first paddle wheel  6 , the stapler  8 , the clamping roller  12 , and the second paddle wheel  13  of the edge binding device HTS may have structures as those described in, for example, Japanese Unexamined Patent Application Publication Nos. 2003-89463, 2006-69746, and 2009-240970, and detailed description thereof is thus omitted. 
       FIG. 6  illustrates a clamping member  16  according to the first exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , a rotating shaft  14 , which extends in the front-back direction, is disposed below the ejecting roller  11 . The rotating shaft  14  supports clamping members  16 , which are examples of pressing members. Each clamping member  16  includes a cylindrical core  16   a  that is supported by the rotating shaft  14 , an arm  16   b  that extends radially outward from the core  16   a , and a contact portion  16   c  that extends obliquely rightward with respect to the arm  16   b  from the distal end of the arm  16   b . In the first exemplary embodiment, three clamping members  16  are supported by the rotating shaft  14  at the same phase with intervals therebetween in the front-back direction. The rotating shaft  14  receives forward and reverse driving force from a stepper motor  17 , which is an example of a driving source. Accordingly, the rotating shaft  14  is rotatable in forward and reverse directions by a preset angle. Thus, each clamping member  16  is movable between a retracted position shown by the solid lines in  FIG. 6  and an operating position shown by the dashed lines in  FIG. 6 . At the retracted position, the clamping member  16  is retracted into a cover U 4   a  of a body of the finisher U 4  and separated from a region through which the sheets S ejected from the compiler tray  1  are transported to and stacked on the stacker tray TH 1 . At the operating position, which is an example of a pressing position, the clamping member  16  is in contact with the upper surface of the sheets S on the stacker tray TH 1  and presses the sheets S. 
     In  FIGS. 4 and 5 , the stacker tray TH 1 , which is an example of a medium ejection portion and which obliquely extends rightward and upward, is disposed downstream of the compiler tray  1  in the sheet transporting direction. A stacking surface TH 1   a , on which the sheets S are stacked, is provided at the top of the stacker tray TH 1 . 
     A slider  18 , which is an example of a raising-lowering member, is connected to a left end portion of the stacker tray TH. The slider  18  is supported so as to be movable in the up-down direction along guide rails  19 , which are examples of guiding portions formed on the finisher U 4 . A raising-lowering belt  23  looped around rollers  21  and  22 , which are an example of a pair of upper and lower rotating members, is disposed on the left side of the slider  18 . The slider  18  is fixed to and supported by the raising-lowering belt  23 . When the raising-lowering belt  23  is rotated in the forward or reverse direction, the stacker tray TH 1  is raised or lowered in the up-down direction. 
     The stacker tray TH 1  and the mechanism for moving the stacker tray TH 1  upward and downward may have structures as those described in, for example, Japanese Unexamined Patent Application Publication Nos. 2003-89463 and 2006-69746, and detailed description thereof are thus omitted. 
     Referring to  FIGS. 4 to 6 , an upper sensor SNa, which is an example of a first upper-surface detecting member, is disposed above the guide rails  19 . The upper sensor SNa detects the stacking surface TH 1   a  of the stacker tray TH 1  or the uppermost surface of the sheets S on the stacking surface TH 1   a . The upper sensor SNa is disposed at a height at which each clamping member  16  comes into contact with the upper surface of the sheets S on the stacker tray TH 1  and presses the sheets S when the clamping member  16  is moved to the operating position. A lower sensor SNb, which is an example of a second upper-surface detecting member, is disposed below the upper sensor SNa with a preset gap therebetween. Similar to the upper sensor SNa, the lower sensor SNb detects, for example, the uppermost surface of the sheets S on the stacking surface TH 1   a  of the stacker tray TH 1 . 
     Control Section of First Exemplary Embodiment 
       FIG. 7  is a block diagram illustrating functions of a control section of the image forming apparatus according to the first exemplary embodiment. 
       FIG. 8  is a block diagram that continues from the block diagram illustrated in  FIG. 7  and illustrates functions of the control section of the image forming apparatus according to the first exemplary embodiment. 
     Referring to  FIGS. 7 and 8 , the controller C includes an input/output (I/O) interface which receives and transmits signals to and from an external unit and adjusts the input/output signal level; a read only memory (ROM) in which programs, data, etc., for executing necessary processes are stored; a random access memory (RAM) which temporarily stores necessary data; a central processing unit (CPU) that performs processes in accordance with the programs stored in the ROM; and a microcomputer that includes a clock oscillator. Various functions may be realized by executing the programs stored in the ROM. 
     Signal Input Elements Connected to Controller C 
     The controller C receives signals output from, for example, the following signal outputting elements UI. 
     UI: User Interface 
     The user interface UI includes a display panel UI 1 , a copy start key UI 2 , a copy-number input key U 13 , numeric keys UI 4 , and a process setting key UI 5  through which a process to be performed (for example, saddle stitching, corner binding, side edge binding, alignment only (no binding is performed), or direct ejection to the stacker tray TH 1 ) is set. 
     SN 1 : Exit Sensor 
     The exit sensor SN 1  detects sheets S that are transported along the edge-binding transport path SH 15  and fed to the compiler tray  1 . 
     SN 2 : Compile Sensor 
     The compile sensor SN 2  detects the sheets S on the compiler tray  1 . 
     SNa: Upper Sensor 
     The upper sensor SNa detects the stacking surface TH 1   a  of the stacker tray TH 1  or the uppermost surface of the sheets S on the stacking surface TH 1   a.    
     SNb: Lower Sensor 
     The lower sensor SNb detects the stacking surface TH 1   a  of the stacker tray TH 1  or the uppermost surface of the sheets S on the stacking surface TH 1   a.    
     Controlled Elements Connected to Controller C 
     The controller C outputs control signals to the following controlled elements. 
     D: Laser Driving Circuit 
     The laser driving circuit D drives the exposure devices ROSy to ROSk to form electrostatic latent images on the photoconductors Py to Pk. 
     D 0 : Motor Driving Circuit 
     A motor driving circuit D 0  drives a motor M 0  to rotate the photoconductors Py to Pk, developing rollers (not shown) of the developing devices Gy to Gk, the heating roller Fh, the registration roller Rr, and the transport rollers Ra by using gears (not shown). 
     E: Power Supply Circuit 
     The power supply circuit E includes the following power supply circuits. 
     E 1   y  to E 1   k : Developing Power Supply Circuits 
     Developing power supply circuits E 1   y  to E 1   k  apply developing biases to the developing rollers (not shown) of the developing devices Gy to Gk. 
     E 2   y  to E 2   k : Charging Power Supply Circuits 
     Charging power supply circuits E 2   y  to E 2   k  apply charging biases to the chargers CCy to CCk. 
     E 3   y  to E 3   k : First Transfer Power Supply Circuits 
     First transfer power supply circuits E 3   y  to E 3   k  apply first transfer biases to the first transfer rollers T 1   y  to T 1   k.    
     E 4 : Second Transfer Power Supply Circuit 
     A second transfer power supply circuit E 4  applies a second transfer bias to the contact roller T 2   c.    
     E 5 : Fixing Power Supply Circuit 
     A fixing power supply circuit E 5  supplies heating electric power to the heating roller Fh. 
