Patent Publication Number: US-10315870-B2

Title: Sheet feeding device, image forming apparatus incorporating the sheet feeding device, and image forming system incorporating the sheet feeding device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2017-029639, filed on Feb. 21, 2017, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     This disclosure relates to a sheet feeding device, an image forming apparatus incorporating the sheet feeding device, and an image forming system incorporating the sheet feeding device. 
     Related Art 
     Sheet feeding devices included in an image forming apparatus are known to convey an uppermost sheet placed on a sheet bundle loaded on a sheet loading table such as a sheet container, to a sheet attraction belt that functions as an attracting and conveying device. 
     A known sheet feeding device has the configuration in which an uppermost sheet placed on a sheet bundle loaded on a sheet loading table is attracted to the surface of a sheet attraction belt by suction air applied by an air drawing portion that includes an air drawing fan that functions as an air drawing device, and then is conveyed to an apparatus body of an image forming apparatus. In this known sheet feeding device, after the last sheet on which an image is to be formed is fed, the air drawing fan is stopped to terminate an air drawing operation performed by the air drawing portion. Therefore, detachment of the sheet container is restrained until a predetermined time is completely elapses. This predetermined time is an estimated duration to take the sheet attached to the sheet attraction belt to be peeled off or separated from the sheet attraction belt. Accordingly, after completion of image formation, the sheet container can be detached safely without causing any damage to the sheet by, for example, a sheet peeling claw or claws. 
     SUMMARY 
     At least one aspect of this disclosure provides a sheet feeding device including a sheet loader, an air drawing body; an attracting and conveying device, an air duct and a blocking device. The sheet loader is a device on which a bundle of sheets is loaded. The air drawing body is configured to generate suction air. The attracting and conveying device is configured to attract a sheet on top of the bundle of sheets by the suction air and convey the sheet. The air duct is configured to intake the suction air drawn by the air drawing body, to the attracting and conveying device. The blocking device is configured to block the suction air in the air duct. 
     Further, at least one aspect of this disclosure provides an image forming apparatus including an image forming device configured to form an image on a sheet, and the above-described sheet feeding device configured to feed the sheet toward the image forming device. 
     Further, at least one aspect of this disclosure provides an image forming system including an image forming apparatus including an image forming device configured to form an image on a sheet, and the above-described sheet feeding device configured to feed the sheet toward the image forming device. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       An exemplary embodiment of this disclosure will be described in detail based on the following figured, wherein: 
         FIG. 1  is a diagram illustrating a schematic configuration of an image forming system according to an embodiment of this disclosure; 
         FIG. 2  is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of this disclosure; 
         FIG. 3  is a schematic diagram illustrating the sheet feeding device according to an embodiment of this disclosure; 
         FIG. 4  is a perspective vie rating a sheet tray included in the sheet feeding device; 
         FIG. 5  is a diagram illustrating a sheet feeding unit included in the sheet feeding device, viewed from a rear side of the sheet feeding unit; 
         FIGS. 6A, 6B and 6C  are schematic diagrams illustrating an air drawing device included in the sheet feeding unit in a state in which a shutter valve of the air drawing device is open; 
         FIGS. 7A, 7B and 7C  are schematic diagrams illustrating the air drawing device in a state in which the shutter valve of the air drawing device is closed; 
         FIG. 8  is a block diagram illustrating a configuration of a control system included in the sheet feeding device according to an embodiment of this disclosure; 
         FIG. 9  is a flowchart of an example of sheet conveying operations; 
         FIG. 10  is a flowchart of an example of operations after completion of sheet attracting and conveying operations; 
         FIG. 11  is a diagram illustrating another example of the sheet feeding device according to an embodiment of this disclosure; 
         FIGS. 12A and 12B  are diagrams illustrating a lower air drawing fan and a shutter mechanism; 
         FIG. 13  is a block diagram illustrating another configuration of a control system included in the sheet feeding device according to an embodiment of this disclosure; 
         FIG. 14  is a flowchart of another sheet feeding operations of the sheet feeding device; 
         FIG. 15  is a flowchart of another example of operations after completion of sheet attracting and conveying operations; 
         FIG. 16  is a diagram illustrating opening and closing of the shutter valve and movement of a sheet in the sheet feeding device; 
         FIG. 17  is a diagram illustrating movement of the sheet when a lower air drawing force is increased; and 
         FIG. 18  is a diagram illustrating the movement of the sheet when a sheet loader is lowered. 
