Patent Publication Number: US-11383951-B2

Title: Sheet processing apparatus, and image forming system

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sheet processing apparatus for performing binding processing for sheets, and an image forming system. 
     Description of the Related Art 
     Conventionally, in an image forming apparatus such as a copying machine, a laser beam printer, a facsimile, or a multifunctional peripheral, there is provided a sheet processing apparatus including a binding unit that conveys and places sheets, on each of which an image has been formed, onto a processing tray and performs binding processing for the placed sheet bundle. 
     As the apparatus, there is known an apparatus that performs binding by pressure-bonding sheets without using any metal staple as a binding member from the viewpoint of power consumption and environmental protection. In this so-called pressure-bonding binding, a load is applied to a pair of groups of concave and convex pressurizing teeth, which mesh with each other, with respect to overlapping sheets to tangle fibers of the sheets, thereby performing binding. 
     In this pressure-bonding binding, sheets are bound without using any staple. For a few sheets, pressure bonding is possible. However, if the number of sheets increases, the concave and convex pressurizing teeth (pressuring teeth and receiving teeth) are difficult to mesh with each other, thereby weakening a binding force. 
     To increase the binding force, Japanese Patent No. 3481300 describes a technique of performing pressure bonding by an upper metal mold (upper pressurizing teeth) in which a triangular three-dimensional structure is formed and a lower metal mold (lower pressurizing teeth) that meshes with the upper metal mold after applying a mass of water to the surface of a sheet bundle. 
     Japanese Patent No. 3502204 describes a technique of adding water before pressure-bonding the sheets of paper in order to make it easy to tangle fibers of the sheets. In addition, Japanese Patent No. 3502204 describes a technique of supplying water along the edge of a sheet during conveyance of the sheet. 
     Japanese Patent Laid-Open No. 2014-201432 describes the use of an inkjet head that discharges water from a nozzle hole as a water addition mechanism of adding water to a binding region of a sheet to perform pressure-bonding binding. In addition, Japanese Patent Laid-Open No. 2014-201432 describes that a pressure-bonding strength is changed by changing an amount of added water. 
     Japanese Patent Laid-Open No. 2018-199553 describes a technique in which when a few sheets (two to six sheets) are placed, a normal pressure-boding operation is performed without adding water and when the number of sheets exceeds the above number, pressure boding is performed after adding water. 
     However, any of these literatures does not mention an arrangement of shortening, by shortening the time taken for a liquid to penetrate into a sheet, the time from when the liquid is applied to the sheet until pressure bonding is performed. 
     SUMMARY OF THE INVENTION 
     The present invention in one aspect provides a sheet processing apparatus for performing binding processing for a sheet bundle formed from a plurality of sheets, comprising: an application unit configured to apply a liquid to a sheet wherein the application unit applies the liquid to an outermost sheet of the sheet bundle, and a static surface tension of the liquid is lower than a static surface tension of water; and a binding processing unit configured to bind the sheet bundle, without using a staple, wherein the binding processing unit includes a pair of groups of pressurizing teeth, and the pressurizing teeth clamp and pressurize the sheet bundle, wherein in the sheet bundle, a liquid application region which is applied with the liquid and a pressurizing region which is pressurized by the pressurizing teeth are provided to overlap each other. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing the periphery of a processing tray and a binding unit; 
         FIGS. 2A and 2B  are views for explaining the arrangement of the binding unit; 
         FIGS. 3A and 3B  are views for explaining the arrangement of the binding unit; 
         FIGS. 4A and 4B  are views for explaining the arrangement of the binding unit; 
         FIGS. 5A and 5B  are views for explaining the arrangement of the binding unit; 
         FIGS. 6A and 6B  are views for explaining the arrangement of the binding unit; 
         FIGS. 7A and 7B  are views for explaining the arrangement of the binding unit; 
         FIG. 8  is a view for explaining the arrangement of a liquid replenishing pump unit; 
         FIG. 9  is a view for explaining the arrangement of the liquid replenishing pump unit; 
         FIG. 10  is a view for explaining the arrangement of the liquid replenishing pump unit; 
         FIGS. 11A, 11B, and 11C  are views for explaining an operation of performing pressure bonding by applying a liquid; 
         FIGS. 12A, 12B, and 12C  are views for explaining the operation of performing pressure bonding by applying the liquid; 
         FIGS. 13A, 13B, and 13C  are views for explaining the operation of performing pressure bonding by applying the liquid; 
         FIGS. 14A, 14B, and 14C  are views for explaining the meshing state between pressurizing teeth and receiving teeth; 
         FIG. 15  is a view for explaining the meshing state between the pressurizing teeth and the receiving teeth; 
         FIG. 16  is a view for explaining a sheet position; 
         FIGS. 17A, 17B, and 17C  are views for explaining the sheet position; 
         FIGS. 18A, 18B, 18C, and 18D  are views for explaining the relationship between the number of sheets and application of the liquid; and 
         FIG. 19  is a block diagram showing the block arrangement of a control system. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An embodiment will be described in detail below with reference to the accompanying drawings. It should be noted that the following embodiment is not intended to limit the scope of the appended claims. A plurality of features are described in the embodiment. Not all the plurality of features are necessarily essential to the present invention, and the plurality of features may arbitrarily be combined. In addition, the same reference numerals denote the same or similar parts throughout the accompanying drawings, and a repetitive description will be omitted. 
     As the embodiment of the present invention, a sheet processing apparatus (finisher) incorporated in an image forming main body apparatus will be described. However, various modifications can be made without departing from the scope of the present invention, and all the technical matters included in the technical concept described in the appended claims are the subject matters of the present invention. Note that the image forming main body apparatus is not limited, and a printing mechanism such as an electrostatic mechanism, an offset printing mechanism, an inkjet printing mechanism, or an ink ribbon transfer printing mechanism (thermal transfer ribbon printing, sublimation ribbon printing, or the like) can be adopted. 
     In this embodiment, a sheet (print medium) indicates a thin material whose fibers are loosened when water penetrates. The structure and mechanism of an apparatus for performing water-addition pressure-bonding binding according to this embodiment will be described in detail later. First, a liquid with permeability higher than that of water, to be used for binding, as the feature of this embodiment will be described in detail. 
     As a binding method according to this embodiment, fibers forming sheets are loosened and tangled. To efficiently loosen fibers, it is necessary to make water penetrate quickly into sheets to be bound. To achieve this, this embodiment has a feature that a liquid is an aqueous solution with a surface tension lower than that of water. 
     The surface tension of a liquid serves as an index of permeability into a sheet. A liquid with a low surface tension penetrates into a sheet more easily than a liquid with a high surface tension. 