     D 1 : Tamper Driving Circuit 
     A tamper driving circuit D 1  controls forward and reverse rotations of a tamper driving motor M 1  to operate the tampers  2  and  3 . 
     D 2 : Edge-Binding-Stapler Moving Circuit 
     An edge-binding-stapler moving circuit D 2  controls forward and reverse rotations of a stapler driving motor M 2  to move the stapler  8  along the stapler guide  7 . 
     D 3 : Edge-Binding-Stapler Operating Circuit 
     An edge-binding-stapler operating circuit D 3  controls a cam-driving motor M 3  to rotate an eccentric cam  8   a  so that the stapler  8  ejects a staple (not shown) to bind a stack of sheets together. 
     D 4 : Ejecting-Roller Driving Circuit 
     An ejecting-roller driving circuit D 4  controls forward and reverse rotations of an ejecting-roller driving motor M 4  to rotate the ejecting roller  11  in the forward and reverse directions. 
     D 5 : Clamping-Member Operating Circuit 
     A clamping-member operating circuit D 5  controls forward and reverse rotations of the stepper motor  17  to move each clamping member  16  between the operating position and the retracted position. 
     D 6 : Clamping-Roller Raising-Lowering Circuit 
     A clamping-roller raising-lowering circuit D 6  controls the on-off state of a clamping-roller raising-lowering solenoid SL 1  to move the clamping roller  12  between the upper position and the lower position. 
     D 7 : Second-Paddle-Wheel Raising-Lowering Circuit 
     A second-paddle-wheel raising-lowering circuit D 7  controls the on-off state of a second-paddle-wheel raising-lowering solenoid SL 2  to move the second paddle wheel  13  between the upper position and the lower position. 
     D 8 : Post-Processing Transport Driving Circuit 
     A post-processing transport driving circuit D 8  controls a post-processing transport driving motor M 5  to drive the transport rollers such as the ejection roller Rh 1  and the exit roller Rh 2 . 
     D 9 : Stacker-Tray Operating Circuit 
     A stacker-tray operating circuit D 9  controls a stacker-tray operating motor M 6  to move the stacker tray TH 1  in the up-down direction. 
     D 10 : Switching-Gate Control Circuit 
     A switching-gate control circuit D 10  controls switching-gate operating solenoids SL 3  and SL 4  to move the switching gates GT 11  and GT 12 . 
     D 11 : Saddle-Stitching-Device Control Circuit 
     A saddle-stitching-device control circuit D 11  controls a control device of, for example, the stapler of the saddle stitching device NTS to perform saddle stitching on a stack of recording sheets. 
     Functions of Controller C 
     The controller C has programs (function realizing units) based on which the controller C performs processes in accordance with the output signals from the signal outputting elements to realize the functions of outputting control signals to the controlled elements. The programs (function realizing units) for realizing the functions of the controller C will now be described. 
     C 1 : Motor Rotation Control Unit 
     A motor rotation control unit C 1  controls the motor driving circuit D 0  to control the rotations of, for example, the photoconductors Py to Pk, the developing rollers of the developing devices Gy to Gk, and the fixing device F. 
     C 2 : Power-Supply-Circuit Control Unit 
     A power-supply-circuit control unit C 2  includes units C 2   a  to C 2   e , and controls the power supply circuit E to control the developing biases, the charging biases, the transfer biases, and the on-off state of a heater of the heating roller Fh. 
     C 2   ay  to C 2   ak : Developing-Bias Control Units 
     Developing-bias control units C 2   ay  to C 2   ak  control the operations of the developing power supply circuits E 1   y  to E 1   k  to control the developing biases applied to developing rollers of the developing devices Gy to Gk. 
     C 2   by  to C 2   bk : Charging-Bias Control Units 
     Charging-bias control units C 2   by  to C 2   bk  control the operations of the charging power supply circuits E 2   y  to E 2   k  to control the charging biases applied to the chargers CCy to CCk. 
     C 2   cy  to C 2   ck : First-Transfer-Bias Control Units 
     First-transfer-bias control units C 2   cy  to C 2   ck  control the operations of the first transfer power supply circuits E 3   y  to E 3   k  to control the transfer biases applied to the first transfer rollers T 1   y  to T 1   k.    
     C 2   d : Second-Transfer-Bias Control Unit 
     A second transfer bias control unit C 2   d  controls the operation of the second transfer power supply circuit E 4  to control the transfer bias applied to the contact roller T 2   c.    
     C 2   e : Fixing-Power-Supply Control Unit 
     A fixing-power-supply control unit C 2   e  controls the operation of the fixing power supply circuit E 5  to control the on-off state of the heater of the heating roller Fh. 
     C 3 : Job Control Unit 
     A job control unit C 3  executes a job, which is an example of an image recording operation, in accordance with an input from the copy start key U 12  by controlling the operations of, for example, the exposure devices ROSy to ROSk, the photoconductors Py to Pk, the transfer rollers T 1   y  to T 1   k , T 2   c , and the fixing device F. 
     C 4 : Tamper Control Unit 
     A tamper control unit C 4  operates the tampers  2  and  3  in accordance with the size of the sheets S fed to the compiler tray  1 . More specifically, the tamper control unit C 4  operates the tampers  2  and  3  so as to align the side edges of the sheets S fed to the compiler tray  1 . The tamper control unit C 4  of the first exemplary embodiment operates the tampers  2  and  3  in a “stapling mode”, in which corner binding or side edge binding is performed, or an “aligning mode”, in which the edges of the sheets S are simply aligned. After the binding process in the “stapling mode”, or after the aligning process in the “aligning mode”, the tamper control unit C 4  causes the tampers  2  and  3  to move the sheet stack on the compiler tray  1  in the width direction to enable offset ejection, so that the sheet stack is ejected to the stacker tray TH 1  at a position shifted in the width direction from the sheet stacks on the stacker tray TH 1 . 
     C 5 : Edge-Binding-Stapler Movement Control Unit 
     An edge-binding-stapler movement control unit C 5  controls the edge-binding-stapler moving circuit D 2  in accordance with inputs from the process setting key U 15  to move the stapler  8  to a home position, an edge-binding stapling position, or a corner-binding stapling position. 
     C 6 : Edge-Binding-Stapler Operation Control Unit 
     An edge-binding-stapler operation control unit C 6  controls the edge-binding-stapler operating circuit D 3  to operate the stapler and bind a sheet stack together. The edge-binding-stapler operation control unit C 6  of the first exemplary embodiment causes the stapler  8  to staple the aligned sheet stack after the stapler  8  is moved to the desired stapling position. 
     C 7 : Ejecting-Roller Drive Control Unit 
     An ejecting-roller drive control unit C 7  controls the ejecting-roller driving circuit D 4  to rotate the ejecting roller  11  in the forward or reverse direction so that the sheets S are ejected to the stacker tray TH 1  or drawn toward the compiler tray  1 . 
     In a “direct ejection mode”, in which the sheets S are directly ejected to the stacker tray TH 1 , the ejecting-roller drive control unit C 7  of the first exemplary embodiment causes the ejecting roller  11  to rotate in the forward direction when the sheets S are transported to the compiler tray  1 . Thus, the sheets S may be clamped between the ejecting roller  11  and the clamping roller  12  and ejected. 
