Patent Publication Number: US-7722023-B2

Title: Bookbinding apparatus and bookbinding system

Description:
This application is based on Japanese Patent Application No. 2007-248797 filed on Sep. 26, 2007 in Japanese Patent Office, the entire content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a bookbinding apparatus to make a booklet by coating adhesive on a spine of a sheet bundle and to a bookbinding system equipped with the aforesaid bookbinding apparatus and with an image forming apparatus that forms images on a sheet. 
     A bookbinding apparatus for binding a sheet bundle composed of a plurality of sheets through gluing which is conducted by moving a coating device along a spine of the sheet bundle has been developed as a small-sized binding apparatus. 
     In particular, the aforesaid bookbinding apparatus has been developed as s small-sized bookbinding apparatus to be used for a bookbinding system wherein an image forming progress for forming an image on a sheet with an image forming apparatus and a bookbinding progress for binding sheets are conducted in a continuous progress. 
     For example, in Japanese Patent Publication Open to Public Inspection No. 2006-346984, there is proposed a bookbinding apparatus for conducting coating by moving a coating device along a spine of a sheet bundle wherein coating is conducted through first coating operations by bringing the coating device into contact with a spine of the sheet bundle under strong contact pressure and through second coating operations under weak contact pressure. 
     The bookbinding apparatus in Japanese Patent Publication Open to Public Inspection No. 2006-346984 conducts the aforesaid first and second coating operations for the purpose of making adhesion between sheets constituting a sheet bundle to be sure and of making adhesion of a cover to be sure. 
     By changing a thickness of coating of an adhesive layer formed on a spine of a sheet bundle depending on a thickness of a booklet, it is possible to produce a high-quality booklet, and thereby the quality is stabilized. 
     The reasons for the foregoing are as follows. 
     In the case of a thick booklet, it is necessary to make a coating thickness to be thick for obtaining necessary adhesive strength. However, if a coating thickness is made to be thick in the same way in the case of a thin booklet, adhesive is squeezed out as side adhesive when wrapping with a cover, resulting in excessive adhesive and poor binding. 
     On the other hand, when a booklet is thin, sufficient adhesive strength can be obtained even when a coating thickness is relatively thin. 
     As is suggested in Japanese Patent Publication Open to Public Inspection No. 2006-346984, changing coating conditions depending on a thickness of a sheet bundle is a powerful technique to solve the aforesaid problems. In other words, by changing a coating amount of adhesive depending on a thickness of a sheet bundle, the problems mentioned above can be solved to a certain extent. 
     However, when conducting coating control based on a thickness of a sheet bundle, a thickness of a formed adhesive layer is changed for each sheet bundle, and an external form of a sheet bundle or an external form of a booklet prepared by joining a cover on a sheet bundle shows lack of uniformity, which is a problem. 
     The lack of uniformity of the sheet bundle or of the booklet is especially remarkable in the following occasions. 
     For changing a coating weight depending on a thickness of the sheet bundle, there is employed a controlling method wherein a prescribed thickness represents a threshold value, and when a thickness is the threshold value or higher, a coating amount is increased, while, when a thickness is less than the threshold value, a coating amount is decreased. 
     When binding processing is continued for sheet bundles each having a thickness close to the threshold value, there is sometimes an occasion wherein a judgment for control of a coating thickness is changed for every sheet bundle even when the number of sheets is the same, resulting in formation of adhesive layers each being different for every sheet bundle. 
       FIG. 1  shows schematically situations of the prepared booklets wherein adhesive layers which are different in terms of a thickness are formed for every sheet bundle even when the number of sheets in a sheet bundle is the same, as described above. 
     As a result of adhesive layers N 1 -N 4  of booklets P 1 -P 4  which are different from each other in terms of a thickness, when the booklets P 1 -P 4  are aligned at the reference position of their spines, ends Q 1 -Q 4  of the booklets show lack of uniformity. 
     In other words, as a result of control of coating amount, there is caused a problem that consistency of booklets is lowered and quality of booklets is lowered. 
     SUMMARY 
     The aforesaid problems are solved by the following embodiments of the invention. 
     1. A bookbinding apparatus which coats adhesive on a spine of a sheet bundle by moving relatively the sheet bundle or a coating device which coats adhesive to the spine of the sheet bundle, the bookbinding apparatus comprising: a thickness information generating device which generates information on a thickness of the sheet bundle, a booklet information generating device which generates booklet information including at least information on the number of sheets constituting the sheet bundle, and a control device which conducts an adjustment of a coating thickness of a layer of the adhesive coated on the spine of the sheet bundle based on information on the thickness of the sheet bundle coming from the thickness information generating device and which corrects the adjustment having been conducted based on the thickness of the sheet bundle, based on the booklet information coming from the booklet information generating device.