     As a method of adjusting the surface tension of the liquid, there are known a method using a surfactant and a method using a solvent. If the surface tension is adjusted using a surfactant, the surface tension can be adjusted by adding a small amount of the surfactant. On the other hand, if the surface tension is adjusted using a solvent, it is necessary to add an amount of the solvent larger than that of the surfactant. Furthermore, since the solvent has high moisture retention, it prevents evaporation of water after sheets are bound. Therefore, it takes time to dry the bound sheets. For the above reasons, in this embodiment, it is preferable to adjust the surface tension of the liquid using the surfactant. In general, the surface tension is a value measured by the Wilhelmy method as a static surface tension. The value of the static surface tension of water is “72.8 mN/m”, and a liquid with a static surface tension of a lower value is used in this embodiment. More preferably, a liquid with a surface tension of “45.0 mN/m” or less is used. The static surface tension indicates a surface tension when equilibrium is reached at the interface of a liquid and a gas by the lapse of time. 
     Furthermore, in this embodiment, the value of the dynamic surface tension of the liquid is preferably low. The dynamic surface tension serves as an index different from the above-described static surface tension. 
     The static surface tension corresponds to the value of the surface tension when equilibrium is reached after a material exhibiting the surface active property is fully oriented on the interface between the liquid and the gas. On the other hand, the dynamic surface tension indicates the surface tension measured within the time until the material exhibiting the surface active property is fully oriented. That is, the dynamic surface tension serves as an index for a temporal change of the surface tension. Alternatively, the dynamic surface tension can be said as the value of the surface tension after a predetermined time since generation of a gas-liquid interface. The dynamic surface tension can be measured by the maximum bubble pressure method, the drop volume method, or the like. 
     In this embodiment, it is desirable that a liquid quickly penetrates into a sheet in order to shorten the time taken to perform binding. Therefore, a liquid whose surface tension becomes low in a short time is suitable for this embodiment. Although the measurement time of the dynamic surface tension is not particularly limited, a result of performing measurement within 100 msec after generation of the gas-liquid interface is preferably lower, and a result of performing measurement within 50 msec is more preferably lower. That is, the liquid used in this embodiment is preferably a liquid whose surface tension changes to a value close to the static surface tension in a short time. 
     The value of the surface tension of water after 100 msec is “72.5 mN/m”, and the value of the surface tension after 50 msec is “72.3 mN/m”. The liquid used in this embodiment preferably has a surface tension lower than these values. As described above, the liquid is preferably a liquid whose surface tension changes to a value close to the static surface tension in a short time. 
     Furthermore, in this embodiment, the surface tension of the liquid is preferably equal to or lower than the critical surface tension of the sheets to be bound. The critical surface tension indicates a surface tension when the contact angle of the liquid contacting a solid is 0°. If the surface tension of the liquid is equal to or lower than the critical surface tension of the contacting solid, a tendency that the liquid actively spreads with respect to the solid is indicated. Therefore, the liquid readily penetrates into the sheet. 
     The critical surface tension will be described. As a method of measuring the critical surface tension of a target solid, there is provided a general method proposed by Zisman. For each of a plurality of saturated hydrocarbon liquids with different surface tensions (γ), a contact angle θ with the target is measured. Then, the relationship between the surface tension (γ) and the cosine (COS θ) of the contact angle is plotted. Based on the result of plotting, the value of the surface tension (γ) extrapolated so that the value of the cosine (COS θ) of the contact angle becomes 1 indicates the critical surface tension of the target. 
     However, in this embodiment, since a print medium focusing on plain paper (a general printing sheet) as a target which the liquid is made to contact has a critical surface tension of a high value, the above-described measurement method using the saturated hydrocarbon liquids may not implement correct measurement. In this embodiment, therefore, the critical surface tension is measured using solutions obtained by mixing water and ethanol at a plurality of mixing ratios. 
     As a result of the measurement, the critical surface tension of the plain paper has a value of “45 mN/m”. The surface tension of the liquid used in this embodiment preferably has a value equal or lower than this value. Note that if there are a plurality of types of sheets to be bound, the surface tension of the liquid is preferably made to be equal to or lower than the lowest value of the critical surface tension. 
     An organic solvent for adjusting the surface tension to be preferably used in this embodiment is not particularly limited as long as it can be dissolved in water. Examples of the organic solvent are polyhydric alcohols such as 1,3-butyl glycol, 3-methyl-1,3-butyl glycol, triethylene glycol, polyethylene glycol, 1,5-pentanediol, 1,6-hexanediol, 1,2-hexanediol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, and 3-methyl-1,3,5-pentanetriol, polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether, polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether, nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl imidazolidinone, ε-Caprolactam, and γ-Butyrolactone, amides such as formamide, N-methyl formamide, and N,N-dimethylformamide, amines such as monoethanolamine, diethanolamine, and triethylamine, sulphur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol, propylene carbonate, and ethylene carbonate. Each of these water-soluble organic solvents can be used singly, or two or more of them can be mixed and used. To achieve a predetermined surface tension, an amount of a solvent to be added is preferably smaller. 
     The surfactant for adjusting the surface tension, which is preferably used in this embodiment, is not particularly limited. Examples of the surfactant are as follows. Note that a single surfactant or a plurality of surfactants may be used. 
     [Nonionic Surfactant] polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene alkyl phenyl ether, a polyoxyethylene/polyoxypropylene block polymer, fatty acid diethanolamide, an acetylene glycol ethylene oxide adduct, an acetylene glycol-based surfactant, and the like. 
     [Anionic Surfactant] polyoxyalkylene alkyl ether sulfuric acid ester salt, polyoxyalkylene alkyl ether sulfonic acid salt, polyoxyalkylene alkyl phenyl ether sulfuric acid ester salt, polyoxyalkylene alkyl phenyl ether sulfonic acid salt, alpha-sulfofatty acid ester salt, alkyl benzene sulfonic acid salt, alkyl phenol sulfonic acid salt, alkyl naphthalene sulfonic acid salt, alkyltetralin sulfonic acid salt, dialkylsulfosuccinic acid salt, and the like. 
     [Cationic Surfactant] alkyltrimethylammonium salt, dialkyldimethylammonium chloride, and the like. 
     [Amphoteric Surfactant] alkylcarboxybetaine and the like. 
     Among them, an acetylene glycol-based surfactant, polyoxyethylene alkyl ether, and the like can improve the ink discharge stability, and are thus particularly, preferably used. As the acetylene glycol-based surfactant, (an ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol) is preferable. 
     The sheet used in the sheet processing apparatus according to this embodiment is not particularly limited, and may be any paper generally used for printing. As an example, so-called plain paper or PPC paper with a basis weight of 100 g/cm 2  or less is preferably used. More preferably, any sheet with a basis weight of 90 g/cm 2  or less can preferably be used. If the basis weight is larger, the sheet is thick, and it is thus difficult to obtain the effect of this embodiment. 