     In the “stapling mode” or “aligning mode”, the ejecting-roller drive control unit C 7  of the first exemplary embodiment causes the ejecting roller  11  to rotate in the reverse direction when the first one of the sheets S to be stacked together is fed to the compiler tray  1 , more specifically, after a preset time since the trailing end of the first sheet S in the transporting direction thereof has passed the exit sensor SN 1 . Thus, the sheet S may be clamped between the ejecting roller  11  and the clamping roller  12  and drawn. When the second and the following sheets S are fed to the compiler tray  1 , the ejecting-roller drive control unit C 7  stops the ejecting roller  11 . After the aligning process or the stapling process is finished and the movement of the sheets S in the width direction by the tampers  2  and  3  is also finished, the ejecting-roller drive control unit C 7  causes the ejecting roller  11  to rotate in the forward direction. Thus, the sheets S may be clamped between the ejecting roller  11  and the clamping roller  12  and ejected. 
     C 8 : Clamping-Roller Raising-Lowering Control Unit 
     A clamping-roller raising-lowering control unit C 8  controls the clamping-roller raising-lowering circuit D 6  to move the clamping roller  12  between the upper position and the lower position so that the clamping roller  12  moves toward and away from the ejecting roller  11 . The clamping-roller raising-lowering control unit C 8  of the first exemplary embodiment causes the clamping roller  12  to move to the lower position when the ejecting roller  11  rotates in the forward or reverse direction. In the “direct ejection mode”, the clamping-roller raising-lowering control unit C 8  of the first exemplary embodiment causes the clamping roller  12  to move to the lower position. Thus, the clamping roller  12  may clamp the sheets S together with the ejecting roller  11  that rotates in the forward direction, and the sheets S may be ejected to the stacker tray TH 1 . 
     In the “stapling mode” or “aligning mode”, the clamping-roller raising-lowering control unit C 8  of the first exemplary embodiment causes the clamping roller  12  to move to the lower position when the first one of the sheets S to be stacked together is fed to the compiler tray  1 , more specifically, after a preset time since the trailing end of the first sheet S in the transporting direction thereof has passed the exit sensor SN 1 . Thus, the clamping roller  12  may clamp the sheet S together with the ejecting roller  11  that rotates in the reverse direction, and the sheet S may be drawn toward the first paddle wheel  6 . When the second and the following sheets S are fed to the compiler tray  1 , the clamping-roller raising-lowering control unit C 8  of the first exemplary embodiment causes the clamping roller  12  to move to the upper position so that the clamping roller  12  is separated from the ejecting roller  11 . 
     After the aligning process or the stapling process is finished and the movement of the sheets S in the width direction by the tampers  2  and  3  is also finished, the clamping-roller raising-lowering control unit C 8  of the first exemplary embodiment causes the clamping roller  12  to move to the lower position. Thus, the clamping roller  12  may clamp the sheet stack together with the ejecting roller  11  that rotates in the forward direction, and the sheet stack may be ejected to the stacker tray TH 1 . After the ejection of the sheet stack is finished, the clamping-roller raising-lowering control unit C 8  of the first exemplary embodiment causes the clamping roller  12  to move to the upper position. 
     C 9 : Second-Paddle-Wheel Raising-Lowering Control Unit 
     A second-paddle-wheel raising-lowering control unit C 9  controls the second-paddle-wheel raising-lowering circuit D 7  to move the second paddle wheel  13  between the upper position and the lower position. In the “stapling mode” and the “aligning mode”, the second-paddle-wheel raising-lowering control unit C 9  of the first exemplary embodiment causes the second paddle wheel  13  to move between the lower position and the upper position in accordance with the times at which the sheets S are fed to the compiler tray  1 . More specifically, for each of the second and the following sheets fed to the compiler tray  1 , the second paddle wheel  13  is moved to the lower position after a preset time since the trailing end of each sheet S in the transporting direction thereof has passed the exit sensor SN 1 . Thus, the second paddle wheel  13  is brought into contact with the sheet S and applies a force that draws the sheet S toward the end wall  4 . The second-paddle-wheel raising-lowering control unit C 9  of the first exemplary embodiment causes the second paddle wheel  13  to move to the upper position after a preset time in which the sheet S is expected to come into contact with the end wall  4 . In the “direct ejection mode”, the second-paddle-wheel raising-lowering control unit C 9  of the first exemplary embodiment causes the second paddle wheel  13  to remain at the upper position. 
     C 10 : Clamping-Member Operation Control Unit 
     A clamping-member operation control unit C 10  controls the clamping-member operating circuit D 5  to move the clamping member  16  between the operating position and the retracted position. In the “direct ejection mode”, the clamping-member operation control unit C 10  of the first exemplary embodiment causes the clamping member  16  to remain at the retracted position. In the case where the “direct ejection mode” is not set, that is, in the “stapling mode” or the “aligning mode”, the clamping-member operation control unit C 10  of the first exemplary embodiment causes the clamping member  16  to move to the operating position when a sheet stack is ejected from the compiler tray  1 . Then, the clamping-member operation control unit C 10  of the first exemplary embodiment moves the clamping member  16  to the retracted position when the compile sensor SN 2  detects that the trailing end of the sheet stack in the transporting direction has passed the compile sensor SN 2 . 
     C 11 : Stacker-Tray Operation Control Unit 
     A stacker-tray operation control unit C 11 , which is an example of a medium-ejecting-portion control unit, includes an initializing unit C 11 A, a process-setting determination unit C 11 B, a non-binding raising-lowering unit C 11 C, and a binding raising-lowering unit C 11 D. The stacker-tray operation control unit C 11  controls the stacker-tray operating circuit D 9  and moves the stacker tray TH 1  upward or downward in accordance with the number of sheets S on the stacker tray TH 1 . 
     C 11 A: Initializing Unit 
     The initializing unit C 11 A performs a process of initializing the position of the stacker tray TH 1 . When the job is started, the initializing unit C 11 A of the first exemplary embodiment causes the stacker tray TH 1  to move upward until the upper sensor SNa detects, for example, the stacking surface TH 1   a . When the upper sensor SNa detects the stacking surface TH 1   a , the initializing unit C 11 A of the first exemplary embodiment causes the stacker tray TH 1  to move downward until the upper sensor SNa stops detecting the stacking surface TH 1   a . Then, when the upper sensor SNa stops detecting the stacking surface TH 1   a , the initializing unit C 11 A of the first exemplary embodiment causes the stacker tray TH 1  to stop. 
     C 11 B: Process-Setting Determination Unit 
     The process-setting determination unit C 11 B determines whether or not the sheets S are to be ejected to the stacker tray TH 1  without being subjected to the stapling process or after being subjected to the stapling process on the basis of the inputs from the process setting key UI 5 . In the first exemplary embodiment, it is determined that the sheets S are to be ejected to the stacker tray TH 1  after being subjected to the stapling process when, for example, “corner binding” or “edge binding” is set, that is, in the “stapling mode”. In addition, in the first exemplary embodiment, it is determined that the sheets S are to be ejected to the stacker tray TH 1  without being subjected to the stapling process when, for example, “alignment only” or “direct ejection” is set, that is, when the “stapling mode” is not set. 