 
2. A bookbinding system characterized by having an image forming apparatus that forms an image on a sheet and the bookbinding apparatus of Item 1 that conducts bookbinding processing for the sheets ejected from the image forming apparatus.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating fluctuations of outer shapes of booklets caused by coating thicknesses. 
         FIG. 2  is a diagram showing an overall structure of a bookbinding system. 
         FIG. 3  is a diagram showing the structure of a bookbinding apparatus illustrating forming of a sheet bundle and processes thereafter. 
         FIG. 4  is a diagram showing a structure of an adhesive coating device. 
         FIG. 5  is a perspective view showing an adhesive coating device and a sheet bundle grasped by a grasping device. 
         FIGS. 6(   a ) and  6 ( b ) are diagrams illustrating movements of an adhesive coating device. 
         FIG. 7  is a conceptual diagram showing positions of a sheet bundle conveyance device and of a cover sheet supporting device. 
         FIGS. 8(   a )- 8 ( d ) are cross-sectional views of a cover sheet supporting device and a sheet bundle showing a folding process for a cover sheet. 
         FIG. 9  is a diagram showing an adhesive coating process. 
         FIG. 10  is a block diagram of a control system that conducts control of coating thickness and conducts control of cutting of a cover sheet. 
         FIG. 11  is a flow chart of a coating thickness control in an example of the embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention will be described as follows based on an embodiment to which, however, the invention is not limited. 
       FIG. 2  is a diagram showing an overall structure of a bookbinding system relating to the embodiment of the invention. 
     The bookbinding system illustrated is composed of image forming apparatus A and bookbinding apparatus B. Incidentally, in the present embodiment, booklet reception apparatus C that receives a bound booklet is connected to the aforesaid bookbinding apparatus B. 
     First, an outline of the image forming apparatus and the bookbinding apparatus will be described. 
     &lt;Image Forming Apparatus A&gt; 
     Image forming apparatus A has an image forming device wherein charging device  2 , image exposure device  3 , developing device  4 , transfer neutralizing device  5  and cleaning device  6  are arranged around image carrier  1  that rotates. 
     After a surface of the image carrier  1  is charged evenly by the charging device  2 , the image forming device conducts exposure scanning that is based on image data which have been read out from a document by a laser beam of the image exposure device  3 , to form a latent image, and conducts reversal development for the latent image with the developing device  4  to form a toner image on a surface of the image carrier  1 . 
     Sheet S fed out of sheet storage device  7 A is conveyed to a position for transfer. After the toner image is transferred onto sheet S by the transfer neutralizing device  5  at the position for transfer, electric charges on sheet S are eliminated, and sheet S is separated from the image carrier  1  and is conveyed by conveyance device  7 B to be heated and fixed by fixing device  8  successively, and is ejected from ejection roller  7 C. 
     When forming images on both sides of sheet S, sheet S heated and fixed by the fixing device  8  is caused by conveyance path switching device  7 D to branch off a regular sheet ejection path, and is conveyed again to the image forming apparatus so that an image is formed on the reverse side of the sheet S, after it is reversed inside out on a switchback basis in reverse conveyance device  7 E. 
     Sheet S 1  subjected to fixing processing by fixing device  8  is ejected out from sheet ejection roller  7 C to the outside of the apparatus. The sheet S ejected out of the sheet ejection roller  7 C is fed into bookbinding apparatus B. 
     A surface of the image carrier  1  after image treatment is cleaned by cleaning device  6  and developing agents remaining on the surface are removed, thus, the surface becomes ready for the following image forming. 
     On the upper portion of image forming apparatus A, there is arranged operation display device  9  that is equipped with an input device and a display device. 
     &lt;Bookbinding Apparatus B&gt; 
     Bookbinding apparatus B is equipped with sheet conveyance device  10 , sheet ejection device  20 , sheet bundle reception device  30 , sheet bundle conveyance device  40 , adhesive coating device  50 , cover supply device  60 , cover cutting device  70 , cover supporting device  80  and operation display device  90 . 