     The structure and mechanism of a binding unit, which binds sheets using the liquid, of the sheet processing apparatus using this embodiment will be described. Note that in the sheet processing apparatus according to this embodiment, an arrangement capable of coping with both a case in which the liquid is used in accordance with the number of sheets to be bound and a case in which sheets are bound without using the liquid according to this embodiment will be explained. This embodiment is applied to binding when the liquid is used, as a matter of course. 
       FIG. 1  is a view showing the arrangement of the periphery of the binding unit that binds sheets by the finisher. As shown in  FIG. 1 , alignment plates  59  that move a sheet in a width direction intersecting a sheet conveyance direction every time the sheet is conveyed from a conveyance roller (not shown) are provided on a processing tray  58  on which the sheet is placed. The alignment plates  59  are provided to be moved by an alignment plate motor  59 M shown in  FIG. 19  to sandwich the sheet by the two sides in the sheet width direction. This moves the alignment plates  59  in a direction of narrowing the spacing between them, thereby performing alignment in the sheet width direction. On the processing tray  58 , a discharge port (not shown) and reference stoppers  62  which are inclined downward and used to make a sheet switch-back conveyed by a return paddle or the like abut against their end portions are arranged. 
     A binding unit  60  as a binding processing unit shown in  FIG. 1  adopts a pressure-boding binding of binding sheets by performing pressure bonding by pressuring teeth without using any metal staple, and can also perform so-called water-addition pressure-bonding binding of binding sheets by adding a liquid to the sheet at the time of pressure bonding. Note that application of a liquid containing water may be expressed as “water addition” for the sake of descriptive convenience hereinafter. At the time of manual binding or water supply, the binding unit  60  is located at an HP position (home position) shown in  FIG. 1 . Furthermore, at the time of front binding, rear binding, or 2-point binding, the binding unit  60  is moved to each corresponding position. 
     [Arrangement for Water-Addition Pressure-Bonding Binding] 
     The binding unit  60  that applies the liquid to the binding position of the sheet and then performs pressure bonding will be described with reference  FIG. 2A  and subsequent drawings.  FIGS. 2A and 2B  are perspective views of the (water-addition pressure-bonding) binding unit  60 .  FIG. 2A  shows the rear side and  FIG. 2B  shows the front side.  FIGS. 3A and 3B  are side views of the binding unit  60 .  FIG. 3A  is a view when viewed from the rear side of the sheet processing apparatus and  FIG. 3B  is a view when viewed from the front side of the sheet processing apparatus. 
     As shown in  FIGS. 2A, 2B, 3A, and 3B , the binding unit  60  includes a water addition pressurizing portion  80  that adds water to the sheet and includes a group of vertically moving pressurizing teeth  82  shown in  FIGS. 5A and 5B  of a pair of groups of pressurizing teeth, a receiving teeth portion  126  that includes receiving teeth  130 , and a liquid replenishing pump portion (liquid replenishing pump unit)  150  that adds water to the sheet. One group of pressurizing teeth (upper pressurizing teeth)  82  constituting the pair of groups of pressurizing teeth is provided in a pressurizing teeth support portion  84  by being surrounded by an elastic member  92  formed by a rubber plate or the like. 
     The receiving teeth  130  as the other group of pressurizing teeth (lower pressurizing teeth) are supported by a receiving teeth support portion  128  to form the receiving teeth portion  126 . The pressurizing teeth  82  and the receiving teeth  130  are located to sandwich the sheets (sheet bundle) placed on the processing tray  58 . When performing binding processing, the pressurizing teeth  82  abut against the outermost sheet of the sheet bundle, and the receiving teeth  130  abut against the lowermost sheet of the sheet bundle. Then, the pressurizing teeth  82  and the receiving teeth  130  pressurize the sheet bundle. 
     As shown in  FIG. 3B , a cylinder  90  forming a liquid reservoir  88  shown in  FIGS. 5A and 5B  that holds the liquid to be applied to the sheet is arranged on the rear side of the pressurizing teeth  82 . Above the cylinder  90 , a cylinder guide  108  is located on the outer side in the circumferential direction of a pressurizing piston  104  (to be described later). The pressurizing piston  104  and the cylinder  90  form a pressurizing member (water addition member) of the liquid to be applied. 
     On the lower side, the receiving teeth  130  are supported by the receiving teeth support portion  128 , and the receiving teeth support portion  128  also supports the lower surface of the sheet. A drain tray  133  that receives the residual liquid applied to the sheet is arranged below the receiving teeth support portion  128 . 
     As is apparent from  FIG. 3A , the liquid replenishing pump unit  150  serving as a liquid replenishing pomp portion that replenishes the liquid to the liquid reservoir  88  is stored in an outer frame  120  of the binding unit  60  in adjacent to the rear sides of the pressurizing teeth  82  and the receiving teeth  130 . Although the liquid replenishing pump unit  150  will be described later, the liquid replenishing pump unit  150  includes a liquid replenishing piston portion  154  that supplies the liquid to the liquid reservoir  88 , a liquid replenishing head portion  156  that moves the liquid replenishing piston portion  154 , and a liquid replenishing tank portion  152  formed by a liquid replenishing tank  174  that stores the liquid to be replenished. In  FIG. 2A , a pump holding cover  192  that covers the liquid replenishing tank  174  can be seen. 
     Compression springs  96  are arranged on the left and right of the cylinder  90  forming the liquid reservoir  88  between a press plate  102  that vertically moves the pressurizing teeth  82  and the pressurizing teeth support portion  84  that supports the pressurizing teeth  82  and the elastic member (rubber plate)  92 . 
     The press plate  102  is driven by the driving motor (the binding motor  60 M shown in  FIG. 19 ) arranged in a space partitioned by the receiving teeth support portion  128  and the outer frame  120 . Driving from the binding motor  60 M to the press plate  102  is configured as follows. That is, an intermediate gear  138  is engaged with a motor output shaft gear  136  provided in the output shaft of the binding motor  60 M as a driving motor in the outer frame  120  on the rear side, as shown in  FIGS. 2A and 3A . 
     Rotation of the intermediate gear  138  is transferred to a cam gear  140  that rotates on a moving cam  145  and a pinion gear  142  that moves a support rack  144  to a position which is not a position where the liquid replenishing tank bottom portion  175  is supported. Note that the pinion gear  142  includes a pinion gear  142   a  that rotates together with the shaft by receiving transfer from the intermediate gear  138  and a pinion gear  142   b  that transfers the rotation to the support rack  144  via a one-way clutch  147  with the rotation shaft. This selects, based on the rotation direction of the binding motor  60 M, whether to move the support rack  144 , and operates the liquid replenishing piston portion  154  only when necessary. This point will be described later. 