     
    
    
     DETAILED DESCRIPTION 
     It will be understood that if an element or layer is referred to as being “on”, “against”, “connected to” or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to” or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers referred to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements describes as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors herein interpreted accordingly. 
     Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layer and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present disclosure. 
     The terminology used herein is for describing particular embodiments and examples and is not intended to be limiting of exemplary embodiments of this disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Descriptions are given, with reference to the accompanying drawings, of examples, exemplary embodiments, modification of exemplary embodiments, etc., of an image forming apparatus according to exemplary embodiments of this disclosure. Elements having the same functions and shapes are denoted by the same reference numerals throughout the specification and redundant descriptions are omitted. Elements that do not demand descriptions may be omitted from the drawings as a matter of convenience. Reference numerals of elements extracted from the patent publications are in parentheses so as to be distinguished from those of exemplary embodiments of this disclosure. 
     This disclosure is applicable to any image forming apparatus, and is implemented in the most effective manner in an electrophotographic image forming apparatus. 
     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this disclosure is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes any and all technical equivalents that have the same function, operate in a similar manner, and achieve a similar result. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, preferred embodiments of this disclosure are described. 
     Now, a description is given of a sheet feeding device according to an embodiment of this disclosure. 
       FIG. 1  is a diagram illustrating a schematic configuration of an image forming system  1  according to an embodiment of this disclosure. 
     The image forming apparatus  100  may be a copier, a facsimile machine, a printer, a multifunction peripheral or a multifunction printer (MFP) having at least one of copying, printing, scanning, facsimile, and plotter functions, or the like. According to the present example, the image forming apparatus  100  is an electrophotographic printer that prints toner images on recording media by electrophotography. 
     It is to be noted in the following examples that: the term “image forming apparatus” indicates an apparatus in which an image is formed on a recording medium such as paper, OHP (overhead projector) transparencies, OHP film sheet, thread, fiber, fabric, leather, metal, plastic, glass, wood, and/or ceramic by attracting developer or ink thereto; the term “image formation” indicates an action for providing (i.e., printing) not only an image having meanings such as texts and figures on a recording medium but also an image having no meaning such as patterns on a recording medium; and the term “sheet” is not limited to indicate a paper material but also includes the above-described plastic material (e.g., a OHP sheet), a fabric sheet and so forth, and is used to which the developer or ink is attracted. In addition, the “sheet” is not limited to a flexible sheet but is applicable to a rigid plate-shaped sheet and a relatively thick sheet. 
     Further, size (dimension), material, shape, and relative positions used to describe each of the components and units are examples, and the scope of this disclosure is not limited thereto unless otherwise specified. 
     Further, it is to be noted in the following examples that: the term “sheet conveying direction” indicates a direction in which a recording medium travels from an upstream side of a sheet conveying path to a downstream side thereof; the term “width direction” indicates a direction basically perpendicular to the sheet conveying direction. 
     As illustrated in  FIG. 1 , the image forming system  1  includes an image forming apparatus  100  and a sheet feeding device  200 . The image forming apparatus  100  forms an image on a sheet. The sheet feeding device  200  feeds the sheet to the image forming apparatus  100 . The sheet feeding device  200  is disposed on a side face of a housing of the image forming apparatus  100 . 
     A description is given of an entire configuration and functions of the image forming apparatus  100  such as a printer and a copier, according to an embodiment of this disclosure. The image forming apparatus  100  may include a sheet feeding device according to an embodiment of this disclosure. 
       FIG. 2  is a schematic diagram illustrating the image forming apparatus  100  according to the present embodiment of this disclosure. 
     The image forming apparatus  100  has printing and copying functions for forming a full color image with four color toners such as yellow (Y), magenta (M), cyan (C) and black (K). As illustrated in  FIG. 2 , the image forming apparatus  100  includes four image forming units  101 Y,  101 M,  101 C and  101 K. The image forming units  101 Y,  101 M,  101 C and  101 K that form respective single color images are aligned at an upper part of the housing of the image forming apparatus  100 . The image for units  101 Y,  101 M,  101 C and  101 K have a substantially identical configuration and functions to each other. Therefore, following details of the image forming units  101 Y,  101 M,  101 C and  101 K are described with a single image forming unit that corresponds to each of the image forming units  101 Y,  101 M,  101 C and  101 K, without the suffixes Y, M, C and K indicating respective colors. The image forming unit  101  (i.e., the image forming units  101 Y,  101 M,  101 C and  101 K) includes a photoconductor drum  102  (i.e., photoconductor drums  102 Y,  102 M,  102 C and  102 K), a charger  103  (i.e., chargers  103 Y,  103 M,  103 C and  103 K), a developing device  104  (i.e., developing devices  104 Y,  104 M,  104 C and  104 K) and a cleaning device  105  (i.e., cleaning devices  105 Y,  105 M,  105 C and  105 K). The charger  103 , the developing device  104 , and the cleaning device  105  are disposed around the photoconductor drum  102 . Further, an optical writing device  107  is disposed above the photoconductor drum  102 . 