     The sheet S on which an image is formed by image forming apparatus A is conveyed by sheet conveyance device  10 , and a plurality of sheets S are stacked by sheet bundle reception device  30 , thus, sheet bundle S 1  is formed. 
     The sheet bundle S 1  is conveyed to a prescribed position by the sheet bundle conveyance device  40 , and adhesive is coated on a spine of the sheet bundle S 1  by the adhesive coating device  50 . 
     Cover sheet S 2  supported by the cover supporting device  80  is bonded on a spine of the sheet bundle S 1  on which adhesive is coated, then, the cover sheet S 2  is folded along both edges of the spine of the sheet bundle S 1 , whereby, booklet S 3  is completed. 
     Next, each process of bookbinding will be described in detail. 
     Sheet S brought into the sheet conveyance device  10  is conveyed by plural conveyance rollers and by a conveyance path switching gate to any one of the sheet ejection device  20 , sheet bundle reception device  30 , and cover supporting device  80 . 
     When the bookbinding processing is not designated, sheet S ejected out of image forming apparatus A is ejected directly to a sheet ejection tray of the sheet ejection device  20  through setting of the conveyance path switching gate. 
       FIG. 3  is a diagram showing the structure of a bookbinding apparatus for illustrating forming of sheet bundle S 1  and processes thereafter. 
     The sheet bundle reception device  30  has therein sheet placing stand  35  arranged obliquely, sheet trailing edge positioning member  36  that is movable and aligning member  37  that conducts alignment in the sheet lateral direction. 
     A sheet ejected out of image forming apparatus A and sent by the aforesaid sheet conveyance device  10  is placed on the aforesaid sheet placing stand  35  successively, thus, sheet bundle S 1  composed of a prescribed number of sheets is formed. 
     After sheet bundle S 1  that is placed on sheet placing stand  35  of the sheet bundle reception device  30  has been aligned, it is grasped by grasping device  41 . After the sheet S 1  has been grasped by the grasping device  41 , sheet trailing edge positioning member  36  is moved by an unillustrated driving device to retreats toward the lower portion of the sheet placing stand  35 . 
     The grasping device  41  grasping the sheet bundle S 1  moves downward obliquely as shown by illustrated broken lines, and then, swings and stops at a prescribed position while holding the sheet bundle S 1  vertically so that spine Sa on which the adhesive coating processing is conducted on the sheet bundle S 1  may come to the lower side. 
     On the other hand, cover sheet S 2  stored in cover sheet stacking device  61  of the cover supply device  60  is separated and fed by sheet feeding device  62 , then, is pinched by conveyance rollers  63 ,  64  and  65  to be conveyed by conveyance rollers  81  and  82  of the cover supporting device  80 , and is stopped at a prescribed position. 
     When the cover sheet S 2  is longer than a necessary length in the case of conducting wrapping bookbinding processing for sheet bundle S 1 , the cover sheet S 2  is cut by cover cutting device  70  that is arranged on the right side in the illustration of conveyance roller  65 , so that an excessive portion may be removed in advance. 
       FIG. 4  is a diagram showing a structure of adhesive coating device  50 .  FIG. 5  is a perspective view showing adhesive coating device  50  and sheet bundle S 1  that is grasped by grasping device  41 , and  FIGS. 6(   a ) and  6 ( b ) are diagrams illustrating movements of adhesive coating device  50 . Meanwhile,  FIG. 6  ( a ) shows a side view, and  FIG. 6(   b ) shows a top view. 
     The adhesive coating device  50  has therein melting tank  53  representing a containing member that contains adhesive N, coating roller  51  representing a coating member, regulating members  503  and  504 , heaters H 1  and H 2 , adhesive temperature sensor TN and residual quantity sensor  506 . 
     The numeral  59  represents a replenishing device that replenishes solid adhesives PT, and it replenishes lump-shaped solid adhesives PT based on signals of residual quantity sensor  506  that detects an amount of adhesive in melting tank  53 . Meanwhile, heaters H 1  and H 2  are provided on the outer circumferential portion of the melting tank  53  and in coating roller  51 , and solid adhesive PT replenished to the melting tank  53  is heated up to the prescribed temperature to be melted to become adhesive N before coating. 
     Solid adhesive PT is replenished from replenishing device  59  depending on detection signals of residual quantity sensor  506 , to maintain the amount of adhesive N so that a surface of a liquid may be constant. 