     C 11 C: Non-Binding Raising-Lowering Unit 
     When the sheets S are ejected to the stacker tray TH 1  without being subjected to the binding process, the non-binding raising-lowering unit C 11 C, which is an example of a first raising-lowering unit, causes the stacker tray TH 1  to move to a preset first position at which the uppermost surface of the sheets S on the stacker tray TH 1  is in contact with the clamping member  16 . When it is determined that the “stapling mode” is not set, the non-binding raising-lowering unit C 11 C of the first exemplary embodiment controls the upward and downward movement of the stacker tray TH 1  on the basis of the detection result obtained by the upper sensor SNa, which is an example of a first position detecting member. 
     In the case where the “stapling mode” is not set, the non-binding raising-lowering unit C 11 C of the first exemplary embodiment determines whether or not the stacking surface TH 1   a , for example, is detected by the upper sensor SNa when the position initialization is finished. When it is determined that the stacking surface TH 1   a , for example, is detected by the upper sensor SNa, the non-binding raising-lowering unit C 11 C of the first exemplary embodiment causes the stacker tray TH 1  to move downward until the upper sensor SNa stops detecting the stacking surface TH 1   a . Then, when the upper sensor SNa stops detecting the stacking surface TH 1   a , the non-binding raising-lowering unit C 11 C of the first exemplary embodiment causes the stacker tray TH 1  to stop. This process is repeated until the job is finished. 
     C 11 D: Binding Raising-Lowering Unit 
     When the sheets S are ejected to the stacker tray TH 1  after being subjected to the binding process, the binding raising-lowering unit C 11 D, which is an example of a second raising-lowering unit, causes the stacker tray TH 1  to move to a preset second position that is below the first position and at which the uppermost surface of the sheets S on the stacker tray TH 1  is separated from the clamping member  16 . When it is determined that the “stapling mode” is set, the binding raising-lowering unit C 11 D of the first exemplary embodiment controls the upward and downward movement of the stacker tray TH 1  on the basis of the detection result obtained by the lower sensor SNb, which is an example of a second position detecting member. Thus, the binding raising-lowering unit C 11 D of the first exemplary embodiment differs from the non-binding raising-lowering unit C 11 C in that the upward and downward movement of the stacker tray TH 1  is controlled on the basis of the detection result of the lower sensor SNb instead of the upper sensor SNa. The binding raising-lowering unit C 11 D is similar to the non-binding raising-lowering unit C 11 C in other respects, and detailed description thereof is thus omitted. 
     C 12 : Post-Processing Transport Control Unit 
     A post-processing transport control unit C 12  controls the post-processing transport driving circuit D 8  to transport the sheets S in accordance with the time when the sheets S are fed to the finisher U 4 . 
     C 13 : Switching-Gate Control Unit 
     A switching-gate control unit C 13  controls the switching gates GT 11  and GT 12  to transport the sheets S fed to the feeding path SH 11  to one of the saddle-stitching transport path SH 13 , the ejection path SH 14 , and the edge-binding transport path SH 15  in accordance with the inputs from the process setting key U 15 . 
     C 14 : Saddle-Stitching-Device Control Unit 
     A saddle-stitching-device control unit C 14  controls the saddle-stitching-device control circuit D 11  so that the saddle stitching device NTS performs saddle stitching on the sheet stack when saddle stitching is set according to the inputs from the process setting key UI 5 . 
     Flowchart of First Exemplary Embodiment 
     The procedure of controlling the printer U of the first exemplary embodiment will now be described with reference to a flowchart. 
     Flowchart of Stacker-Tray Raising-Lowering Process 
       FIG. 9  is a flowchart of a stacker-tray raising-lowering process according to the first exemplary embodiment. 
     Each step ST in the flowchart of  FIG. 9  is executed in accordance with the programs stored in the controller C of the printer U. This process is executed in parallel with other processes of the printer U. 
     The flowchart of  FIG. 9  is started when the power of the printer U is turned on. 
     In ST 1  of  FIG. 9 , it is determined whether or not the job has been started. When the result of the determination is Yes (Y), the process proceeds to ST 2 . When the result of the determination is No (N), ST 1  is repeated. 
     In ST 2 , the stacker tray TH 1  starts to move upward. Then, the process proceeds to ST 3 . 
     In ST 3 , it is determined whether or not the stacking surface TH 1   a , for example, is detected by the upper sensor SNa, that is, whether or not the upper sensor SNa is ON. When the result of the determination is Yes (Y), the process proceeds to ST 4 . When the result of the determination is No (N), ST 3  is repeated. 
     In ST 4 , the stacker tray TH 1  starts to move downward. Then, the process proceeds to ST 5 . 
     In ST 5 , it is determined whether or not the stacking surface TH 1   a , for example, is undetected by the upper sensor SNa, that is, whether or not the upper sensor SNa is OFF. When the result of the determination is Yes (Y), the process proceeds to ST 6 . When the result of the determination is No (N), ST 5  is repeated. 
     In ST 6 , the stacker tray TH 1  is stopped. Then, the process proceeds to ST 7 . 
     In ST 7 , it is determined whether or not the “stapling mode” is set. When the result of the determination is Yes (Y), the process proceeds to ST 8 . When the result of the determination is No (N), the process proceeds to ST 13 . 
     In ST 8 , it is determined whether or not the stacking surface TH 1   a , for example, is detected by the lower sensor SNb, that is, whether or not the lower sensor SNb is ON. When the result of the determination is Yes (Y), the process proceeds to ST 9 . When the result of the determination is No (N), ST 8  is repeated. 
     In ST 9 , the stacker tray TH 1  starts to move downward. Then, the process proceeds to ST 10 . 
     In ST 10 , it is determined whether or not the stacking surface TH 1   a , for example, is undetected by the lower sensor SNb, that is, whether or not the lower sensor SNb is OFF. When the result of the determination is Yes (Y), the process proceeds to ST 11 . When the result of the determination is No (N), ST 10  is repeated. 
     In ST 11 , the stacker tray TH 1  is stopped. Then, the process proceeds to ST 12 . 
     In ST 12 , it is determined whether or not the job is finished. When the result of the determination is Yes (Y), the process returns to ST 1 . When the result of the determination is No (N), the process returns to ST 8 . 
     In ST 13 , it is determined whether or not the stacking surface TH 1   a , for example, is detected by the upper sensor SNa, that is, whether or not the upper sensor SNa is ON. When the result of the determination is Yes (Y), the process proceeds to ST 14 . When the result of the determination is No (N), ST 13  is repeated. 
     In ST 14 , the stacker tray TH 1  starts to move downward. Then, the process proceeds to ST 15 . 
     In ST 15 , it is determined whether or not the stacking surface TH 1   a , for example, is undetected by the upper sensor SNa, that is, whether or not the upper sensor SNa is OFF. When the result of the determination is Yes (Y), the process proceeds to ST 16 . When the result of the determination is No (N), ST 15  is repeated. 
     In ST 16 , the stacker tray TH 1  is stopped. Then, the process proceeds to ST 17 . 
     In ST 17 , it is determined whether or not the job is finished. When the result of the determination is Yes (Y), the process returns to ST 1 . When the result of the determination is No (N), the process returns to ST 13 . 