     An intermediate transfer belt  108  is disposed below the image forming units  101 Y,  101 M,  101 C and  101 K. The intermediate transfer belt  108  is wound around multiple support rollers. As one of the multiple support rollers is driven by a drive unit, the intermediate transfer belt  108  is rotated in a direction indicated by arrow A in  FIG. 1 . A transfer roller  106  (i.e., transfer rollers  106 Y,  106 M,  106 C and  106 K) that functions as a primary transfer unit is disposed facing the photoconductor drum  102  of the image forming unit  101  with the intermediate transfer belt  108  interposed therebetween. When the transfer roller  106  and the photoconductor drum  102  contact with the intermediate transfer belt  108  interposed therebetween, a primary transfer portion is formed to primarily transfer the toner image onto the photoconductor drum  102 . 
     It is to be noted that the image forming unit  101  (i.e., the image forming units  101 Y,  101 M,  101 C and  101 K), the transfer roller  106  (i.e., the transfer rollers  106 Y,  106 M,  106 C and  106 K) and the intermediate transfer belt  108  function as an image forming device. 
     In the image forming unit  101 , the photoconductor drum  102  is rotated in a counterclockwise direction in  FIG. 1 . Then, the charger  103  uniformly charges a surface of the photoconductor drum  102  to a predetermined polarity. Then, an optically modulated laser light beam is emitted from the optical writing device  107 , so that an electrostatic latent image is formed on the charged surface of the photoconductor drum  102 . The electrostatic latent image is developed with toner applied by the developing device  104  into a visible toner image. The visible toner images of respective single colors formed by the image forming units  101 Y,  101 M,  101 C and  101 K are sequentially transferred in layers onto a surface of the intermediate transfer belt  108 . 
     By contrast, a sheet feeding section  114  that functions as a sheet feeding device included in the image forming apparatus  100  is disposed in a lower part of the housing of the image forming apparatus  100 . The sheet feeding section  114  includes sheet trays  114   a  and  114   b.  A sheet that functions as a recording medium is fed out from one of the sheet feeding section  114  and the sheet feeding device  200  that is attached to the image forming apparatus  100 . The fed sheet is conveyed to a pair of registration rollers  111  in a direction indicated by arrow B in  FIG. 2 . 
     The sheet contacted and temporarily stopped at the pair of registration rollers  111  is fed out from the pair of registration rollers  111  in synchronization with movement of the toner image formed on the surface of the intermediate transfer belt  108 . Then, the sheet is conveyed to a secondary transfer portion where a secondary transfer roller  109  contacts the intermediate transfer belt  108 . A voltage having an opposite polarity to a toner charge polarity is applied to the secondary transfer roller  109 . By so doing, the composite toner image (the full color image) formed on the surface of the intermediate transfer belt  108  is transferred onto the sheet. After the toner image has been transferred to the sheet, the sheet is conveyed by a sheet conveying belt  112  to a fixing device  113 . In the fixing device  113 , the toner image is fixed to the sheet by application of heat and pressure. After the toner image is fixed to the sheet, the sheet is ejected out of the housing of the image forming apparatus  100  as indicated by arrow C in  FIG. 2  onto a sheet ejection tray. 
     It is to be noted that, when the sheet is ejected with the back of the sheet facing up in the single-side printing (a face down ejection), the sides (i.e., the front and the back) of the sheet are reversed by ejecting the sheet outside the housing of the image forming apparatus  100  as indicated by arrow C in  FIG. 1  via a sheet reverse portion  115 . Further, in the duplex printing, the pair of registration rollers  111  after the toner image has been fixed thereto is conveyed via a duplex reverse portion  116  from a reentry passage  117  to the pair of registration rollers  111  again. By so doing, a toner image formed on the surface of the intermediate transfer belt  108  is transferred onto the back of the sheet. After the toner image has been transferred onto the sheet, the toner image is fixed to the sheet in the fixing device  113 . Then, similar to the single-side printing, the sheet is ejected out in the direction C in  FIG. 1  directly from the fixing device  113  or via the sheet reverse portion  115 . In addition, switching claws  118  and  119  are disposed appropriately to switch a sheet conveying direction. 
