Abstract:
An air blowing unit is arranged so as to blow air toward a side edge of a sheet discharged from a discharging port. Alternatively, the air is blew from below the discharged sheet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a sheet stacking device that can neatly stack sheets that are discharged by a sheet delivery device (including a printer).  
           [0002]    When sheets, thick or thin, are smooth and flat, due to the friction produced between the sheets a stacker for a sheet delivery device can not stack them neatly. And if the stacking is performed as a continuous process, paper jamming tends to occur and the sheet delivery device would be damaged. Thus, to prevent damage, the sheet delivery device must be halted.  
           [0003]    To avoid paper jamming, the sheet stacking device can be tilted downward, so that sheets are gravity stacked. However, in this case folding at the distal end of the sheets, or stacking failures due to the curling of the sheets may occur.  
           [0004]    When further improvements are provided, the sheet delivery device becomes larger and more complicated, which is not preferable.  
           [0005]    The reference documents concerning sheet material are Japanese Patent Publication Nos. 4-296594A, 4-327982A and 4-327983A, which were proposed by the present applicant. And the reference document concerning the sheet delivery device that employs the above described sheets is Japanese Patent Publication No. 8-132654A, which was also proposed by the present applicant.  
         SUMMARY OF THE INVENTION  
         [0006]    It is one objective of the present invention to provide a small and less expensive stacking device that can stack sheets neatly at a predetermined stacking location, regardless of the shape and the thickness of the sheets, and the material of which they are composed.  
           [0007]    In order to achieve the above object, there is provided a sheet stacking device comprising:  
           [0008]    a sheet discharging port from which a sheet is discharged;  
           [0009]    an air blowing unit for blowing air toward the sheet discharged from the sheet discharging port; and  
           [0010]    a stacker on which the blew sheet is stacked.  
           [0011]    The air blowing unit may be arranged so as to blow the air toward a side edge of the discharged sheet.  
           [0012]    Here, the air blowing unit may be arranged at least one of downstream and along the sheet discharging direction such that the air is blew toward the center portion of the discharged sheet in the widthwise direction thereof.  
           [0013]    Preferably, the air blowing unit blows the air intermittently.  
           [0014]    Here, a cycle of the intermittent blowing is determined in accordance with the length of the sheet having been discharged.  
           [0015]    Preferably, the air blowing unit blows the air every time 5 to 20 cm of the sheet has been discharged.  
           [0016]    Alternatively, the air blowing unit may be arranged so as to blow the air from below the discharged sheet.  
           [0017]    Preferably, the air blowing unit is arranged in the vicinity of the sheet discharging port.  
           [0018]    Preferably, the air blowing unit blows the air intermittently.  
           [0019]    The sheet stacking device may further comprises a sensor for detecting that the sheet has been discharged from the discharging port. Here, the air blowing unit starts to blow the air upon the detection of the sensor and continues blowing the air until the sheet is stacked on the stacker.  
           [0020]    Preferably, the stacker is arranged so as to support one corner portion of the blew sheet independent from the size of the sheet.  
           [0021]    According to the present invention, there is also provided a method of stacking sheets discharged from a sheet discharging port, comprising the steps of:  
           [0022]    blowing air toward the discharged sheet; and  
           [0023]    placing the blew sheet at a predetermined position.  
           [0024]    The air may be blew toward a side edge of the discharged sheet.  
           [0025]    Here, the air is blew from at least one of a downstream area and a side area of the sheet discharging direction such that the air is blew toward the center portion of the discharged sheet in the widthwise direction thereof.  
           [0026]    Preferably, the air is blew intermittently.  
           [0027]    Here, a cycle of the intermittent blowing is determined in accordance with the length of the sheet having been discharged.  
           [0028]    Preferably, the air is blew every time 5 to 20 cm of the sheet has been discharged.  
           [0029]    Alternatively, the air may be blew from below the discharged sheet.  
           [0030]    Preferably, the air is blew from the vicinity of the discharging port.  
           [0031]    Preferably, the air is blew intermittently.  
           [0032]    The sheet stacking method may further comprises the steps of detecting that the sheet has been discharged from the discharging port. The air blowing is started upon the detection of the sensor and continued until the placing step is conducted.  
           [0033]    Preferably, one corner portion of the blew sheet is supported independent from the size of the sheet.  