     The numeral  503  represents a bar-shaped regulating member whose section is substantially a circle, and  504  represents a regulating member which is fixed on a plate-shaped supporting member  507  through screw cramp on both end portions outside the coating area. The melting tank  503  is set so as to be rotated around shaft  501 A from the state of standby shown with dotted lines to the state of coating shown with solid lines. 
     The regulating member  504  is a device to scrape off with primary scraping portion  504 A on the uppermost edge portion and with auxiliary scraping portion  504 C located to be slightly lower than the primary scraping portion  504 A, so that adhesive coated on a spine of sheet bundle S 1  by coating roller  51  may become the prescribed thickness. 
     A regulating member that regulates a thickness of an adhesive layer on coating roller  51  is represented by  504 D. 
     The regulating member  503  is a member that is arranged on the opposite side of coating roller  51  from the aforesaid regulating member  504  and regulates a coating thickness of adhesive. 
     The numeral  56  represents a shaping roller that regulates a thickness of adhesive layer NL formed on spine Sa. 
     The numeral  54  represents a movable body that supports melting tank  53 . The movable body  54  starts moving in the direction W 2  from an initial position (left end in  FIG. 6(   a )) on the back side of bookbinding apparatus B, then, moves along guide  55 , and is driven to be reversed in the direction W 3  to return to the initial position, after being stopped at the prescribed position on the front side of bookbinding apparatus B. 
     That is, coating of adhesive on spine Sa of sheet bundle S 1  held vertically is conducted in the manner wherein coating roller  51  that is dipped in adhesive in melting tank  53  and is driven by motor M 2  to rotate is caused to reciprocate on spine Sa of a sheet bundle, and an amount of coating for adhesive N is regulated mainly by regulating member  503  in the case of the outward movement (direction W 2 ), and is regulated mainly by regulating member  504  and by shaping roller  56  in the case of the homeward movement (direction W 3 ). 
     Solenoid SOL 1  moves coating device  50  vertically, and solenoid SOL 2  rotates melting tank  53  between a position of solid lines and a position of dotted lines in  FIG. 4 . 
     In the case of coating on the outward trip, melting tank  53  is set to the state of solid lines by “ON” of solenoid SOL 2 , and regulating member  503  regulates a coating thickness. 
     In the case of coating on the homeward trip, melting tank  53  is set to the state of dotted lines by “OFF” of solenoid SOL 2 , and regulating member  504  and shaping roller  56  regulate a coating thickness. 
       FIG. 7  is a conceptual diagram showing positions of sheet bundle conveyance device  40  and of cover supporting device  80 , in the case of conducting gluing processing between sheet bundle S 1  and cover sheet S 2 . 
     After completion of coating adhesive on sheet bundle S 1 , elevating device  86  moves movable casing  84  to the elevated position representing a prescribed position with an unillustrated driving device. At this elevated position, a central portion of cover sheet S 2  placed on pressure member  83  is brought into pressure contact with a surface of sheet bundle S 1  coated with adhesive, to be bonded thereon. 
       FIGS. 8(   a )- 8 ( d ) are cross-sectional views of cover supporting device  80  and sheet bundle S 1  showing a folding process for cover sheet S 2 , and  FIG. 8(   a ) shows a moment to start folding a cover sheet,  FIG. 8(   b ) shows an intermediate moment for cover sheet folding,  FIG. 8(   c ) shows a moment of termination of cover sheet folding and  FIG. 8(   d ) shows a moment of releasing pressurization for cover folding. 
     After cover sheet S 2  is bonded on spine Sa of sheet bundle S 1  on which adhesive N is coated, paired folding members  88  are driven by an unillustrated driving device, in the course of an ascending state of cover supporting device  80  shown in  FIG. 7 . Then, grasping device  41  that is grasping the sheet bundle S 1  descends. Owing to descending of the sheet bundle S 1 , cover sheet S 2  descends while being supported by the paired folding members  88 , and is bent on side edge portions of adhesive-coated surface of the sheet bundle S 1 . 
     After that, the paired folding members  88  move toward the adhesive-coated surface side of sheet bundle S 1  in the horizontal direction to shape both sides of the sheet bundle S 1  by pressing them, and form booklet S 3 . 
     The booklet  3  which has been ejected by ejection belt  87  (see  FIG. 3 ) is placed on conveyance belt  91  of booklet storing device C shown in  FIG. 1 , which is capable of ascending and descending, and is ejected successively by rotation of the conveyance belt  91  to be stacked on sheet ejection stand  92  to be stored. 
     &lt;Coating Thickness Control&gt; 
     Adjustment of a coating thickness of adhesive formed on spine Sa of sheet bundle S 1  will be described. 