     In a case of a monochrome printing, the image forming apparatus  100  according to the present embodiment uses the image forming unit  101 K to form a monochrome toner image and transfers the monochrome toner image onto a sheet via the intermediate transfer belt  108 . A sheet having a monochrome toner image thereon is handled along the same process as a sheet having a full color toner image after the toner image is fixed to the sheet. 
     It is to be noted that the image forming apparatus  100  further includes a toner bottle set  120  on an upper face of the housing. The toner bottle set  120  sets respective color toner bottles  121  (i.e., toner bottles  121 Y,  121 M,  121 C and  121 K) that contains toner to be supplied to the developing device  104  of the image forming unit  101 . Further, the image forming apparatus  100  further includes an operation unit  124  that includes a display  122  and a control panel  123 . In addition, a sheet feeding device is provided on the right side of the housing of the image forming apparatus  100  in  FIG. 2 . A sheet conveyed from the sheet feeding device  200  ( FIG. 3 ) comes in the housing of the image forming apparatus  100  through the sheet entrance D. At the sheet entrance D, a bypass tray opening  125  and a pair of bypass rollers  126  are provided. The sheet is received through the bypass tray opening  125  and then is conveyed by the pair of bypass rollers  126 . 
       FIG. 3  is a diagram illustrating a schematic configuration of the sheet feeding device  200  according to the present embodiment of this disclosure. The sheet feeding device  200  is disposed on the side face of the housing of the image forming apparatus  100 . 
     The sheet feeding device  200  includes two sheet trays  10  disposed vertically to each other (i.e., a lower sheet tray  10  and an upper sheet tray  10 ). Each of the sheet trays  10  includes a sheet loading table  11  that functions as a sheet loader on which a sheet bundle SB is loaded. In the present embodiment, each of the sheet trays  10  can contain up to about 2500 sheets therein. It is to be noted that the term “sheet” includes plain paper, coated paper, label paper, OHP sheet and film, and the like. A sheet feeding unit  20  is disposed above the corresponding sheet tray  10 . The sheet feeding unit  20  separates and feeds a sheet loaded on the sheet tray  10 . The sheet feeding unit  20  includes a sheet attraction belt  21  and an air drawing device  23 , both functioning as an attracting and conveying device. 
     Each sheet loaded on the lower sheet tray  10  passes through a lower conveying passage  82  to be conveyed by a pair of outlet rollers  80  to the housing of the image forming apparatus  100 . Similarly, each sheet loaded on the upper sheet tray  10  passes through an upper conveying passage  81  to be conveyed by the pair of outlet rollers  80  to the housing of the image forming apparatus  100 . 
     Further, each of the sheet trays  10  further includes a sheet face detection sensor  31  to detect a floating sheet that is lifted by an air blowing device to control vertical movement of the sheet loading table  11 . 
       FIG. 4  is a perspective view illustrating one of the sheet trays  10  included in the sheet feeding device  200 . 
     The sheet attraction belt  21  of the sheet feeding unit  20  is stretched by two tension rollers  22   a  and  22   b  and includes multiple air drawing openings over an entire region in a circumferential direction thereof. The multiple air drawing openings penetrate through the sheet attraction belt  21  from a front face side to a back face side thereof. An air drawing device  23  is disposed within an inner loop of the sheet attraction belt  21 . The air drawing device  23  is coupled with an air drawing fan  61  that functions as an air drawing body to intake air via an air duct  41  that functions as an air flowing passage. As the air drawing device  23  generates a negative pressure in a lower area, a sheet P is attracted to a lower face of the sheet attraction belt  21 . A detailed description of the air drawing device  23  is described below. 
     Further, each sheet tray  10  includes an air blowing device  17  that functions as an air blower to blow air to the upper sheets of the sheet bundle SB. The air blowing device  17  includes a front air blowing device  12  and a side air blowing device  14 . 