           [0034]    According to the above configuration, air enters a gap between individual stacked sheets, and the contact area between the sheets is reduced. As a result, the sheets can be stacked neatly at a predetermined position, regardless of the shape and the thickness of the sheets, and the material of which they are composed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    In the accompanying drawings:  
         [0036]    [0036]FIGS. 1A to  1 C are schematic diagrams illustrating a sheet stacking device according to a first embodiment of the present invention;  
         [0037]    [0037]FIGS. 2A to  2 C are plan views for explaining an experiment for finding an appropriate location of an air ejection port; and  
         [0038]    [0038]FIGS. 3A to  3 C are schematic diagrams illustrating a sheet stacking device according to a second embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]    [0039]FIGS. 1A to  1 C are schematic diagrams illustrating a sheet stacking device according to the first embodiment of the present invention. FIG. 1A is a side view of the sheet stacking device, FIG. 1B is a front view thereof and FIG. 1C is a plan view thereof.  
         [0040]    A sheet delivery unit  1  comprises: discharging rollers  2 , for the external discharge of a sheet by the sheet delivery unit  1 ; an air ejection port  3 , which is the feature of the present invention; a stopper  4 ; and a slide face  6 , along which a sheet  9  that is being discharged slides. The slide face  6  also serves as the top of a casing body for a printer that includes the sheet delivery unit  1 . In the first embodiment, the sheet stacking device is constituted by the air ejection port  3  from ejected air is directed toward the side of sheet, the stopper  4 , a fan (not shown) and the slide face  6 .  
         [0041]    An explanation will now be given for the processing performed for the first embodiment for blowing air from the side of the sheet that is discharged.  
         [0042]    The sheet  9 , while sandwiched between the upper and lower discharging rollers  2 , is externally discharged by the sheet delivery unit  1 , and is transported along the slide face  6  in the direction indicted by a white arrow shown in FIGS. 1B and 1C. At this time, when air from the air ejection port  3  is blew against the side of the sheet  9 , the force exerted in the direction indicated by arrows is applied to the sheet  9 , and the lower edge on the right side of the sheet  9  is held at the stopper  4 .  
         [0043]    Thereafter, the same process is performed for succeeding sheets  9 , until finally, all the sheets  9  are held and stacked at the stopper  4 . Since air from the air ejection port  3  enters gaps between the individual sheets and forms air layers, the contact area for the sheets is reduced, and a preferable stacked state is provided.  
         [0044]    According to this embodiment, the sheets  9  can be neatly stacked at the predetermined stopper  4 , the contact area for the sheets is reduced due to the air layer formed in the gaps between the sheets, and a preferable sheet stacked state is provided.  
         [0045]    In addition, since the lower edge on the right side of the sheet  9  is held at the stopper  4  by ejected air, this device can be applied for any type of sheet  9 , regardless of the sheet size.  
         [0046]    [0046]FIGS. 2A to  2 C are plan views of a sheet stacking device for which an experiment was conducted to find an appropriate location for the air ejection port  3 .  
         [0047]    In the sheet stacking device in FIG. 2A, the air ejection port  3  is provided in an area A 1  that is located along the sheet delivery direction, or that is downstream in the sheet delivery direction on the side whereat the stopper  4  is not provided, so that the ejected air is directed toward the center of the sheet  9 .  
         [0048]    In the sheet stacking device in FIG. 2B, the air ejection port  3  is provided in an area A 2  that is located downstream in the sheet delivery direction on the side whereat the stopper  4  is provided, so that the ejected air is directed toward the center of the sheet  9 .  
         [0049]    In the sheet stacking device in FIG. 2C, the air ejection port  3  is provided in an area A 3  that is located upstream in the sheet delivery direction, so that the ejected air is directed toward the center of the sheet  9 .  
         [0050]    As a result of the experiments conducted for the sheet stacking devices for which the air ejection port  3  was provided in the three different areas A 1 , A 2  and A 3 :  
         [0051]    (1) For the sheet stacking device in FIG. 2A for which the air ejection port  3  was located in area A 1 , the stacking state was considered to be satisfactory.  
         [0052]    The ejection of air did not need to be performed continuously; intermittent air ejection was sufficient. Specifically, when for one sheet air was intermittently ejected about five times at a pressure of 5 to 10 Kg/cm 2 , the stacking state was satisfactory.  
         [0053]    (2) For the sheet stacking device in FIG. 2B for which the air ejection port  3  was located in area A 2 , a stacking state was obtained that was inferior to the state obtained in (1). However, when in addition to the stopper  4  a stopper  4 ′ was located at a position indicated by the broken lines, a satisfactory stacking state was obtained.  
         [0054]    (3) For the sheet stacking device in FIG. 2C for which the air ejection port  3  was located in area A 3 , with a large sheet a satisfactory stacking state was not obtained.  
         [0055]    The reason the stacking state was unsatisfactory is that when a large sheet is employed the air pressure must be increased, and at a high pressure the rear edge of a sheet  9  is attracted to the air nozzle due to the associated air, and that, when the air pressure was low, the sheets could not be stacked neatly.  
         [0056]    From the above results, it is preferable that the air be blown from the L-shaped area A 1  in FIG. 1C toward the center of the sheet.  
