Abstract:
An image forming apparatus includes: an image forming section that forms a toner image on a sheet; a fixing section that fixes the toner image on the sheet; a sheet conveyance path that branches into a first sheet conveyance path and a second sheet conveyance path downstream of the fixing section; a blowing section that guides the sheet to the first sheet conveyance path or to the second sheet conveyance path by blowing air to the sheet; and a controller that controls the blowing air of the blowing section.

Description:
[0001]    This application is based on Japanese Patent Application No. 2008-130550 filed on May 19, 2008, which is incorporated hereinto by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an advancing direction switching section for a sheet that is in a sheet conveyance path of an image forming apparatus. 
         [0003]    In general, an image forming apparatus of an electrophotographic type transfers a toner image visualized through toner development onto a sheet, and fixes the toner image on a sheet by pressing and heating the sheet onto which the toner image has been transferred with a fixing section. 
         [0004]    The aforesaid sheet which has been subjected to fixing processing by the aforesaid fixing section is guided to the first sheet conveyance path or to the second sheet conveyance path, by a sheet conveyance path switching section that switches advancing directions for a sheet. 
         [0005]    The aforesaid first sheet conveyance path is, for example, a sheet conveyance path through which the aforesaid sheet is sent to a sheet ejection tray of the image forming apparatus, or to a sheet finisher that is connected to the downstream side, while, the aforesaid second sheet conveyance path is, for example, a sheet conveyance path through which the aforesaid sheet is sent to a sheet reversing device, or to a sheet re-feeding device that is for forming an image on the reverse side of the aforesaid sheet. 
         [0006]    Many of the aforesaid sheet conveyance path switching sections are constructed so that the aforesaid sheet may be guided to the prescribed sheet conveyance path by moving the sheet guide member on which a leading edge portion of the sheet rubs, and therefore by regulating the advancing direction of the sheet (for example, see Unexamined Japanese Patent Application Publication No. 2006-330250). 
         [0007]    The sheet conveyance path switching section of this kind can be realized in a simple structure, and it is characterized to be low in cost, but it gives strong stress to the sheet, because the sheet immediately after fixing processing comes in pressure contact with a guide member to be bent. 
         [0008]    Further, there are sometimes caused problems wherein toner and wax on the sheet surface stick to the aforesaid sheet guide member, and the sticking toner and wax stick again to the sheet because an image surface of the sheet heated by fixing processing rubs against the sheet guide member. 
       SUMMARY OF THE INVENTION 
       [0009]    The invention has been achieved in view of the situations mentioned above, and its object is to realize an image forming apparatus having a sheet conveyance path that branches into the first sheet conveyance path and the second sheet conveyance path at the downstream side of a fixing unit, wherein there is provided an air sending section that switches the sheet conveyance path for the sheet to the first conveyance path or to the second conveyance path, by blowing air against the sheet. 
         [0010]    An aspect for attaining the aforesaid object is as follows. 
         [0011]    An image forming apparatus characterized in that an image forming section that forms a toner image on a sheet, a fixing section that fixes the toner image on the sheet, a sheet conveyance path that branches into the first sheet conveyance path and the second sheet conveyance path at the downstream side of the aforesaid fixing section, a blowing section that guides the aforesaid sheet to the first sheet conveyance path or to the second sheet conveyance path by blowing air to the sheet and a controller that controls blowing of the blowing section, are provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a conceptual diagram of a conventional image forming apparatus. 
           [0013]      FIG. 2  is a conceptual diagram of an image forming apparatus in the present embodiment. 
           [0014]      FIG. 3  is a block diagram showing relationship for controlling an image forming apparatus. 
           [0015]      FIG. 4  is a diagram illustrating relationship of arrangement for a sheet conveyance path and a blowing member. 
           [0016]      FIG. 5  is a block diagram illustrating the structure of the blowing section. 
           [0017]    Each of  FIGS. 6(   a )- 6 ( d ) shows an example of an air amount changing section. 
           [0018]      FIG. 7  is a flow chart showing a flow of blowing control. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    An example of the embodiment of the invention will be explained as follows based on drawings. Incidentally, the invention is not limited to the present example. 