     The front air blowing device  12  is disposed at a downstream side end in the sheet conveying direction and a side plate is disposed facing the leading end of the sheet P of the sheet bundle SB. As the sheet bundle SB contacts or abuts the side plate of the front air blowing device  12 , the side plate of the front air blowing device  12  regulates a leading end position of the sheet bundle SB in the sheet conveying direction. The front air blowing device  12  that functions as a floating air blower and a separating air blower and blows air to the leading end of the upper part of the sheet bundle SB (i.e., a downstream side end in the sheet conveying direction). The front air blowing device  12  includes a floating nozzle, a separation nozzle, and two air blowing fans  15 . The floating nozzle guides air in a direction to float the sheet bundle SB. The separation nozzle guides air in a direction to separate an uppermost floating sheet and other floating sheet(s). The two air blowing fans  15  (hereinafter, simply referred to as an air blowing fan  15 ) blow air to the floating nozzle and the separation nozzle. Air that is blown from the floating nozzle in a direction indicated by arrow a 1  in  FIG. 4  is referred to as floating air. Air that is blown from the separation nozzle in a direction indicated by arrow a 2  in  FIG. 4  is referred to as separation air. The floating air and the separation air are discharged from respective portions facing the leading end of the upper sheets of the sheet bundle SB (i.e., the downstream side end in the sheet conveying direction). Consequently, the floating air and the separation air are blown to the leading end of the upper sheets of the sheet bundle SB (i.e., the downstream side end in the sheet conveying direction). 
     The side air blowing device  14  is mounted on both sides of a pair of side fences  13  to blow air in a direction indicated by arrow b in  FIG. 4 , to the side face of the upper sheets of the sheet bundle SB. The side air blowing device  14  includes a side floating nozzle that flips and separates the sheets P in bundle and guides air to a direction to lift the sheets P. Air that is blown from the side floating nozzle in the direction indicated by arrow b in  FIG. 4  is referred to as side air. The side air is discharged from an air discharging port that is provided at a portion of each of the pair of side fences  13 , facing the upper side of the sheet bundle SB. Consequently, the floating air is discharged from the air discharging port and is blown to the side face of the upper side of the sheet bundle SB. Due to the front air blowing device  12  and the air discharged and blown through the air discharging ports of the pair of side fences  13 , the upper sheet of the sheet bundle SB is lifted to float. 
     Further, each sheet tray  10  includes an end fence  25  to align the trailing end of the sheet bundle SB loaded on the sheet loading table  11 . 
     Next, a detailed description of the air drawing device  23  is described. 
       FIG. 5  is a diagram illustrating the sheet feeding unit  20  included in the sheet feeding device  200 , viewed from a rear side of the sheet feeding unit  20 . 
     As illustrated in  FIG. 5 , the air drawing device  23  is disposed in an inner loop of the sheet attraction belt  21 . A sheet attracting unit  30  in which the attracting and conveying device (i.e., the sheet attraction belt  21 ) attracts the uppermost sheet and the air drawing fan  61  are connected via the air duct  41 . Suction air that is drawn by the sheet drawing fan drawing fan flows in a direction indicated by arrow c 1  and a direction indicated by arrow c 2  in  FIG. 4 . 
       FIGS. 6A, 6B and 6C  are schematic diagrams illustrating the air drawing device  23  in a state in which a shutter valve  42  of the air drawing device  23  is open.  FIG. 6A  is a perspective view illustrating an inside of the air duct  41 .  FIG. 6B  is a side view illustrating the air duct  41  viewed in an x-axis direction.  FIG. 6C  is a side view illustrating the air duct  41  viewed in a z-axis direction. 
       FIGS. 7A, 7B and 7C  are schematic diagrams illustrating the air drawing device  23  in a state in which a shutter valve  42  of the air drawing device  23  is closed.  FIG. 7A  is a perspective view illustrating an inside of the air duct  41 .  FIG. 7B  is a side view illustrating the air duct  41  viewed in an x-axis direction.  FIG. 7C  is a side view illustrating the air duct  41  viewed in a z-axis direction. 
     As illustrated in  FIG. 6A , in the air drawing device  23  in the present embodiment, the shutter valve  42  that functions as a blocking unit to Hock air passage in the air duct  41 . 
     The shutter valve  42  is coupled to a solenoid via a tension spring. A controller  60  controls ON and OFF of the solenoid to switch shut down and passage of suction air in the air duct  41 . 
     To be more specific, when the solenoid is in a non-energized state in which an air drawing force of the solenoid is not acting, that is, in an OFF state, the shutter valve  42  is pulled by a spring. Therefore, the shutter valve  42  is disposed parallel to an air drawing direction, which is in an open state. By driving the air drawing fan in this state, suction air flows from the sheet attracting unit  30  in a direction indicated by arrow c 3  and a direction indicated by arrow c 4  in  FIG. 7A . By contrast, when the solenoid is completely drawn, that is, in an ON state, the flow of the suction air drawn by the air drawing fan is shut down in the air duct  41 , which is a closed state. By driving the air drawing fan in this state, the suction air flowing the direction indicated by arrow c 4  is shut down by the shutter valve  42 . 