     The moving cams  145  are arranged on the front and rear sides of the outer frame  120 . Pivot arms  134  that are moved by the moving cams  145  are attached to both the sides to pivot about arm fulcrums  146  attached to the outer frame  120 . Each pivot arm  134  is maintained in a state in which an arm proximal end  143  abuts against the moving cam  145  all the time by a return spring  149  stretched with the outer frame  120 . 
     On the other hand, an upper moving pin  110  of the press plate  102  is inserted into arm distal end slits  148  on the distal ends of the pivot arms  134 . Therefore, if the moving cams  145  rotate, the distal ends of the pivot arms  134  vertically move to move the press plate  102  vertically. Note that on the front side (the side of the pressurizing teeth  82 ) of the press plate  102 , the upper moving pin  110  and a lower moving pin  112  of the press plate  102  are inserted into guide slits  124  of the outer frame  120 . 
     On the rear side (the side of the liquid replenishing pump unit  150 ) of the press plate  102 , a rear guide pin  116  is also inserted into the guide slits  124  of the outer frame  120 . Since the upper moving pin  110  is also inserted into the arm distal end slits  148  of the pivot arms  134 , the press plate  102  is configured to be vertically moved by the pivot arms  134 . Therefore, the press plate  102  and the pivot arms  134  form a moving member. 
     The press plate  102  vertically moves the water addition pressurizing portion  80 . This will be described with reference to  FIGS. 4A to 7B .  FIGS. 4A and 4B  are perspective views of the water addition pressurizing portion  80  of the binding unit.  FIG. 4A  is a perspective view when viewed from the side and  FIG. 4B  is a perspective view when viewed from slightly above.  FIGS. 5A and 5B  are sectional views for explaining the water addition pressurizing portion  80 .  FIG. 5A  shows a front view and  FIG. 5B  shows a side view. 
     The water addition pressurizing portion  80  includes the press plate  102 , the pressurizing teeth support portion  84 , and the compression springs  96  existing between the press plate  102  and the pressurizing teeth support portion  84 . On the side of the pressurizing teeth support portion  84  which contacts the sheet, the pressurizing teeth  82  and the elastic member  92  formed from a rubber plate that surrounds the pressurizing teeth  82  are provided. On the rear side (pressurizing teeth rear side) of the pressurizing teeth  82 , the cylinder  90  formed integrally with the pressurizing teeth support portion  84  is provided, and guide bars  94  around which the compression springs  96  are wound are provided on both the sides of the cylinder  90 . The distal ends of the guide bars  94  are inserted through guide holes  114  of the press plate  102  all the time. 
     As shown in  FIGS. 5A and 5B , the liquid reservoir  88  that holds the liquid to be applied to the sheet is formed in a portion of about ⅓ of the height of the cylinder  90 . In the cylinder  90 , a notch is formed as a replenishment port  98  that receives the liquid from the liquid replenishing pump unit  150  (to be described later). In  FIGS. 5A and 5B , the pressurizing teeth  82  are also integrally formed, and supply holes (supply tubes)  86  are opened in the pressurizing teeth  82  so as to apply the liquid of the liquid reservoir  88  to the sheet. 
     Above the cylinder  90 , the pressurizing piston  104  that is pressurized and moved so as to apply the liquid of the liquid reservoir  88  from the supply holes of the pressurizing teeth  82  by being inserted into the cylinder  90  to pressurize the liquid is located. This pressurizing piston  104  is fixed to the press plate  102  at the upper end. A piston packing  106  is circumferentially wound around the insertion portion of the pressurizing piston  104  into the cylinder  90 . The piston packing  106  shown in  FIGS. 5A and 5B  is wound around one portion. However, if the piston packing  106  is wound around each of two or more portions, pressure when applying the liquid can be made high. 
     The moving cylinder guide  108  is provided outside the cylinder  90  in the press plate  102  to make it possible to smoothly insert the pressurizing piston  104  and perform an application operation of pressurizing the liquid. The guide holes  114 , and the upper moving pin  110 , the lower moving pin  112 , and the rear guide pin  116  all of which are inserted into the guide slits  124  of the outer frame  120  are stationarily provided in the press plate  102 . Among them, the upper moving pin  110  is extended outward longer than the remaining pins. This is to make it possible to insert the upper moving pin  110  into the arm distal end slits  148  of the pivot arms  134  that pivot outside the outer frame  120 . 
       FIGS. 6A, 6B, 7A, and 7B  show a state in which the water addition pressurizing portion  80  having the above arrangement is compressed by the pivot arms  134 .  FIG. 6A  is a perspective view when viewed from slightly above, and  FIG. 6B  is a perspective view when viewed from below. The operation of the pivot arm  134  for setting this compressed state will be described later with reference to  FIGS. 14A to 14C  and  FIGS. 13A to 13C . 
     In the views of the compressed state, the press plate  102  abuts against the receiving teeth support portion  128  by the pivot arms  134 , the compression springs  96  wound around the guide bars  94  are compressed, and the guide bars  94  protrude from the guide holes  114 .  FIG. 6B  is a view when viewing this state from the side of the receiving teeth support portion  128 . The pressurizing teeth  82  provided with the supply holes (supply tubes)  86  are surrounded by the elastic member  92  formed by a rubber plate or the like. This is done to prevent the liquid, applied to a portion except for a range where pressure bonding is performed by the pressurizing teeth  82 , from spreading when the liquid of the liquid reservoir  88  is applied by the pressurizing piston  104  after the pressurizing teeth support portion  84  presses the sheet bundle. 
       FIGS. 7A and 7B  are sectional views of the water addition pressurizing portion  80 .  FIG. 7A  is a front cross-sectional view of the cylinder  90  and the guide bars  94 .  FIG. 7B  is a sectional view when cutting the cylinder  90  in a direction intersecting  FIG. 7A . In  FIGS. 7A and 7B , the liquid held in the liquid reservoir  88  of the cylinder  90  is applied to the outermost sheet of the sheet bundle by the pressurizing piston  104  through the supply holes (supply tubes)  86  of the pressurizing teeth  82 , and penetrates into the sheet bundle. The sheets are pressed by receiving the force of the press plate  102  by the pressurizing piston  104  and pressure-bonded so as to mesh, with the receiving teeth  130 , the sheet bundle into which the liquid has penetrated. 
     Note that the cylinder  90  is formed to have an inner diameter which is decreased as the pressurizing piston  104  moves from above, and the liquid reservoir  88  that holds the liquid to be applied to the sheet is formed in a portion of about ⅓ of the height of the cylinder  90 , as described above. The liquid reservoir  88  is pressurized by the pressurizing piston  104  from the position, thereby applying the liquid. On the upper side, the liquid discharged and replenished from the liquid replenishing pump unit  150  is received from the replenishment port  98  into the liquid reservoir  88 , thereby waiting for the next operation of the pressurizing piston  104 . Therefore, the amount of liquid applied to the sheet at once corresponds to the amount of liquid held in the liquid reservoir  88 . 