     Flowchart of Clamping-Member Controlling Process 
       FIG. 10  is a flowchart of a clamping-member controlling process according to the first exemplary embodiment. 
     Each step ST in the flowchart of  FIG. 10  is executed in accordance with the programs stored in the controller C of the printer U. This process is executed in parallel with other processes of the printer U. 
     The flowchart of  FIG. 10  is started when the power of the printer U is turned on. 
     In ST 61  of  FIG. 10 , it is determined whether or not the job has been started. When the result of the determination is Yes (Y), the process proceeds to ST 62 . When the result of the determination is No (N), ST 61  is repeated. 
     In ST 62 , it is determined whether or not the “direct ejection mode” is set. When the result of the determination is Yes (Y), the process proceeds to ST 63 . When the result of the determination is No (N), the process proceeds to ST 64 . 
     In ST 63 , it is determined whether or not the job is finished. When the result of the determination is Yes (Y), the process returns to ST 61 . When the result of the determination is No (N), ST 63  is repeated. 
     In ST 64 , it is determined whether or not the ejection of the sheets S from the compiler tray  1  has been started, that is, whether or not forward rotation of the ejecting roller  11  has been started. When the result of the determination is Yes (Y), the process proceeds to ST 65 . When the result of the determination is No (N), ST 64  is repeated. 
     In ST 65 , each clamping member  16  is moved to the operating position. Then, the process proceeds to ST 66 . 
     In ST 66 , it is determined whether or not the trailing end of the sheet stack has passed the compile sensor SN 2 , that is, whether or not the compile sensor SN 2  is OFF. When the result of the determination is Yes (Y), the process proceeds to ST 67 . When the result of the determination is No (N), ST 66  is repeated. 
     In ST 67 , each clamping member  16  is moved to the retracted position. Then, the process proceeds to ST 68 . 
     In ST 68 , it is determined whether or not the job is finished. When the result of the determination is Yes (Y), the process returns to ST 61 . When the result of the determination is No (N), the process returns to ST 64 . 
     Operation of First Exemplary Embodiment 
     In the printer U according to the first exemplary embodiment having the above-described structure, the sheets S having images recorded thereon by the printer body U 3  are fed to the finisher U 4 . The sheets S fed to the finisher U 4  are transported to one of the top tray TH 0 , the saddle stitching device NTS, and the edge binding device HTS depending on the settings input through the process setting key UI 5 . More specifically, in the first exemplary embodiment, the sheets S are transported to the top tray TH 0  in accordance with the initial settings when no input has been made through the process setting key UI 5 . When saddle stitching is set through the process setting key UI 5 , the sheets S are transported to the saddle stitching device NTS and ejected to the saddle-stitching stacker tray TH 2 . When alignment only, direct ejection to the stacker tray TH 1 , corner binding, or side edge binding is set through the process setting key UI 5 , the sheets S are transported to the edge binding device HTS and ejected to the stacker tray TH 1  that is movable upward and downward. 
     More specifically, in the finisher U 4  according to the first exemplary embodiment, when the “aligning mode”, in which the sheets S are simply aligned, is set, the sheets S transported to the edge-binding transport path SH 15  are fed to the compiler tray  1  by the exit roller Rh 2 . The ejecting roller  11  is rotated in the reverse direction after a preset time since the first one of the sheets S to be stacked together has passed the exit sensor SN 1 . Also, the clamping roller  12  is moved downward. Thus, the first sheet S fed to the compiler tray  1  is clamped between the ejecting roller  11  and the clamping roller  12  and drawn toward the first paddle wheel  6 . After that, the ejecting roller  11  is stopped and the clamping roller  12  is moved upward away from the ejecting roller  11 . The first paddle wheel  6  causes the sheet S to abut against the end wall  4 , thereby aligning the trailing edge of the sheet S in the transporting direction thereof. When the trailing edge of the sheet S in the transporting direction thereof is aligned, the tampers  2  and  3  are activated to align the edges of the sheet S in the width direction. 
     When the second and the following sheets S to be stacked together are fed to the compiler tray  1 , the second paddle wheel  13  is moved downward after a preset time since each sheet S has passed the exit sensor SN 1 . The second paddle wheel  13  draws the sheet S placed on the sheets S that have already been fed to the compiler tray  1  toward the first paddle wheel  6 . Thus, the second and the following sheets S are also caused to abut against the end wall  4  by the first paddle wheel  6 , so that the trailing edges of the sheets S in the transporting direction thereof are aligned. When the trailing edges of the sheets S in the transporting direction thereof are aligned, the tampers  2  and  3  are activated to align the edges of the sheets S in the width direction. Thus, in the edge binding device HTS of the first exemplary embodiment, all of the sheets S to be stacked together are fed to the compiler tray  1  and aligned. 
     When the alignment is finished, the tampers  2  and  3  are activated so as to move the aligned sheets S, that is, the aligned sheet stack, in the width direction so that the sheet stack is shifted from the sheet stacks that have already been ejected to the stacker tray TH 1 . Then, the clamping roller  12  is moved downward and clamps the sheet stack together with the ejecting roller  11 . Then, when the ejecting roller  11  is rotated in the forward direction, offset ejection of the sheet stack to the stacker tray TH 1  is performed. 
       FIGS. 11A to 11C  illustrate the aligning mode according to the first exemplary embodiment.  FIG. 11A  illustrates the state before the start of ejection of the sheet stack to the stacker tray TH 1 .  FIG. 11B  illustrates the state in which the ejection of the sheet stack to the stacker tray TH 1  is performed after the state of  FIG. 11A .  FIG. 11C  illustrates the state in which the sheet stack has passed the compile sensor SN 2  after the state of  FIG. 11B . 
     Referring to  FIGS. 11A to 11C , in the “aligning mode”, the upward and downward movement of the stacker tray TH 1  is controlled on the basis of the detection result of the upper sensor SNa. More specifically, the stacker tray TH 1  is controlled so that the uppermost surface of the sheets S on the stacking surface TH 1   a , for example, is at the detection position of the upper sensor SNa. 
     In the “aligning mode” according to the first exemplary embodiment, each clamping member  16  is moved to the operating position when the ejection of the sheet stack is started. Accordingly, in  FIG. 11B , the clamping member  16  is in contact with the sheets S on the stacking surface TH 1   a  and the sheets S are pressed between the clamping member  16  and the stacking surface TH 1   a . Accordingly, even when the leading end of the sheet stack ejected from the compiler tray  1  in the ejecting direction moves downward due to its own weight and the sheet stack is ejected while being in contact with the uppermost surface of the sheet stacks that have already been ejected, the uppermost sheet S is not easily dragged by the sheet stack that is being ejected. Thus, in the first exemplary embodiment, the sheets S on the stacker tray TH 1  are not easily disarranged. 
     Referring to  FIG. 11C , when the trailing end of the ejected sheet stack in the ejecting direction passes the compile sensor SN 2 , the clamping member  16  is moved to the retracted position. Accordingly, when the sheet stack ejected from the compiler tray  1  falls onto the stacker tray TH 1 , the sheet stack does not come into contact with the clamping member  16  and is not easily displaced. Therefore, the ejected sheet stack easily falls onto the stacker tray TH 1  at a preset position. As a result, in the first exemplary embodiment, the sheets S are not easily disarranged and the stacking failure of the sheets S is suppressed in the aligning mode. 