     As illustrated in  FIG. 6B , a leak hole  44  is provided on the side wall of the air duct  41 , so as to penetrate or go through the inside of the air duct  41  to connect with the outside of the air duct  41 . Shielding portions  42   a,  each of which functioning as a shielding body, are provided at both ends in a width direction of the shutter valve  42 , so as to block the leak hole  44  provided to the air duct  41 . When the shutter valve  42  is open, the leak hole  44  is blocked by the shielding portions  42   a.  By contrast, when the shutter valve  42  is dosed, the position of the shielding portions  42   a  move along with rotation of the shutter valve  42 . According to this movement, the leak hole  44  opens to reduce the static pressure of air suction of the sheet attracting unit  30 . 
     Next, a description is given of a control of a sheet feeding operation according to the present embodiment of this disclosure. 
       FIG. 8  is a block diagram illustrating an example of a configuration of a control system of the sheet feeding device  200  according to an embodiment of this disclosure. 
     As illustrated in  FIG. 8 , the controller  60  that functions as a controller of the sheet feeding device  200  includes the air blowing device  17  to blow air toward the front air blowing device  12  and the side air blowing device  14 , the air drawing fan  61  coupled with the air drawing device  23 , the sheet attraction belt  21 , and a solenoid  43  to causes the shutter valve  42  to start working. The controller  60  is further connected to a sheet feed working state LED (light emitting diode)  62  that functions as a working state indicator to display the working state of the sheet feeding device  200 , and an elevation drive motor  19  that functions as a loader elevation device to lift and lower the sheet loading table  11 . 
     Next, a description is given of operations when the attracting and conveying device (such as the sheet attraction belt  21  and an air drawing device  23 ) conveys sheets one by one. 
       FIG. 9  is a flowchart of an example of sheet conveying operations. 
     A general controller of the image forming apparatus  100  receives an image forming instruction associated with the sheets set in the sheet trays  10  of the sheet feeding device  200  via a control panel of the image forming apparatus  100 . (Hereinafter, “the sheet trays  10 ” is also be referred to simply as “the sheet tray  10 .”) Then, the general controller transmits a sheet feeding instruction to the controller  60  of the sheet feeding device  200  and information of types of sheet loaded on the sheet loading table  11  of the sheet trays  10 . On receipt of the sheet feeding instruction, the controller  60  starts driving the air blowing device  17  while movement of the sheet attraction belt  21  is being stopped. Accordingly, as illustrated in  FIG. 4 , air is discharged from the air discharging port of the front air blowing device  12  in a direction indicted by arrow al. Therefore, the air is blown to a front end part of the upper part of the sheet bundle SB. Further, air is discharged from the air discharging port of the pair of side fences  13  to be blown to the side end of the upper side of the sheet bundle SB. Due to the air discharged and blown through the air discharging ports of the front air blowing device  12  and through the air discharging ports of the pair of side fences  13 , the upper sheet of the sheet bundle SB is lifted to float. 
     At the same time, the controller  60  starts driving the air drawing fan  61  to start air drawing by the air drawing device  23  (step S 1 ). As the air drawing device  23  starts air drawing, the air drawing device  23  generates a negative pressure in the lower area, and a floating uppermost sheet P 1  is attracted to the sheet attraction belt  21 . Then, as the sheet attraction belt  21  rotates, the sheet feeding operation starts (step S 2 ). 
     Then, the controller  60  determines whether or not the predetermined time has passed from the start of the sheet feeding operation (step S 3 ). When step S 3  is NO and the predetermined time has not yet passed, the process repeats step S 3 . When step S 3  is YES and the predetermined time has passed, the shutter valve  42  is closed (step S 4 ), and rotation of the sheet attraction belt  21  is stopped (step S 5 ) 
     By stopping the sheet attraction belt  21  after a predetermined time has elapsed from the start of the sheet feeding operation, when the trailing end of the uppermost sheet P 1  passes an attraction opening, a subsequent sheet on the sheet bundle SB loaded on the sheet tray  10  is prevented from being attracted by the sheet attraction belt  21  and from being conveyed at an unintended timing. 