     [Liquid Replenishing Pump Portion] 
     The liquid replenishing pump unit  150  as a liquid replenishing pump portion that replenishes the liquid to the liquid reservoir  88  through the replenishment port  98  will be described next with reference to  FIGS. 8 to 10 . The liquid replenishing pump unit  150  is internally provided in the outer frame  120  of the binding unit  60 , similar to the pressurizing teeth support portion  84  and the receiving teeth portion  126 , as already described with reference to  FIGS. 2A and 2B . Therefore, it is unnecessary to lay a liquid replenishing pipe and the like from the outside of the binding unit  60 , and the apparatus is easy to deal with and is compact. 
     The liquid replenishing pump unit  150  will be described with reference to the accompanying drawings.  FIG. 8  is a sectional view for explaining the liquid replenishing pump unit  150 .  FIG. 9  is an exploded perspective view of the liquid replenishing piston portion  154  as an important constituent element of the liquid replenishing pump unit  150 , and an enlarged view for explaining the liquid replenishing piston portion  154 .  FIG. 10  is an enlarged view for explaining a water discharge state. 
     As shown in  FIG. 8 , the liquid replenishing pump unit  150  includes the liquid replenishing head portion  156  that is pressed by the press plate  102  to vertically move, the liquid replenishing piston portion  154  that temporarily holds the liquid and discharges the liquid to the liquid replenishing head portion  156 , and the liquid replenishing tank portion  152  that stores the liquid to be replenished to the liquid replenishing piston portion  154 . The liquid discharged from the liquid replenishing piston portion  154  when the liquid replenishing head portion  156  vertically moves is replenished, to the liquid reservoir  88 , from a liquid replenishing joint portion  158  whose protruding port is extended from the liquid replenishing head portion  156  to the replenishment port  98  of the water addition pressurizing portion  80 . 
     In the liquid replenishing tank portion  152 , a moving plate  176  that moves along with the decrease of the liquid every time the liquid is discharged to the liquid replenishing joint portion  158  can be vertically moved by the liquid replenishing piston portion  154  to be described with reference to  FIGS. 9 and 10 . Furthermore, an air hole  178  that allows the movement of the moving plate  176  is formed in a liquid replenishing tank bottom portion  175  of the liquid replenishing tank portion  152 . 
     The liquid replenishing piston portion  154  that discharges the liquid to the liquid replenishing head portion  156  will be described next with reference to  FIG. 9 . The liquid replenishing piston portion  154  is provided with a tank cap  172  that is threadably engaged with the liquid replenishing tank portion  152  and a liquid replenishing cylinder  167  that is fixed to the tank cap  172  to temporarily hold the liquid of the liquid replenishing tank portion  152 . Note that a sealing  171  is provided between the tank cap  172  and a liquid replenishing tank  174  of the liquid replenishing tank portion  152 . Note that the tank cap  172  is supported in the binding unit  60  by being fitted in a curved portion ( FIGS. 4A, 4B, 6A, and 6B ) below the replenishment port  98  of the pressurizing teeth support portion  84 . 
     Furthermore, an upper piston  162  that similarly moves along with the vertical movement of the liquid replenishing head portion  156  is provided above the liquid replenishing cylinder  167 . An upper spring  169  is wound around the upper piston  162 , and a pump valve  165  around which the upper spring  169  is similarly wound is arranged below the upper piston  162 . Inside the pump valve  165 , a lower piston  163  around which a lower spring  170  is wound is located between the pump valve  165  and the lower portion of the liquid replenishing cylinder  167 . A lower piston protruding portion  164  that pressure-bonds and seals the pump valve  165  is provided in the circumferential direction of the upper piston  162 . Sealing of the lower piston protruding portion  164  is implemented by the lower spring  170 . 
     At the lower end of the liquid replenishing cylinder  167 , a ball valve  166  that takes in the liquid of the liquid replenishing tank  174  and seals the liquid replenishing cylinder  167  is provided. If the internal pressure in the liquid replenishing cylinder  167  increases, the ball valve  166  is located at the lower end of the liquid replenishing cylinder  167 . If the internal pressure decreases, the ball valve  166  slightly moves upward to take in the liquid of the liquid replenishing tank  174 . 
     As shown in  FIG. 10 , if the above-described liquid replenishing pump unit  150  lowers when the liquid replenishing head portion  156  is pressed by the press plate  102 , the upper piston  162  also lowers. This also presses the upper spring  169  winding around the upper piston  162 , thereby pressing the pump valve  165 . When the pump valve  165  lowers, the internal pressure of the liquid replenishing cylinder  167  increases since the ball valve  166  seals the lower end. 
     If the internal pressure of the liquid replenishing cylinder  167  exceeds a predetermined value, the liquid replenishing cylinder  167  and the upper spring  169  winding around the upper piston  162  are compressed by the internal pressure, thereby generating a gap between the pump valve  165  and the lower piston protruding portion  164 . The liquid of the liquid replenishing cylinder  167  is discharged through the gap from the liquid replenishing joint portion  158  of the liquid replenishing head portion  156  to the liquid reservoir  88  via the pump valve  165 , the upper portion of the lower piston  163 , and the upper piston  162 , as indicated by arrows in  FIG. 10 . If the liquid of the liquid replenishing tank  174  decreases, the moving plate  176  rises due to the decrease in pressure of the liquid replenishing tank  174 , thereby making the liquid level in the liquid replenishing tank  174  constant all the time. 
     As described above, every time the press plate  102  is pressed, the liquid of the liquid replenishing tank  174  is replenished to the replenishment port  98  of the water addition pressurizing portion  80  via the liquid replenishing joint portion  158 . 
     The pressure-bonding binding operation of the sheet bundle placed on the processing tray  58  in the binding unit  60  will be described below. When performing pressure bonding by a pair of groups of pressurizing teeth (the pressurizing teeth  82  and the receiving teeth  130 ), the binding unit  60  can selectively execute one of pressure bonding without applying any liquid (pressure-bonding binding without water addition) and pressure bonding after applying the liquid to a pressure-bonding portion (water-addition pressure-bonding binding). For example, the above processing may be executable in accordance with a selection operation by the user on a setting screen. 
     [Binding with Water Addition (Water-Addition Pressure-Bonding Binding)] 
     A water-addition pressure-bonding binding operation of performing binding by adding the liquid to a pressure-bonding range before pressure bonding by the pressurizing teeth  82  will be described with reference to  FIGS. 11A to 13C .  FIGS. 11A to 11C  are views for explaining states when viewed from the front side of the binding unit  60 .  FIGS. 12A to 12C  are views for explaining the states when viewed from the rear side.  FIGS. 13A to 13C  are sectional views for explaining water-addition pressure-bonding binding.  FIGS. 11A, 12A, and 13A  each show a state in which the pressurizing teeth support portion  84  (pressurizing teeth  82 ) is separated from the sheet.  FIGS. 11B, 12B, and 13B  each show a state when the pressurizing teeth support portion  84  (pressurizing teeth  82 ) is in press contact with the sheet.  FIGS. 11C, 12C, and 13C  each show a state in which pressure bonding is performed by applying the liquid to the sheet. 