     In the finisher U 4  according to the first exemplary embodiment, in the “stapling mode”, in which edge binding or corner binding is performed, sheets S to be bound together are stacked on the compiler tray  1  and aligned as in the “aligning mode”. After the alignment, the stapler  8  moves to the edge-binding stapling position or the corner-binding stapling position in accordance with the settings, and binds the aligned sheet stack together with a staple. After the binding process, the tampers  2  and  3  and the rollers  11  and  12  are activated to perform offset ejection of the sheet stack to the stacker tray TH 1 . 
       FIGS. 12A to 12C  illustrate the stapling mode according to the first exemplary embodiment.  FIG. 12A  illustrates the state before the start of ejection of the sheet stack to the stacker tray TH′.  FIG. 12B  illustrates the state in which the ejection of the sheet stack to the stacker tray TH 1  is performed after the state of  FIG. 12A .  FIG. 12C  illustrates the state in which the sheet stack has passed the compile sensor SN 2  after the state of  FIG. 12B . 
     In the “stapling mode” according to the first exemplary embodiment, the upward and downward movement of the stacker tray TH 1  is controlled similarly to the “aligning mode” except that the movement of the stacker tray TH 1  is controlled on the basis of the detection result of the lower sensor SNb instead of the upper sensor SNa. More specifically, the stacker tray TH 1  is controlled so that the uppermost surface of the sheets S that have already been ejected, for example, is at the detection position of the lower sensor SNb. Each clamping member  16  is moved between the operating position and the retracted position similarly to the “aligning mode”. 
     Thus, referring to  FIG. 12B , in the “stapling mode” of the first exemplary embodiment, when the ejection of a sheet stack from the compiler tray  1  is started, the stacker tray TH 1  is located at a position lower than that in the “aligning mode” on the basis of the detection result of the lower sensor SNb. The clamping member  16  moves to the same operating position as that in the “aligning mode”. Accordingly, since the stacker tray TH 1  is at the lower position, the clamping member  16  at the operating position is farther from the sheets S on the stacking surface TH 1   a  than in the “aligning mode”, but is close to the sheets S. 
     In general, the clamping member presses the uppermost surface of the sheets S with a force strong enough to prevent the sheets S from being dragged when they are pulled. In recent years, there has been a demand for image forming apparatuses capable of processing a greater number of sheets in unit time, that is, image forming apparatuses with higher productivity. Accordingly, components, such as the clamping member, are generally required to move at a higher speed. Therefore, when the clamping member comes into contact with the sheets S, a large impact tends to occur and impact noise is easily generated. 
     Japanese Unexamined Patent Application Publication No. 2012-184114 describes a technology for transporting a sheet stack subjected to a stapling process by clamping a trailing end of the sheet stack in the ejecting direction. Japanese Unexamined Patent Application Publication No. 2001-322762 describes a technology for controlling upward and downward movement of a stacker tray on the basis of a detection position of a single sensor. Japanese Unexamined Patent Application Publication Nos. 2012-184114 and 2001-322762 do not describe a technology of separating a clamping member from a sheet stack subjected to a binding process. Therefore, according to the technologies described in Japanese Unexamined Patent Application Publication Nos. 2012-184114 and 2001-322762, the clamping member comes into contact with the sheet stack subjected to a binding process. This means that, according to the technologies described in Japanese Unexamined Patent Application Publication Nos. 2012-184114 and 2001-322762, there is a risk that noise is easily generated. 
     In contrast, in the “stapling mode” of the first exemplary embodiment, the clamping member  16  may be easily disposed so as to be separated from the sheets S on the stacking surface TH 1   a  when the clamping member  16  is moved to the operating position. Therefore, in the “stapling mode”, unlike the case in which the clamping member  16  comes into contact with and presses the sheet stacks, the clamping member  16  does not easily hit the sheets S and the noise is suppressed. 
     In this case, when a sheet stack is ejected from the compiler tray  1 , the sheet stacks that have already been ejected to the stacker tray TH 1  are not pressed by the clamping member  16 . However, in the “stapling mode”, the sheet stacks ejected to and placed on the stacker tray TH 1  are subjected to the binding process. The sheet stacks subjected to the binding process are heavier than individual sheets S, and are not easily dragged even when the uppermost sheet S is pulled. Therefore, in the “stapling mode”, the sheet stacks are not easily disarranged even when the clamping member  16  is separated from the sheet stacks. Accordingly, in the first exemplary embodiment, the sheets S ejected to the stacker tray TH 1  are not easily disarranged, and the noise is reduced from that in the case where the sheet stacks ejected to the stacker tray TH 1  after being subjected to the binding process are pressed by the clamping member  16 . 
     In the “stapling mode” of the first exemplary embodiment, the clamping member  16  is moved to the operating position. When the noise is to be further reduced, the clamping member  16  may be retained at the retracted position instead of being driven. However, when a sheet stack is ejected to the stacker tray TH 1 , the sheet stack may be placed such that the trailing end thereof in the ejecting direction leans against a portion of the cover U 4   a  of the finisher U 4  that is disposed below the ejecting roller  11 . When the ejection of sheet stacks is continuously performed without correcting the position of the leaning sheet stack, there is a risk that the stacker tray TH 1  will be excessively moved downward or a sheet stack will be placed on the leaning sheet stack. Thus, the stacking performance may be degraded. 
     In contrast, in the “stapling mode” according to the first exemplary embodiment, the clamping member  16  is moved to the operating position. Therefore, when there is a sheet stack that leans against the cover U 4   a , the clamping member  16  easily comes into contact with the trailing end of the leaning sheet stack in the ejecting direction, and the trailing end of the leaning sheet stack in the ejecting direction is easily removed from the cover U 4   a . Thus, the position of the leaning sheet stack is easily corrected. Accordingly, in the first exemplary embodiment, the risk that the stacking failure of the sheet stacks will occur is lower than that in the case where the clamping member  16  is retained at the retracted position. As described above, in the “stapling mode” of the first exemplary embodiment, when the ejected sheet stacks are not arranged in an orderly manner in the stacking direction, for example, when there is a sheet stack that leans against the cover U 4   a , the clamping member  16  comes into contact with the sheet stacks when the clamping member  16  is moved to the operating position. When the ejected sheet stacks are arranged in an orderly manner, the clamping member  16  does not come into contact with the sheet stacks. 
     In the printer U of the first exemplary embodiment, in the “direct ejection mode”, when a sheet S transported along the edge-binding transport path SH 15  is fed to the compiler tray  1  by the exit roller Rh 2 , the sheet S is clamped between the ejecting roller  11 , which is rotated in the forward direction, and the clamping roller  12 , which is moved downward, and is directly ejected to the stacker tray TH 1 . At this time, similarly to the “aligning mode”, the upward and downward movement of the stacker tray TH 1  is controlled on the basis of the detection result obtained by the upper sensor SNa. The clamping member  16  is not driven and retained at the retracted position. In the “direct ejection mode”, the sheets S are ejected one at a time. The ejected sheet S is lighter than the sheet stacks, and is easily ejected to a position far from the compiler tray  1  due to the momentum of the sheet S ejected from the rollers  11  and  12 . Therefore, the trailing end of the sheet S in the ejecting direction tends to fall to a position separated from the cover U 4   a , and does not easily lean against the cover U 4   a . For this reason, in the “direct ejection mode” of the first exemplary embodiment, the clamping member  16  is not driven so that the noise is reduced. 