         [0057]    Further, it was found that the air ejection port  3  may be located anywhere in area A 1  so long as the air is ejected toward the center of the sheet  9 .  
         [0058]    It was found that the air need not be blown continuously, but intermittently, five times per sheet, to obtain a satisfactory stacking state. The air pressure at that time was 5 to 10 Kg/cm 2 .  
         [0059]    The intermittent cycle should correlate with the distance the sheet is transported. When the intermittent cycle provides, for example, for air to be ejected once every 5 to 20 cm as the sheet is transported, the same effect as that provided by a continuous operation is obtained with a corresponding saving in energy.  
         [0060]    Furthermore, air ejection is required only during a period extending from the time the sheet  9  is output at the sheet discharge port until it is halted. Therefore, a sheet sensor (not shown) for detecting the discharge of the sheet is provided at a proper location, and since the sheet sensor detects a period extending from the time the sheet is discharged until it is halted at the stopper  4 , air must be ejected continuously or intermittently need only during that period and a saving in energy can be realized.  
         [0061]    As is described above, according to the first embodiment, less energy will be consumed and the sheets  9  will be neatly and appropriately stacked at the predetermined stopper  4 .  
         [0062]    [0062]FIGS. 3A to  3 C are schematic diagrams illustrating a sheet stacking device for a second embodiment of the present invention.  
         [0063]    [0063]FIG. 3A is a side view of the sheet stacking device, FIG. 3B is a front view thereof, and FIG. 3C is a plan view thereof.  
         [0064]    A sheet delivery unit  1  comprises: discharging rollers  2 , for the external discharge of a sheet by the sheet delivery unit  1 ; an air ejection port  3 , which is the feature of the present invention; a stopper  4 ; a fan  5 ; and a slide face  6 , along which a sheet  9  that is being discharged slides. The slide face  6  also serves as the top of a case for the printer that includes the sheet delivery unit  1 . The air ejection port  3  is located near the sheet discharge port, so that air is ejected from the rear of the sheet  9  that is being discharged. In the second embodiment the sheet stacking device is constituted by the air ejection port  3  through which air is ejected toward the bottom of the sheet, the stopper  4 , the fan  5 , and the slide face  6 .  
         [0065]    An explanation will now be given for the processing for the second embodiment for blowing air toward the bottom of a sheet that is discharged.  
         [0066]    A sheet  9 , which is sandwiched between the two upper and lower discharging rollers  2 , is discharged externally by the sheet delivery unit  1 . When the sheet is discharged by the discharging rollers  2 , the fan  5  is rotated and air is blew through the air ejection port toward the bottom of the sheet  9 . The sheet  9  is transported along the slide face  6  in the direction indicated by a white arrow, and is held at the stopper  4 .  
         [0067]    Thereafter, succeeding sheets  9  are held at the stopper  4  in the same manner. Since the force of the air expelled from the air ejection port  3  is exerted against all the sheets  9  that are held at the stopper  4  and an air layer is formed between the individual sheets, the contact area of the sheets can be reduced and a satisfactory stacking state can be obtained.  
         [0068]    As the result of various experiments, it was found that for the second embodiment the air flow rate is particularly important.  
         [0069]    (1) If the air flow rate was too high, the sheets were raised too much. And when rolled sheets were employed, the sheets curled up.  
         [0070]    (2) If the air flow rate was too low, the sheets were not raised sufficiently, so that the stacking of the sheets was not satisfactory.  
         [0071]    In the second embodiment as well as in the first embodiment, air did not have to be ejected continuously, and to obtain a satisfactory stacking state air was ejected intermittently, five times for each sheet. An air flow rate of 70 to 120 litters a minute was used .  
         [0072]    When the air is ejected toward the sheet, the lower edge of the right side of the sheet  9  is held at the stopper, so that this embodiment can be applied for all types of sheets  9 , regardless of the paper size.  
         [0073]    Further, as in the first embodiment, air ejection is required only during a period extending from the time the sheet  9  is discharged until it is halted. Therefore, a sheet sensor (not shown) for detecting the discharge of the sheet is provided at a proper position, and since the sheet sensor can detect a period extending from the time the sheet is discharged until it is halted at the stopper  4 , air must be continuously or intermittently ejected only during that period, so that a saving in energy can be achieved.  
         [0074]    As is described above, according to the first embodiment, the sheets  9  can be neatly and appropriately stacked at the predetermined stopper  4 , and the consumption of energy can be reduced.  
         [0075]    As is described above, according to the present invention, since (1) air is ejected toward the side of a sheet when it is discharged, or (2) air is ejected toward the bottom of a sheet when it is discharged, sheets can be stacked satisfactorily, regardless of the shape and the thickness of the sheets, and the material of which they are composed.