     As described above, coating of adhesive is conducted by one reciprocation of coating device  50 . 
     A thickness of an adhesive layer formed by one reciprocation of coating device  50  is determined mainly by coating process of a homeward trip. 
     Coating operations in a homeward trip of the coating device  50  will be described as follows, referring to  FIG. 9 . 
     When the coating device  50  moves in the direction W 3 , coating roller  51  rotates in the counterclockwise direction W 1 , to apply adhesive N on spine Sa of booklet bundle P. 
     That is, when the coating device  50  moves in the direction W 3 , a circumferential surface of the coating roller  51  rotates in the counter direction that increases relative velocity caused between booklet S 1  and the circumferential surface, and coating is carried out. 
     Adhesive N thus applied is shaped by regulating member  504  to be of a thickness of t 1  in  FIG. 9 , and then, is shaped by shaping roller  56  to be of a thickness of t 2 . 
     Since a speed of the coating device  50  to move in the direction W 3  and a rotating speed of the coating roller  51  are constant, a thickness of coated adhesive layer NL is determined by clearances between spine Sa and each of the coating roller  51 , regulating member  504  and the shaping roller  56 . 
     In the illustrated coating device  50 , heights of the coating roller  51 , the regulating member  504  and of the shaping roller  56  are adjusted by solenoid SOL 1  (see  FIG. 4 ), and thereby, a thickness of adhesive layer NL is adjusted. 
     In other words, when the coating roller  51 , the regulating member  504  and the shaping roller  56  are set respectively at high positions, so that a distance between each of these items and spine Sa is made to be narrow, thin adhesive layer NL is formed, and when these items are set respectively at low positions, so that a distance between each of them and spine Sa is made to be broad, thick adhesive layer NL is formed. 
     A thickness of adhesive layer NL is adjusted in the aforesaid way based on a thickness of booklet bundle S 1 . 
     As shown in  FIG. 9 , the coating thickness means thickness t 2  of adhesive layer NL that is formed on sheet bundle S 1  after coating process, and a thickness of the adhesive layer after drying is determined by the value of the coating thickness t 2 . 
     That is, a thickness of adhesive layer NL is controlled by making thickness t 2  of adhesive layer NL thick when booklet bundle S 1  is thick, and by making thickness t 2  of adhesive layer NL thin when booklet bundle S 1  is thin. 
     In the example described above, coating thickness t 2  is determined mainly by a distance between a circumferential surface of shaping roller  56  and spine Sa, and control of the coating thickness is determined by a direction of rotation and a rotation speed of coating roller  51 , and by a movement speed of adhesive coating device  50 . 
     By the control of a coating thickness of this kind, a phenomenon that is called a side adhesive wherein coated adhesive spreads up to a sheet surface of a booklet from spine Sa can be prevented in a thin booklet bookbinding process, and the strength necessary for a thick booklet can be secured. 
     In the typical example of the control of this kind for a coating thickness of adhesive, information on a booklet thickness is distinguished by using a prescribed threshold value, and when the thickness is not smaller than the threshold value, thick coating is conducted, and when the thickness is smaller than the threshold value, thin coating is conducted. 
     When the coating thickness control of this kind is conducted, unevenness is caused on the finish of the booklet as described above, and quality of the booklet is lowered. 
     In the invention, the aforesaid problems have been solved by conducting coating thickness control by adding booklet information including at least information on the number of sheets constituting sheet bundle S 1  to information on the thickness of sheet bundle S 1 , while keeping the adjustment of a coating thickness of adhesive layer NL based on a thickness of sheet bundle S 1  as a fundamental method. 
       FIG. 10  is a block diagram of a control system that conducts control of coating thickness and conducts control of cutting of a cover sheet. 
     Control device CR controls a coating thickness by controlling solenoid SOL 1  that controls a position of coating device  50 , based on information from sheet bundle thickness detector DT constituting a thickness information generating device, and corrects the coating thickness control based on information on sheet bundle thickness detector DT based on information from booklet information generating device SG. 
     The sheet bundle thickness detector is one to detect a distance between paired grasping devices  41  (see  FIG. 3 ). 
     Further, booklet information generating device SG is a device to generate information on at least the number of sheets constituting a sheet bundle, and it includes a communication device that conducts communication with operation display device  9  (see  FIG. 1 ) and with outer equipment. 