         [0020]      FIG. 1  is a conceptual diagram of a conventional color image forming apparatus G. 
         [0021]    The color image forming apparatus G exemplified in the drawing is one that is called a tandem type color image forming apparatus wherein a plurality of photoconductors  31 Y,  31 M,  31 C and  31 K are arranged in tandem to face a single intermediate transfer belt  41 , and a full-color image is formed. 
         [0022]    This color image forming apparatus G is equipped, on its upper portion, with automatic document feeder ADF. 
         [0023]    Documents D placed on document table  103  of the automatic document feeder ADF are separated to be a single sheet to be sent out to a document conveyance path, and is conveyed by conveyance drum  108 . 
         [0024]    An image of the documents D during conveyance is read by document reading section  1  at document image reading position RP. The document D which has been finished in terms of image reading is ejected to document ejection tray  107  by a plurality of conveyance guides and by document ejection roller  105 . 
         [0025]    Image forming apparatus G is composed of document reading section  1 , exposure sections  2 Y,  2 M,  2 C and  2 K, image forming sections  3 Y,  3 M,  3 C and  3 K, intermediate transfer section  4 , fixing section  5 , reversing sheet ejection section  6 , sheet re-feeding section  7 , sheet feeding section  8  and control section C which are housed in a single casing. 
         [0026]    The document reading section  1  illuminates a document image with lamp L at document image reading position RP, and guides its reflected light with first mirror unit  11 , second mirror units  12 , and lens  13 , to cause the reflected light to form an image on a light-receiving surface of charge coupled device image sensor CCD. 
         [0027]    Image signals obtained through photoelectric conversion by charge coupled device image sensor CCD undergo processes including A/D conversion by image reading control section  14 , shading correction, and compression, which are stored in a memory of control section C as image data. 
         [0028]    The aforesaid image data stored in the memory undergo appropriate image processing based on conditions established by a user, and output image data are created. 
         [0029]    Each of exposure sections  2 Y,  2 M,  2 C and  2 K is composed of a laser light source, a polygon mirror and a plurality of lenses, and it creates a laser beam. 
         [0030]    Each of exposure sections  2 Y,  2 M,  2 C and  2 K conducts scanning exposure by a laser beam on the surface of each of photoconductors  31 Y,  31 M,  31 C and  31 K representing constituent elements for image forming sections  3 Y,  3 M,  3 C and  3 K, corresponding to output information outputted based on the aforesaid output image data. 
         [0031]    A latent image is formed on each of the photoconductors  31 Y,  31 M,  31 C and  31 K through the aforesaid scanning exposure by a laser beam. 
         [0032]    Image forming section  3 Y is composed of photoconductor  31 Y, and of main charging section  32 Y, developing section  33 Y, first transfer roller  34 Y and cleaning section  35 Y which are arranged around the photoconductor  31 Y. The same is equally true of the photoconductors  31 M,  31 C and  31 K. 
         [0033]    Latent images on the photoconductors  31 Y,  31 M,  31 C and  31 K are developed by respective developing sections  33 Y,  33 M,  33 C and  33 K which correspond to the aforesaid photoconductors, whereby, each toner image is formed on each photoconductor. 
         [0034]    The aforesaid toner images formed respectively on photoconductors  31 Y,  31 M,  31 C and  31 K are transferred one after another at prescribed positions on intermediate transfer belt  41  representing an intermediate transfer body, by first transfer rollers  34 Y,  34 M,  34 C and  34 K of intermediate transfer device  4 . 
         [0035]    Toner remaining on a surface of the photoconductor from which a toner image has been transferred is removed by each of cleaning sections  35 Y,  35 M,  35 C and  35 K. 
         [0036]    On the other hand, the aforesaid toner image transferred onto the aforesaid intermediate transfer belt  41  is conveyed by second transfer roller  42  from each of trays PG 1 , PG 2  and PG 3  of sheet feeding section  8 , or from sheet feeding device S 1 , and is transferred onto sheet P that is fed out after its timing is controlled by sheet feeding roller  81 . 