     Further, by closing the shutter valve  42  after the predetermined time has passed from the start of the sheet feeding operation, attraction of the sheet attraction belt  21  to the sheet is stopped. Accordingly, the sheet attraction belt  21  is prevented from damages or scratches caused during the sheet conveying operation due to contact of the sheet that has been attracted to the sheet attraction belt  21  with the sheet attraction belt  21  stopped when conveyed by the attracting and conveying device. 
     Then, the controller  60  determines whether or not a predetermined time has passed from the stop of the sheet attraction belt  21  (step S 6 ). When step S 6  is NO and the predetermined time has not yet passed, the process repeats step S 6 . When step S 6  is YES and the predetermined time has passed, the shutter valve  42  is opened to convey a subsequent sheet (step S 7 ), and determines whether or not the start of the sheet feeding operation is requested (step S 8 ). As described above, by opening the shutter valve  42  whether there is a request of the start of the sheet conveying operation or not, the sheet attracting and conveying operation can be performed whenever the start of the sheet feeding operation is requested, and therefore a high productivity can be obtained. 
     When step S 8  is YES and the start of the sheet feeding operation is requested, step S 2  through step S 7  are repeated to convey the subsequent sheet. When step S 8  is NO and the start of the sheet feeding operation is not requested, the sheet attracting and conveying operation is finished, then the controller  60  executes another operation flow after the sheet attracting and conveying operation. 
     Next, a description is given of the operations after completion of the sheet attracting and conveying operation, according to the present embodiment of this disclosure. 
       FIG. 10  is a flowchart of an example of operations after completion of the sheet attracting and conveying operation. 
     When the sheet attracting and conveying operation performed by the sheet attracting and conveying device is completed, the controller  60  causes the air drawing fan  61  to stop (step S 11 ), arid the shutter valve  42  to be closed (step S 12 ). At this time, the leak hole that has been closed by the shutter valve  42  becomes open. When the sheet feeding device  200  according to the present embodiment is compared with a comparative sheet feeding device, the negative pressure of an attracting and conveying portion is not released in the comparative sheet feeding device. Therefore, it takes more time that a sheet separates from the attracting and conveying portion. By contrast, in the present embodiment, when attraction of a sheet by the air drawing is interrupted, the negative pressure in the sheet attracting unit  30  is released, and therefore the sheet can be separated from the sheet attraction belt  21  quickly. Then, the controller  60  determines whether or not the predetermined time has passed since the shutter valve  42  is closed (step S 13 ). When S 13  is NO and the predetermined time has not yet passed, the process repeats step S 13 . When step S 13  is YES and the predetermined time has passed, the shutter valve  42  is open (step S 14 ). As described above, by opening the shutter valve  42  after the predetermined time has elapsed, when a print job is requested and the air drawing fan  61  starts a sheet attracting operation, the step of opening the shutter valve  42  can be omitted. 
     Then, the controller  60  causes the shutter valve  42  to open and turns off the sheet feed working state LED  62  (step S 15 ) simultaneously, and so as to indicate a user that the sheet tray  10  is ready to open. 
     As described above, by opening the shutter valve  42  when the sheet tray  10  is to be opened, that is, by turning off the solenoid  43 , a user can be prevented from touching the heated solenoid  43 , and therefore can be safe. 
     Next, a description is given of another example of configuration of the sheet feeding device  200 . 
       FIG. 11  is a diagram illustrating another example of the sheet feeding device  200  according to an embodiment of this disclosure.  FIGS. 12A and 12B  are diagrams illustrating a lower air drawing fan and a shutter mechanism. 
     As illustrated in  FIG. 11 , the sheet feeding unit  20  includes the sheet attraction belt  21  and the air drawing device  23 , which is basically the same configuration as the above described embodiment. That is, the sheet attraction belt  21  is stretched by the two tension rollers  22   a  and  22   b  and the air drawing device  23  is disposed within the inner loop of the sheet attraction belt  21 . The air drawing device  23  is coupled with the drawing fan that functions as an air drawing unit to intake air via the air duct that functions as an air flowing passage. As the air drawing device  23  generates a negative pressure in a lower area, the sheet P is attracted to a lower face of the sheet attraction belt  21 . 