     In addition to the information on the number of sheets, booklet information generated by the booklet information generating device SG can include at least one of information on a sheet thickness, information on a sheet size and information on a sheet type. 
     Control device CR controls an amount of feeding for cover sheet S 2  to be fed to cutter  70 , based on information from the booklet information generating device SG and on information from the sheet bundle thickness detector DT. 
     Since a cover sheet is cut to the length of cover sheet S 2  according to a sheet size and a sheet bundle thickness, by the control of an amount of feeding of cover sheet S 2  of this kind, a cover sheet suitable for a sheet size and various sheet bundle thicknesses is prepared, and is joined with a bundle for a booklet. 
       FIG. 11  is a flow chart of a coating thickness control in an example of the embodiment of the invention. 
     In  FIG. 11 , S 11 -S 1   n  represent the number of sheets constituting the first sheet bundle-n th  sheet bundle. 
     In step ST 1 , the number of sheets S 11  of sheets constituting the first sheet bundle is counted. This number of sheets is a counted number of sheets S accumulated in sheet storing device  30  (see  FIG. 1 ). 
     In step ST 2 , the number of sheets S 11  thus counted is set as an initial value. 
     In step ST 3 , a thickness of sheet bundle is judged whether the number of sheets S 11  thus counted is smaller than the threshold value (for example, 7 mm) or not. Information on a thickness is obtained by measuring a distance between paired grasping devices  41  (see  FIG. 5 ), and judgment in step T 3  is conducted by reading this information. 
     When thickness T is judged to be threshold value T 0  or more in step ST 3 , thick coating is conducted in step ST 4 . Specifically, coating is conducted under the set situation wherein coating roller  51 , shaping roller  56  and regulating member  504  in  FIG. 9  are positioned to be low, and a distance between spine Sa of sheet bundle S 1  and each of the aforesaid items is broad. 
     After coating of adhesive, the number of sheets S 1   n  for the succeeding sheet bundle is counted. 
     When the counted number of sheets is not changed from the initial value, namely from the number of sheets S 11  of a sheet bundle (Yes in ST 7 ), the process returns to step ST 4 , and thick coating is conducted. 
     When steps ST 4 -ST 7  are repeated and the job is terminated (Yes in ST 5 ), the process flow is terminated. 
     When the number of sheets S 1   n  of sheet S constituting a bundle of sheets is judged to be different from the initial value in step ST 7  (No in step  7 ), the counted number of sheets is set as an initial value (ST 2 ). 
     When a thickness of the bundle of sheets is judged to be thinner than threshold value T 0  in step ST 3  (No in step  3 ), thin coating is conducted in step ST 8 . 
     Specifically, thin coating is conducted under the condition wherein coating roller  51 , shaping roller  56  and regulating member  504  in  FIG. 9  are set to be high, and a distance between each of these items and spine Sa is made to be narrow. 
     In step ST 9 , existence of a job is judged, and when it is a job end (Yes in ST 9 ), the process flow is terminated, while, when it is not a job end, the number of sheets S 1   n ′ of sheets S constituting following sheet bundle is counted in step ST 10 . 
     When the counted number of sheets is not changed from an initial value, the process returns to step ST 8  to conduct thin coating, while, when the number of sheets is changed, the process returns to step ST 2  to set the counted value in step ST 10  as an initial value. 
     As illustrated in  FIG. 11  and as described above, it is a basic method to select one of thick coating and thin coating according to a thickness of a sheet bundle. However, there is conducted coating control to coat while keeping a coating mode having been set before, when taking in information on the number of sheets constituting a bundle of sheets that is booklet information and there is no change in the booklet information. 
     Though the coating mode having been set before is kept when the counted number of sheets is not changed from the initial value in the example, the number does not always need to be the same, and it is naturally possible to keep the coating mode if a difference of the number of sheets is within a prescribed number of sheets. 
     Owing to this, it is prevented that a coating thickness is varied by fluctuation of a reading value of a thickness of a sheet bundle and that unevenness of an outer shape is caused between booklets. 
     Incidentally, it is possible to cause booklet information to include at least one of a thickness of each sheet (sheet thickness), a sheet size and a sheet type in addition to the number of sheets constituting a booklet. 
     Further, though the example of control in  FIG. 11  is an example wherein two types of coating thicknesses are used for coating by using one threshold value, it is possible to conduct coating thickness control shown in  FIG. 11  wherein booklet information is taken into consideration, even in the case of conducting coating three or more types of coating thicknesses by using plural thresholds.