     Second Exemplary Embodiment 
     A second exemplary embodiment of the present invention will now be described. In the second exemplary embodiment, components corresponding to those in the first exemplary embodiment are denoted by the same reference numerals, and detailed description thereof is thus omitted. 
     This exemplary embodiment differs from the first exemplary embodiment in the points described below, but is similar to the first exemplary embodiment in other points. 
       FIG. 13  illustrates a clamping member  16  according to the second exemplary embodiment of the present invention, and corresponds to  FIG. 6  illustrating the first exemplary embodiment. 
     Referring to  FIG. 13 , in the second exemplary embodiment, the number of positions to which the clamping member  16  is movable is greater than that in the first exemplary embodiment. More specifically, the clamping member  16  of the second exemplary embodiment is movable to an operating position, which is similar to that in the first exemplary embodiment and shown by the solid lines in  FIG. 13 , a retracted position, which similar to that in the first exemplary embodiment and shown by the dashed lines in  FIG. 13 , and a removing position, which is shown by one-dot chain line in  FIG. 13  and located between the operating position and the retracted position. The removing position, which is an example of a close position, is set to a position where the clamping member  16  is separated from the sheets S on the stacker tray TH 1  but is close to the sheets S on the stacker tray TH 1 . 
     In the second exemplary embodiment, the lower sensor SNb of the first exemplary embodiment is omitted. Accordingly, in the second exemplary embodiment, the stacker tray TH 1  is moved upward and downward in accordance with the detection result obtained by the upper sensor SNa. 
     Control Section of Second Exemplary Embodiment 
       FIG. 14  is a block diagram illustrating functions of a control section of an image forming apparatus according to the second exemplary embodiment. 
       FIG. 15  is a block diagram that continues from the block diagram illustrated in  FIG. 14  and illustrates functions of the control section of the image forming apparatus according to the second exemplary embodiment. Signal Input Elements Connected to Controller C′ 
     Referring to  FIGS. 14 and 15 , the second exemplary embodiment differs from the first exemplary embodiment in that the lower sensor SNb is omitted. 
     Functions of Controller C′ 
     A controller C′ of the second exemplary embodiment includes a clamping-member operation control unit C 10 ′ and a stacker-tray operation control unit C 11 ′ of the second exemplary embodiment in place of the clamping-member operation control unit C 10  and the stacker-tray operation control unit C 11  of the first exemplary embodiment. 
     C 10 ′: Clamping-Member Operation Control Unit 
     The clamping-member operation control unit C 10 ′ of the second exemplary embodiment controls the clamping-member operating circuit D 5  to move the clamping member  16  between the operating position, the retracted position, and the removing position. The second exemplary embodiment differs from the first exemplary embodiment in that the clamping-member operation control unit C 10 ′ moves the clamping member  16  to the removing position in the “stapling mode”. In the first exemplary embodiment, the clamping member  16  is moved between the operating position and the retracted position in the “stapling mode”. In contrast, in the second exemplary embodiment, the clamping member  16  is moved between the removing position and the retracted position in the “stapling mode”. In the “direct ejection mode” and the “aligning mode”, the clamping-member operation control unit C 10 ′ performs control operations similar to those in the first exemplary embodiment. Therefore, the description of the control operations performed in the “direct ejection mode” and the “aligning mode” is omitted. 
     C 11 ′: Stacker-Tray Operation Control Unit 
     The stacker-tray operation control unit C 11 ′ of the second exemplary embodiment differs from the stacker-tray operation control unit C 11  of the first exemplary embodiment in that the stacker-tray operation control unit C 11 ′ includes a raising-lowering unit C 11 C′ in place of the non-binding raising-lowering unit C 11 C and the binding raising-lowering unit C 11 D of the first exemplary embodiment. 
     C 11 C′: Raising-Lowering Unit 
     The raising-lowering unit C 11 C′, which is an example of a third raising-lowering unit, of the second exemplary embodiment controls the upward and downward movement of the stacker tray TH 1  on the basis of the detection result obtained by the upper sensor SNa irrespective of whether or not the “stapling mode” is set. The non-binding raising-lowering unit C 11 C and the binding raising-lowering unit C 11 D according to the first exemplary embodiment control the upward and downward movement of the stacker tray TH 1  on the basis of the detection result obtained by the lower sensor SNb in the “stapling mode”. In contrast, the raising-lowering unit C 11 C′ of the second exemplary embodiment controls the upward and downward movement of the stacker tray TH 1  on the basis of the detection result obtained by the upper sensor SNa not only in the “direct ejection mode” and the “aligning mode” but also in the “stapling mode”. 
     Flowchart of Second Exemplary Embodiment 
     The procedure of controlling the printer U of the second exemplary embodiment will now be described with reference to a flowchart. 
     Flowchart of Stacker-Tray Raising-Lowering Process 
       FIG. 16  is a flowchart of a stacker-tray raising-lowering process according to the second exemplary embodiment, and corresponds to  FIG. 9  illustrating the first exemplary embodiment. 
     Referring to  FIG. 16 , in the stacker-tray raising-lowering process of the second exemplary embodiment, ST 6 ′ is executed instead of ST 6  to ST 12  in the stacker-tray raising-lowering process of the first exemplary embodiment. In the second exemplary embodiment, ST 6 ′ differs from ST 6  in the first exemplary embodiment in that the process proceeds to ST 13 . In the stacker-tray raising-lowering process of the second exemplary embodiment, ST 7  to ST 12  of the first exemplary embodiment are not executed, and the process proceeds to ST 13  from ST 6 ′. The stacker-tray raising-lowering process of the second exemplary embodiment is similar to the stacker-tray raising-lowering process according to the first exemplary embodiment in other respects. 
     Flowchart of Clamping-Member Controlling Process 
       FIG. 17  is a flowchart of a clamping-member controlling process according to the second exemplary embodiment, and corresponds to  FIG. 10  illustrating the first exemplary embodiment. 
     Referring to  FIG. 17 , in the clamping-member controlling process according to the second exemplary embodiment, ST 62 ′ is executed instead of ST 62  in the clamping-member controlling process of the first exemplary embodiment. In the clamping-member controlling process of the second exemplary embodiment, ST 71 , which is executed when the result of the determination in ST 62 ′ is No (N), is additionally provided between ST 62 ′ and ST 64 . Moreover, in the clamping-member controlling process of the second embodiment, ST 72  to ST 76 , which are executed when the result of the determination in ST 71  is No (N), are additionally provided. The clamping-member controlling process of the second exemplary embodiment is similar to that of the first exemplary embodiment except for ST 62 ′, ST 71 , and ST 72  to ST 76 . Therefore, only ST 62 ′, ST 71 , and ST 72  to ST 76  will be described. 
     Referring to  FIG. 17 , in ST 62 ′, it is determined whether or not the “direct ejection mode” is set. When the result of the determination is Yes (Y), the process proceeds to ST 63 . When the result of the determination is No (N), the process proceeds to ST 71 . 