         [0037]    A surface of the intermediate transfer belt  41  on which the transfer of a toner image onto sheet P has been finished is cleaned by belt cleaning section  43 , to be ready for the succeeding image transfer. 
         [0038]    On the other hand, sheet P carrying a toner image is conveyed to fixing section  5  where the toner image is fixed on the sheet P when it is pressed and heated. 
         [0039]    Sheet P that has been finished in terms of fixing processing by fixing section  5  is guided by sheet conveyance path switching section  6  in terms of its advance path, and is ejected to sheet ejection tray  61 . 
         [0040]    When ejecting sheet P after reversing inside out, the sheet P is guided downward temporarily by sheet ejection guide  62 , then, the sheet P is reversed after causing sheet ejection reversing roller  63  to interpose a trailing edge of sheet P, and the sheet is guided to sheet ejection roller  64  by sheet ejection guide  62  to be ejected. 
         [0041]    Incidentally, when forming an image also on the reverse of sheet P, sheet P that is finished in terms of image fixing on the obverse is conveyed to sheet re-feeding section  7  located below by sheet guide member  62 , and the sheet P is reversed by sending it reversely after causing re-feed reversing roller  71  to interpose a trailing edge, thus, the sheet P is fed out to sheet re-feeding conveyance path  72  to be ready for image forming on the reverse. 
         [0042]      FIG. 2  is a conceptual diagram of image forming apparatus G 1  in the present embodiment. 
         [0043]    Though the image forming apparatus G 1  is different from color image forming apparatus G in terms of a structure of sheet conveyance switching section  6  at downstream side of a fixing section, other points are the same. Thus, the overall explanation will be omitted. 
         [0044]      FIG. 3  is a block diagram showing relationship for controlling image forming apparatus G 1 . 
         [0045]    Control section C 1  of image forming apparatus G 1  is a computer system having therein CPU, memory M 1 , an operation unit, I/O port, an interface for communication and drive circuit. 
         [0046]    The control by the control section C 1  is carried out by performing the prescribed programs stored in memory M 1 . 
         [0047]    Further, the control section C 1  is connected to a network to be capable of exchanging information with other information exchange equipment. 
         [0048]    In the present drawing, meanwhile, descriptions of blocks which are not related directly to the explanation of the present embodiment are omitted. 
         [0049]      FIG. 4  is a diagram illustrating relationship of arrangement for sheet conveyance path  100  and blowing members  210  and  220 . 
         [0050]    The sheet conveyance path  100  is one arranged at the downstream side of fixing section  5 , and it is a sheet conveyance path through which sheet P that has been finished in terms of fixing processing and has been detected by sheet detection sensor SP in terms of its leading edge is guided to the first sheet conveyance path  101  or to the second sheet conveyance path  102 . 
         [0051]    At a point where the aforesaid sheet conveyance path  100  is branched into the first sheet conveyance path  101  and to the second sheet conveyance path  102 , there are arranged first blowing member  210  and second blowing member  220  both representing a blowing nozzle that blows air against sheet P, in a way to face each other. 
         [0052]    Meanwhile, in an example shown in  FIG. 2 , a conveyance path for conveying sheet P toward sheet ejection tray  61  corresponds to the first sheet conveyance path, and a conveyance path for conveying sheet P toward sheet ejection reversing roller (also referred to as sheet reversing section)  63  or toward sheet re-feeding section  7  corresponds to the second sheet conveyance path. 
         [0053]    Furthers with respect to a direction of the blowing nozzle, it is not perpendicular to a plane of sheet P, but it is oblique so that a tip of the nozzle may be in the advancing direction of sheet P as shown in the drawing. By providing the inclination of this kind, air can flow in the advancing direction of sheet P, and conveyance of the sheet is stabilized. 
         [0054]    Further, the first blowing member and the second blowing member are arranged so that blown air blowing out of the first blowing member and the second blowing member may advance in the direction toward the leading edge of the sheet after hitting the surface of the advancing sheet. 
         [0055]      FIG. 5  is a block diagram illustrating the structure of blowing section  200 . 