       FIGS. 11A, 12A, and 13A  each show the sheet acceptance initial time at which the sheets are placed on the processing tray  58 , exist between the pressurizing teeth  82  and the receiving teeth  130  of the binding unit  60 , and are placed on the receiving teeth support portion  128 . In  FIGS. 11A to 11C and 12A to 12C , the sheets are not illustrated, and  FIGS. 13A to 13C  show a state in which the sheets are stacked. When the designated number of sheets are placed on the receiving teeth support portion  128  including the receiving teeth  130 , driving of the binding motor  60 M starts. In this case, with respect to the rotation direction of the binding motor  60 M, to add water, the binding motor  60 M rotates in a direction opposite to the direction in which pressure bonding is performed without adding water as shown in  FIGS. 14A to 14C, 15, and 16 . The number of placed sheets is larger than five, and is, for example, eight in this embodiment. 
     That is, in this example, since binding with water addition is performed, the binding motor  60 M is driven in a direction in which the moving cam  145  pivots in a counterclockwise direction on the front side and the moving cam  145  pivots in a clockwise direction on the rear side (a clockwise-direction driving motor in  FIGS. 12A to 12C ). Since each moving cam  145  has a symmetric shape centered on a rotation position, the protruding side of the moving cam  145  moves in a direction to press the distal end of the pivot arm  134 . On the other hand, the action of the one-way clutch  147  causes the pinion gear  142  (pinion gear  142   b ) engaged with the intermediate gear  138  to start moving in a direction to support the liquid replenishing tank bottom portion  175  by a projecting portion  141  of the support rack  144 . 
     In this example, by one-way rotation (in  FIGS. 12A to 12C , rotation in the clockwise direction) of the binding motor  60 M, the one-way clutch  147  intervening between the pinion gear  142  (pinion gear  142   b ) and the shaft meshes to move the support rack  144  to a position at which the liquid replenishing tank bottom portion  175  is supported. This movement fixes the liquid replenishing tank bottom portion  175 . If the liquid replenishing head portion  156  is pressed by the press plate  102 , the liquid replenishing piston portion  154  operates, thereby making it possible to supply water in the liquid replenishing tank  174  to the liquid reservoir  88  via the liquid replenishing joint portion  158 . Note that as shown in  FIGS. 13A to 13C , a rack return spring  139  that returns to the original position when the shaft reversely rotates to release engagement intervenes between the support rack  144  and the outer frame  120 . 
     Subsequently, in  FIGS. 11B, 12B, and 13B , the press plate  102  lowers to bring the pressurizing teeth support portion  84  including the pressurizing teeth  82  into tight contact with the outermost sheet of the sheet bundle. If, in this state, the press plate  102  is pressurized, the compression springs  96  intervening between the press plate  102  and the pressurizing teeth support portion  84  press the pressurizing teeth support portion  84  against the sheet. The pressurizing teeth support portion  84  is provided, on the side of the pressurizing teeth  82 , with the elastic member (rubber plate)  92  surrounding the pressurizing teeth  82 , and the elastic member  92  is brought into press contact with the sheet not to generate a gap between the pressurizing teeth  82  and the sheet surface. In this example, a setting is made so that a force of 70 kgf to 100 kgf acts on the sheet. Note that at this stage, the liquid reservoir  88  holds the liquid by the operation of the liquid replenishing piston portion  154 . Since, however, the pressurizing piston  104  has not reached a pressurizing position with respect to the cylinder  90 , water addition by pressurization is not performed. 
     In the state shown in  FIGS. 11C, 12C, and 13C , the pivot arms  134  are moved by the moving cams  145  to lower the press plate  102  in a state in which the pressurizing teeth support portion  84  is in tight contact with the sheet. Then, the pressurizing piston  104  is inserted into the cylinder  90  to add the liquid of the liquid reservoir  88  to the sheet from the supply holes (supply tubes)  86  of the pressurizing teeth  82 . Even after completion of water addition, the press plate  102  moves in a direction to pressure-bond the sheets by the moving cams  145 , and thus the pressurizing piston  104  presses the pressurizing teeth  82  toward the receiving teeth  130  to pressure-bond the sheets. Pressure bonding at this time can be possible by a force of 300 kgf to 400 kgf which is weaker than the pressure-bonding force without water addition. In this example, a voltage to the binding motor  60 M is controlled to set a force of 350 kgf, thereby generating a pressurizing force. 
     As already described, the liquid replenishing pump unit  150  replenishes the liquid from the liquid replenishing piston portion  154  to the liquid reservoir  88  by sandwiching the liquid replenishing head portion  156  and the liquid replenishing tank bottom portion  175  with the support rack  144 , and pressing the liquid replenishing head portion  156 . That is, as shown in  FIGS. 13B and 13C , the support rack  144  is located in the liquid replenishing tank bottom portion  175 , and the liquid replenishing pump unit  150  is fixed. This discharges the liquid from the liquid replenishing piston portion  154 , thereby replenishing the liquid to the liquid reservoir  88 . Note that water-addition pressure-bonding binding is performed for eight sheets on the processing tray  58 . 
     [Pressurizing Teeth and Receiving Teeth of Water Addition Pressurizing Portion] 
     The pressurizing teeth  82  of the water addition pressurizing portion  80  and the receiving teeth  130  will be described with reference to  FIGS. 14A to 14C . The meshing state and the positions of the supply holes (supply tubes)  86  will be described with reference to  FIG. 15 .  FIG. 14A  is a plan view for explaining the pressurizing teeth. As described above, the cylinder  90  that holds the liquid to be added to the sheet is provided on the rear side of the pressurizing teeth  82  which meshes the sheet. The cylinder  90  is formed in a columnar shape which is partially cut, and includes a range (the range of the liquid reservoir  88 ) where the pressurizing piston  104  pressurizes the liquid to add it, and a liquid replenishing port  118  that has a diameter larger than that of the range and receives an insertion guide of the pressurizing piston  104  and the liquid from the liquid replenishing pump unit  150 . 
       FIG. 14B  is a sectional view for explaining the pressurizing teeth  82  and the receiving teeth portion  126  indicated by a two-dot dashed line in  FIG. 14A . As is apparent from  FIG. 14B , the pressurizing teeth support portion  84  is obtained by integrally forming the pressurizing teeth  82 , the cylinder  90  on the rear side, and the guide bars  94 . This secures the strength and ease of assembly. The receiving teeth  130  (receiving teeth portion  126 ) that mesh with the pressurizing teeth  82  and the drain tray  133 , below the receiving teeth  130 , that temporarily holds the remaining added liquid (residual liquid) are provided at a position opposite to the pressurizing teeth support portion  84 . 