     In ST 71 , it is determined whether or not the “aligning mode” is set. When the result of the determination is Yes (Y), the process proceeds to ST 64 . When the result of the determination is No (N), the process proceeds to ST 72 . 
     In ST 72 , it is determined whether or not the ejection of the sheets S from the compiler tray  1  has been started, that is, whether or not forward rotation of the ejecting roller  11  has been started. When the result of the determination is Yes (Y), the process proceeds to ST 73 . When the result of the determination is No (N), ST 72  is repeated. 
     In ST 73 , the clamping member  16  is moved to the removing position. Then, the process proceeds to ST 74 . 
     In ST 74 , it is determined whether or not the trailing end of the sheet stack has passed the compile sensor SN 2 , that is, whether or not the compile sensor SN 2  is OFF. When the result of the determination is Yes (Y), the process proceeds to ST 75 . When the result of the determination is No (N), ST 74  is repeated. 
     In ST 75 , the clamping member  16  is moved to the retracted position. Then, the process proceeds to ST 76 . 
     In ST 76 , it is determined whether or not the job is finished. When the result of the determination is Yes (Y), the process returns to ST 61 . When the result of the determination is No (N), the process returns to ST 72 . 
     Operation of Second Exemplary Embodiment 
     In the finisher U 4 ′ according to the second exemplary embodiment having the above-described structure, the stacker tray TH 1  and the clamping member  16  are controlled similarly to the first exemplary embodiment in the “direct ejection mode” and the “aligning mode”. Accordingly, also in the second exemplary embodiment, when a sheet stack is ejected in the “aligning mode”, the clamping member  16  presses the sheet stacks on the stacker tray TH 1  and prevents the sheets S from being disarranged. 
     In the “stapling mode” according to the second exemplary embodiment, unlike the first exemplary embodiment, the upward and downward movement of the stacker tray TH 1  is controlled on the basis of the upper sensor SNa. In addition, when a sheet stack is ejected, the clamping member  16  is moved to the removing position instead of the operating position. Accordingly, when the sheet stack is ejected, the clamping member  16  is easily disposed so as to be separated from the sheets S on the stacking surface TH 1   a  of the stacker tray TH 1 . Therefore, similar to the first exemplary embodiment, also in the second exemplary embodiment, the sheets S ejected to the stacker tray TH 1  are not easily disarranged and the noise is reduced. 
     In the first exemplary embodiment, the relative distance between the clamping member  16  and the stacker tray TH 1  is changed between the “stapling mode” and the “aligning mode” by changing the way in which the upward and downward movement of the stacker tray TH 1  is controlled. In the second exemplary embodiment, the upward and downward movement of the stacker tray TH 1  is controlled in the same way, and the distance is changed by changing the way in which the rotation of the clamping member  16  is controlled. Accordingly, sufficient stacking performance of the sheet stacks ejected to the stacker tray TH 1  is ensured and the noise is reduced. 
     Also in the “stapling mode” of the second exemplary embodiment, when there is a sheet stack that leans against the cover, the clamping member  16  moved to the removing position easily comes into contact with the trailing end of the leaning sheet stack in the ejecting direction, and the position of the leaning sheet stack is easily corrected. 
     Modifications 
     Although exemplary embodiments of the present invention have been described in detail, the present invention is not limited to the exemplary embodiments, and various modifications are possible within the scope of the present invention described in the claims. Exemplary modifications (H01) to (H09) of the present invention will be described. 
     (H01) In the exemplary embodiment, the printer U is described as an example of an image forming apparatus. However, the image forming apparatus is not limited to this, and may instead be another type of machine including a post-processing device, such as a copying machine, a facsimile machine, or a multifunction machine having the functions of these machines. 
     (H02) In the above-described exemplary embodiments, the relative distance between the clamping member  16  and the stacker tray TH 1  is changed between the “stapling mode” and the “aligning mode” by changing the way in which the upward and downward movement of the stacker tray TH 1  is controlled in the first exemplary embodiment and by changing the way in which the rotation of the clamping member  16  is controlled in the second exemplary embodiment. However, the present invention is not limited to this. For example, the relative distance between the clamping member  16  and the stacker tray TH 1  may be changed between the “stapling mode” and the “aligning mode” by controlling both the stacker tray TH 1  and the clamping member  16  in each mode. 
     (H03) In each exemplary embodiment, the clamping member  16  is supported by the rotating shaft  14 , and the position thereof is controlled by applying a driving force of the stepper motor  17  to the clamping member  16 . However, the present invention is not limited to this. For example, a transmission system may be provided between the ejection shaft  9  of the ejecting roller  11  and the rotating shaft  14 , and the position of the clamping member  16  may be controlled by transmitting a driving force of the forward and reverse rotation of the ejection shaft  9  through a driving-force-transmission switching member, such as an electromagnetic clutch, for a preset time. 
     (H04) In each exemplary embodiment, the clamping member  16 , which is an example of a pressing member, is reciprocated by driving the stepper motor  17  in the forward and reverse directions. However, the movement of the pressing member is not limited to the reciprocating movement. For example, the pressing member may be configured so as to be rotatable in one direction and rotated from the pressing position or the close position to the retracted position by receiving a one-way driving force of a driving source. More specifically, a structure in which a set clamp paddle, such as those described in, for example, Japanese Unexamined Patent Application Publication Nos. 2006-69746 and 2006-69749, is moved may be applied. 
     (H05) In each exemplary embodiment, the clamping member  16  is moved by a rotational driving force applied by the stepper motor  17 . However, the driving source of the clamping member  16  is not limited to the motor. For example, the clamping member may be moved by a solenoid, which is an example of a driving source, and a spring, which is an example of an urging member. In this case, for example, a stopper that regulates the movement of the clamping member may be provided, and the position to which the clamping member is moved may be changed between the pressing position and the close position depending on the mode by changing the position of the stopper depending on the mode. 
     (H06) In each exemplary embodiment, in both the “stapling mode” and the “aligning mode”, the clamping member  16  is moved from the retracted position when the ejection of the sheet stack is started, and returned to the retracted position after the sheet stack has passed the compile sensor SN 2 . However, the present invention is not limited to this, and the clamping member  16  may be moved at a different timing. For example, in the “stapling mode”, the clamping member  16  may be moved from the retracted position when the sheet stack is ejected to the stacker tray TH 1 . 
     (H07) In each exemplary embodiment, the clamping member  16  is not driven in the “direct ejection mode”. However, the present invention is not limited to this. For example, the clamping member  16  may be driven similarly to the “aligning mode”. 
     (H08) In each exemplary embodiment, the “direct ejection mode” may be set. In the “direct ejection mode”, the sheets S fed to the compiler tray  1  are directly ejected to the stacker tray TH 1  without being stacked together. However, the “direct ejection mode” may be omitted. In other words, the structure may be such that only the sheets S to be stacked together are fed to the compiler tray  1 , and the sheets S that are not to be stacked together are ejected to the top tray TH 0 . 
     (H09) In each exemplary embodiment, when a sheet stack is ejected, the tampers  2  and  3  may be activated to perform offset ejection in which the sheet stack is shifted in the width direction. However, the present invention is not limited to this. The sheet stack may be ejected without activating the tampers  2  and  3  and shifting the sheet stack in the width direction. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.