         [0056]    The blowing section  200  is composed of first blowing member  210 , air valve  211 , second blowing member  220 , air valve  221 , air tank  230 , air pump  240  and air duct  260 . 
         [0057]    The air pump  240  sends air so that air pressure in the air tank  230  may keep prescribed pressure. 
         [0058]    Air in the aforesaid air tank is sent to the first blowing member  210  or to the second blowing member  220 , when air valve  211  or air valve  212  which is opened or closed by instruction signals  219  or  229  of control section C 1  is opened. Further, air sending to the first blowing member  210  or to the second blowing member  220  is intercepted, when the air valve  211  or the air valve  212  is closed. 
         [0059]    Owing to the structure mentioned above, timing of the start of air blowing from the first blowing member  210  or the second blowing member  220 , or timing of interception, is controlled by control section C 1 . 
         [0060]    On apical portions respectively of the first blowing member  210  and the second blowing member  220 , there are respectively provided the first air amount changing section  251  whose position is changed by instruction signal  218  of control section C 1  and the second air amount changing section  252  whose position is changed by instruction signal  228  of control section C 1 . 
         [0061]    Namely, an amount of air blowing against sheet P from forefronts of the first blowing member  210  and the second blowing member  220  per unit time is controlled when the control section C 1  controls the first air amount changing section  251  and the second air amount changing section  252 . 
         [0062]    Each of  FIGS. 6(   a )- 6 ( d ) shows an example of an air amount changing section. Meanwhile, the structure of the first air amount changing section  251  is the same as that of the second air amount changing section  252 . 
         [0063]      FIG. 6(   a ) is a conceptual diagram of the first blowing member  210 , and air that is conveyed through air duct  260  blows out in the direction of arrow “f” from slit-shaped air blowing outlet  259  of the first blowing member  210 . 
         [0064]    The first air amount changing section  251  is provided on the blowing outlet of the first blowing member  210 . Each of  FIGS. 6(   b ),  6 ( c ) and  6 ( d ) is an example of the first are amount changing section  251 . 
         [0065]      FIG. 6(   b ) is an example wherein an amount of air that hits sheet P is changed when member  255  having small holes formed in a staggered pattern is moved to a blowing outlet of the first blowing member  210 . 
         [0066]    Further,  FIG. 6(   c ) is an example wherein an amount of air that hits sheet P is changed when indented member  256  is moved at a blowing outlet of the first blowing member  210 . 
         [0067]    Further,  FIG. 6(   d ) is an example wherein an amount of air that hits sheet P is changed when member  257  that is opened and closed symmetrically is caused to open and close at a blowing outlet of the first blowing member  210 . 
         [0068]    Each of the aforesaid members  255 ,  256  and  257  is called an opening area adjusting member. 
         [0069]      FIG. 7  is a flow chart showing a flow of blowing control. 
         [0070]    Control of blowing is one wherein sheet P advancing to sheet conveyance path  100  is guided to the first sheet conveyance path  101  or to the second sheet conveyance path  102  by spraying air against sheet P following specifications of a job established in advance, and sheet P that advances further receives blowing to cool an image plane. 
         [0071]    After the leading edge of sheet P is detected by sheet detection sensor SP (step S 1 : Y), sheet conveyance path selection information that is determined by specifications of the job established on image forming apparatus G 1  is acquired. Further, sheet leading edge position information that is a distance by which the leading edge of sheet P advances from a position of the sheet detection sensor SP is calculated one after another from a conveyance speed of sheet P (step S 2 ). 
         [0072]    After it becomes clear that the leading edge of sheet P has arrived at the position established in advance by the aforesaid calculated sheet leading edge position information (step S 3 : Y), the sheet P is judged whether it is sheet P to be sent to the first sheet conveyance path  101  or not, referring to the aforesaid acquired sheet conveyance path selection information (step S 4 ). 
         [0073]    If the sheet P is one to be sent to the first sheet conveyance path, second air valve  212  is opened so that air may blow out of second blowing member  220  positioned below the sheet P (step S 5 ). An amount of air blowing out per unit time is determined by the second air amount changing section  252 . 