     Then, the supply holes (supply tubes)  86  for making it possible to add the liquid of the liquid reservoir  88  to the sheet are formed at a plurality of positions in the inclined portions of the pressurizing teeth  82 . Furthermore, communicating holes  132  to the outside, through which air at the time of pressing the sheet by the pressurizing teeth support portion  84  and the residual liquid at the time of water addition pass, are formed in the inclined portions of the receiving teeth  130 . Note that the communicating holes  132  are formed to have passage volumes larger than those of the supply holes (supply tubes)  86  so as to efficiently bleed air and draw the residual liquid. 
       FIG. 14C  is a view of the pressurizing teeth support portion  84  when viewed from the bottom surface on the side of the pressurizing teeth  82 . The elastic member  92  that is made of a rubber material and surrounds the pressurizing teeth  82  is bonded to the pressurizing teeth support portion  84 . This eliminates a gap around the pressurizing teeth  82  in a step of pressing the pressurizing teeth support portion  84  against the sheet by the compression springs  96 , thereby reducing the applied liquid to spread outside the pressurizing region undergoing pressure bonding. 
     [Arrangement of Supply Holes (Supply Tubes) and Communicating Holes] 
     The supply holes (supply tubes)  86  formed in the pressurizing teeth  82  and the communicating hole  132  to the outside (drain tray  133 ) formed in the receiving teeth  130 , which are shown in  FIGS. 14A to 14C , will be described with reference to  FIG. 15 .  FIG. 15  is an enlarged view for explaining the pressurizing teeth  82  and the receiving teeth  130 . The pressurizing teeth  82  include ridge portions  82   a  protruding to the receiving teeth  130 , concave valley portions  82   b , and inclined portions  82   c  forming them so as to form a three-dimensional structure in the sheet bundle by meshing with the receiving teeth  130  to tangle fibers. The receiving teeth  130  similarly includes receiving ridge portions  130   a , receiving valley portions  130   b , and receiving inclined portions  130   c.    
     Then, the liquid from the liquid reservoir  88  in the cylinder  90  is pressed by the pressurizing piston  104  to be discharged from the supply holes (supply tubes)  86  formed in the pressurizing teeth  82 . At this time, the supply holes  86  are arranged so that the liquid is discharged from a plurality of positions in the inclined portion  82   c , as shown in  FIG. 15 . With this arrangement, if the pressurizing teeth  82  and the receiving teeth  130  mesh with each other to form a three-dimensional structure in the sheets, as indicated by a portion surrounded a two-dot dashed line in  FIG. 15 , it is confirmed that fibers (cellulose fibers in the case of paper) of the sheets are loosened in the inclined portions  82   c  and the receiving inclined portions  130   c  (opposite arrows in  FIG. 15 ). 
     If the liquid is added to the positions of the inclined portions at which the fibers are loosened most, the liquid readily penetrates and the fibers are readily tangled by subsequent further pressurization. Thus, in this embodiment, the supply holes (supply tubes)  86  through which the liquid is added are arranged in the inclined portions  82   c  of the pressurizing teeth  82 . In addition, the communicating holes  132  whose volumes are made larger than those of the supply holes (supply tubes)  86  so as to readily bleed air and draw the residual liquid are provided in the receiving inclined portions  130   c  of the receiving teeth  130 . 
     [Pressurizing Teeth Support Portion and Receiving Teeth Support Portion] 
     The relationship between the positions of the pressurizing teeth support portion  84  and the receiving teeth support portion  128  and the position of the sheets clamped and pressed between the pressurizing teeth support portion  84  and the receiving teeth support portion  128  will be described next with reference to  FIGS. 16 and 17A to 17C .  FIG. 16  shows a sheet position when pressure-bonding binding is performed for a sheet corner portion on the front side of the processing tray  58  already described with reference to  FIG. 1 . When pressure-bonding the sheet corner portion, the sheets are located so that a pressurizing region where the pressurizing teeth  82  and the receiving teeth  130  meshing with the pressurizing teeth  82  pressurize the sheets is included in the sheets. In addition, the sheet position is restricted so that the pressurizing teeth support portion  84  supporting the pressurizing teeth  82  and the receiving teeth support portion  128  supporting the receiving teeth  130  are located outside the sheet corner portion by L 3 . Together with this, the pressurizing teeth support portion  84  and the receiving teeth support portion  128  abut against a position, at which no water is added (the added water does not penetrate), on a sheet gravity side by L 2  with respect to a position at which the liquid added from the pressurizing teeth  82  penetrates. 
       FIGS. 17A to 17C  are views each showing the relationship between an application region where the liquid is applied to the sheet and the pressurizing region of the sheet by the pressurizing teeth  82  and the receiving teeth  130 . It is possible to improve the pressure-bonding force of the sheet bundle by making the application region and the pressurizing region overlap each other, as compared with a case in which no liquid is applied. 
       FIG. 17A  is a sectional view taken along a line Sc in  FIG. 16 . In  FIG. 17A , the pressurizing teeth  82  and the receiving teeth  130  pressurize an application region L 1 . 
     Referring to  FIG. 17B , the application region L 1  intrudes on the sheet gravity side by exceeding the range of the pressurizing region. In this case as well, it is possible to improve the pressure-boding force of the sheet bundle. However, a state in which the fibers of the sheets are loosened by water addition is maintained. Therefore, at a position on the sheet gravity side, the sheets are readily torn. If the sheet applied with the liquid is left without being pressurized, the application region of the sheet is wrinkled, thereby worsening the appearance. 
     Referring to  FIG. 17C , the application region L 1  is larger than the pressurizing region, and protrudes to the sheet end portion side (a portion L 5 ). In this case as well, it is possible to improve the pressure-bonding force of the sheet bundle. However, the sheet end portions which are not pressurized tend to fall apart. As shown in  FIG. 17A , it is possible to improve the binding force of the sheet bundle without degrading the outer appearance of the sheet bundle by arranging the sheet bundle so that the application region becomes part of the pressurizing region. 
     Note that the above description indicates the front side of the processing tray  58  described with reference to  FIG. 1 . However, the same effect is obtained by processing the sheets on the rear side of the processing tray  58  in the same manner, as a matter of course. 
     The number of sheets to undergo pressure bonding and liquid application and a predetermined number of sheets as a reference for separating a case in which the pressure bonding is performed without applying the liquid, as described with reference to  FIGS. 13A to 13C and 14A to 14C , and a case in which water-addition pressure-bonding binding of performing pressure bonding by applying the liquid is performed will be described with reference to  FIG. 18A to 18D . 