         [0074]    When a leading edge portion of sheet P is guided to the first sheet conveyance path  101  by air blowing out of the second blowing member  220  and the leading edge of sheet P arrives at an air amount changing position established in advance (step  6 : Y), an amount of air blowing out of the second blowing member  220  is reduced (step S 7 ). 
         [0075]    A change of an amount of air blowing out of the second blowing member  220  of this kind reduces problems that contact between an image surface of sheet P and a sheet guide member of the first sheet conveyance path is weakened, toner and wax on the sheet surface stick to the aforesaid sheet guide member. 
         [0076]    Meanwhile, in the example stated above, a leading edge portion of sheet P is guided by air blowing out of the second blowing member  220  to the first sheet conveyance path  101 , for easy understanding of the explanation. However, it is preferable to construct so that air may blow out of both the first blowing member  210  and the second blowing member  220 , and a leading edge portion of sheet P may be guided to the first sheet conveyance path  101  by the difference between an amount of air from the first blowing member  210  and that of air from the second blowing member  220 . 
         [0077]    By constituting as stated above so that both sides of sheet P are constantly hit by air, air flows constantly on an image surface of sheet P, thus, a toner image heated in fixing device  5  is cooled rapidly, rubbing between sheet P and a sheet guide member is reduced, and a problem that toner and wax on the surface of the sheet stick to the sheet guide member is further reduced. 
         [0078]    After the trailing edge of sheet P is detected by sheet detection sensor SP (step S 8 : Y), or after the passage of prescribed time since the detection, an air valve that has been opened is closed (step  12 ) to finish the routine. 
         [0079]    On the other hand, in step S 4 , when sending sheet P to second sheet conveyance path  102  (step S 4 : N), the first air valve  211  is opened (step S 9 ) so that air may blow out of the first blowing member  210  that is located above the sheet P. Meanwhile, an amount of air emitted per unit of time is determined by the first air amount changing section  251 . 
         [0080]    When a leading edge portion of sheet P is guided to the second sheet conveyance path  102  by air blowing out of the first blowing member  210  and the leading edge arrives at a position for changing an amount of air established in advance (step S 10 : Y), an amount of air blowing out of the first blowing member  210  is reduced (step S 11 ). 
         [0081]    In the example stated above again, a leading edge portion of sheet P is guided by air blowing out of the second blowing member  210  to the second sheet conveyance path  102 , for easy understanding of the explanation. However, it is preferable to construct so that air may blow out of both the first blowing member  210  and the second blowing member  220 , and a leading edge portion of sheet P is guided to the second sheet conveyance path  102  by the difference between an amount of air from the first blowing member  210  and that of air from the second blowing member  220 . 
         [0082]    By constituting, as stated earlier, so that both sides of sheet P may be constantly hit by air, air flows constantly on an image surface of sheet P, thus, a toner image heated in fixing device  5  and sheet P are cooled rapidly, and rubbing between sheet P and a sheet guide member is reduced. 
         [0083]    As a result, a problem that toner and wax on a surface of the sheet stick to the sheet guide member, and a problem of occurrence of curls which are caused when strong stress is applied on overheated sheet P, are reduced. 
         [0084]    After the trailing edge of sheet P is detected by sheet detection sensor SP (step S 8 : Y), or after the passage of prescribed time since the detection, an air valve that has been opened is closed (step  12 ) to finish the routine. 
         [0085]    In the case of switching of sheet conveyance paths in the present embodiment in the image forming apparatus having a sheet conveyance path that is branched into the first sheet conveyance path and the second sheet conveyance path, at the downstream side of the fixing device, occurrence of curls of sheets can be suppressed, because strong stress is not applied on the sheet immediately after fixing processing, which is different from sheet conveyance path switching in which a sheet conveyance path is switched by a sheet guide member. 
         [0086]    Further, it is possible to prevent a problem that toner and wax stick to the sheet guide member and to stick again to the sheet, because an image surface of the sheet heated by fixing processing does not rub strongly against the aforesaid sheet guide member, and is further cooled by air.