       FIG. 18A  is a view for explaining the relationship between the pressurizing teeth and the predetermined number of sheets, and schematically shows a case in which the upper teeth of a pair of groups of pressurizing teeth are the pressurizing teeth  82  and the lower teeth are the receiving teeth  130 . As shown in  FIG. 18A , the three-dimensional structure is formed in the sheets by a difference in height between the teeth meshing with each other, in other words, by a distance between the peak of the ridge portion  82   a  and the bottom of the valley portion  82   b . The height is normally about 0.4 mm to 0.6 mm, and is set to 0.5 mm for meshing between the pressurizing teeth  82  and the receiving teeth  130 . 
     On the other hand, a sheet used as a normal copy sheet is 68 g/m 2  paper and has a thickness lp of about 0.1 mm. Therefore, to form a three-dimensional structure without applying the liquid to the sheet, five sheets are appropriate. If the number of sheets exceeds five, the pressure-bonding force of the sheets bound without applying the liquid is weakened. Therefore, the predetermined number of sheets that undergo pressure-bonding binding without applying the liquid by the water-addition pressure-bonding binding unit  60  is set to five. When binding sheets, the number of which exceeds five, water-addition pressure-bonding binding is performed to pressure-bond sheets by applying the liquid to the sheet and temporarily loosening fibers of the sheets. As another form, if the difference in height between the teeth meshing with each other is 0.6 mm, the predetermined number of sheets is six, and if the difference in height is 0.4 mm, the predetermined number of sheets is four. 
     As described above, when binding sheets, the number of which is equal to or smaller than the predetermined number, pressure-bonding binding is performed without applying the liquid. When binding sheets, the number of which exceeds the predetermined number, water-addition pressure-bonding binding is performed by applying the liquid. As described above, water-addition pressure-bonding binding may be performed only if the pressure-bonding force decreases due to binding without applying the liquid. 
     [Explanation of Control Arrangement] 
     The control arrangement of an image forming system  1  will be described with reference to a block diagram shown in  FIG. 19 . The image forming system  1  shown in  FIG. 19  includes an image forming apparatus and the sheet processing apparatus. The image forming apparatus includes an image forming control unit  200  that comprehensively controls the image forming apparatus. The sheet processing apparatus includes a sheet processing control unit  205  (including a control CPU) that comprehensively controls the sheet processing apparatus. 
     In the image forming apparatus, the image forming control unit  200  is communicably connected to a feeding control unit  202  and an input unit  203 . A mode setting unit  201  sets an operation mode by selectively accepting, from a control panel  26  provided in the input unit  203 , setting of (1) printout mode, (2) job sorting mode, (3) binding processing mode, (4) bookbinding (saddle stitch) processing mode, or (5) manual binding mode. 
     The sheet processing control unit  205  includes the control CPU, and operates the sheet processing apparatus in accordance with the operation mode (sheet processing mode) set by the mode setting unit  201 . The sheet processing control unit  205  is communicably connected to a ROM  207  that stores an operation program and a RAM  206  that stores control data. The sheet processing control unit  205  acquires detection information from various sensor input units  220 . 
     [Various Sensor Input Units] 
     The various sensor input units  220  include an entrance sensor  38  that detects conveyance of a sheet on which an image has been formed from the image forming apparatus, and manages various main motor driving operations by detecting the leading and trailing edges of a sheet. On the downstream side of the entrance sensor  38 , a sheet sensor  39  that detects a sheet jam is located. In the processing tray  58 , a processing tray empty sensor  58 S that detects whether a sheet is placed is provided. Then, a stack tray position sensor  34 S that detects a paper surface of a stack tray  34  for accumulating a sheet discharged by a discharge roller while gradually moving downward is provided. In addition to these sensors, a sensor that detects the position of a punch unit or the binding unit  60 , a sensor that detects the operation of a saddle stitch unit, and the like may be provided. 
     [Output Units of Various Motors] 
     A conveyance control unit  210  that conveys a sheet is provided in the above-described sheet processing control unit  205 . The conveyance control unit  210  controls a loading roller motor  41 M for loading a sheet, a conveyance roller motor  48 M for conveying the sheet to the processing tray  58 , and a discharge roller motor  52 M for discharging the sheet from the processing tray  58 . 
     Furthermore, a punch control unit  211  is provided to perform punching processing for the trailing edge of the sheet loaded by a loading roller driven by the loading roller motor  41 M. The punch control unit  211  controls a punch motor  40 M that performs punching at a designated position in the width direction of the sheet. A processing tray control unit  212  controls an alignment plate motor  59 M for moving the alignment plate  59  that aligns the sheet conveyed to the processing tray  58  by sandwiching the sheet from two sides in the sheet width direction. 
     A binding control unit  213  controls a binding motor  60 M and a binding unit moving motor  60 SM that moves the binding unit  60  to the designated position in the sheet width direction, thereby performing 2-point binding or corner binding, as shown in  FIG. 1 . The bound sheet bundle is discharged to the stack tray  34  by the discharge roller driven by a bundle moving belt and the discharge roller motor  52 M. At this time, a tray vertical movement control unit  214  controls a stack tray motor  34 M by detection of the stack tray position sensor  34 S so that the position of the upper surface of the sheet is always fixed with respect to the discharge port. 
     The sheet processing control unit  205  may include a block except for the blocks shown in  FIG. 19 . For example, blocks corresponding to executable postprocessing such as a stacker control unit  215  for bookbinding (saddle stitch) processing, a saddle stitch control unit  216  for performing saddle stitch, and a folding/discharge control unit  217  may be provided. 
     Note that in each of the binding processing mode and the manual binding mode, a water-addition binding mode of performing binding by adding water to a binding position and a non-water-addition binding mode of performing binding without adding water can be executed. The sheet processing control unit  205  acquires bound sheet count information from the image forming control unit  200 , and sets the water-addition binding mode or the non-water-addition binding mode in accordance with the number of sheets. 
     If a determination unit that determines whether the number of bound sheets is equal to or smaller than the predetermined number or exceeds the predetermined number may be implemented by the binding control unit  213 , the sheet processing control unit (control CPU)  205 , or the image forming control unit  200 . Furthermore, the sheet bundle that clamped and pressurized by the pressurizing teeth  82  and the receiving teeth  130  may be measured by a known method and converted into the number of sheets, and the water-addition binding mode and the non-water-addition binding mode may be switched in accordance with the number of sheets of the sheet bundle. 
     The present invention is not limited to the above-described embodiment and various changes and modifications can be made without departing from the spirit and scope of the present invention. To apprise the public of the scope of the present invention, the following claims are made. Although the above embodiment indicates a preferable example, those skilled in the art can implement various alternate examples, corrected examples, modified examples, or improved examples from contents disclosed in this specification, and these examples are included in the technical scope described in the appended claims. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2019-073708 filed Apr. 8, 2019 and Japanese Patent Application No. 2020-058247 filed Mar. 27, 2020, which are hereby incorporated by reference herein in their entirety.