     The front air blowing device  12  includes a floating nozzle  51  and a separation nozzle  52 . The floating nozzle  51  guides air to discharge in the direction to float a sheet P. The separation nozzle  52  guides air to discharge in a direction to separate an uppermost floating sheet and other floating sheet(s). Floating air is discharged from the floating nozzle  51  in the direction indicated by arrow a 1  in  FIG. 11  and separation air is discharged from the separation nozzle  52  in the direction indicated by arrow a 2  in  FIG. 11 . Consequently, the floating air and the separation air are blown to the leading end of the upper sheets of the sheet bundle SB (i.e., the downstream side end in the sheet conveying direction). Accordingly, sheets P on the upper part of the sheet bundle SB are lifted and floated. As illustrated in  FIG. 11 , an air duct  51   a  is disposed between air blowing fans and is coupled to the floating nozzle  51  of the front air blowing device  12 . Further, as illustrated in  FIG. 11 , an air duct  52   a  is disposed between air blowing fans and is coupled to the separation nozzle  52  of the front air blowing device  12 . A shutter valve  51   b  that functions as an air blocking body is disposed in the air duct  51   a  to shut and open air inside the air duct  51   a.  Similarly, a shutter valve  52   b  that functions as a blocking body is disposed in the air duct  52   a  to shut and open air inside the air duct  52   a.    
     Further, the front air blowing device  12  includes a lower air drawing nozzle  53  to draw air so as to direct an air drawing force toward a lower direction relative to the sheet in the vicinity of the uppermost sheet. As illustrated in  FIGS. 12A and 12B , the lower air drawing nozzle  53  is coupled to a lower air drawing fan  54  that functions as a lower air drawing body to draw air via an air duct  53   a  that functions as a lower air drawing air duct. Consequently, the air in the vicinity of the uppermost sheet is drawn to the lower air drawing nozzle  53  in a direction indicated by arrow a 3  in  FIG. 11 . A shutter valve  53   b  that functions as a lower suction air opening and closing device is disposed inside the air duct  53   a  of the air drawing device  23  to block and open air flow inside the air duct  53   a.    
     Further, as illustrated in  FIG. 12B , when a solenoid  55  is in a non-energized state in which an air drawing three of the solenoid  55  is not acting, that is, in an OFF state, the shutter valve  53   b  is pulled by a spring  56 . Therefore, the shutter valve  53   b  shuts down air in the air duct  53   a,  which is in a closed state. When the solenoid  55  completely attracts a plunger  55   a,  that is, in an ON state, a lever  57  that is coupled to the plunger  55   a  is turned to move the shutter valve  53   b  toward a direction indicated by arrow d in  FIG. 12B . By so doing, the closed state in which air flow in the air duct  53   a  is shut down is released, and therefore the suction air flows in a direction indicated by arrow e in  FIG. 12B . 
     Next,  FIG. 13  is a block diagram illustrating another configuration of a control system included in the sheet feeding device  200  according to an embodiment of this disclosure. 
     As illustrated in  FIG. 13 , the controller  60  that functions as a controller of the sheet feeding device  200  includes the air blowing device  17  to blow air toward the front air blowing device  12  and the side air blowing device  14 , the air drawing fan  61  coupled with the air drawing device  23 , the sheet attraction belt  21 , and the solenoids  43  and  55  to causes the shutter valves  42  and  53   b  to start working, respectively. The controller  60  is further connected to the sheet feed working state LED  62  that functions as a working state indicator to indicate or display the working state of the sheet feeding device  200 , the elevation drive motor  19  that functions as a loader elevation device to lift and lower the sheet loading table  11 , and the lower air drawing fan  54  that functions as a lower air drawing body. 
     Next, a description is given of operations when the sheet feeding device  200  of  FIG. 11  conveys sheets one by one. 
       FIG. 14  is a flowchart of another sheet feeding operations of the sheet feeding device  200  of  FIG. 11 . 
     The general controller of the image forming apparatus  100  receives an image forming instruction associated with the sheets set in the sheet trays  10  of the sheet feeding device  200  of  FIG. 13  via a control panel of the image forming apparatus  100 . Then, the general controller transmits a sheet feeding instruction to the controller  60  of the sheet feeding device  200  and information of types of sheet loaded on the sheet loading table  11  of the sheet trays  10 . On receipt of the sheet feeding instruction, the controller  60  starts driving the air blowing device  17  while movement of the sheet attraction belt  21  is being stopped. At the same time, the controller  60  starts driving the air drawing fan  61  to start air drawing by the air drawing device  23 . As the air drawing device  23  starts air drawing, the air drawing device  23  generates a negative pressure in the lower area, and a floating uppermost sheet P 1  is attracted to the sheet attraction belt  21 . Further, at the same time, the controller  60  starts driving the lower air drawing fan  54  to start lower air drawing by the lower air drawing fan  54  (step S 21 ). 
     It is to be noted that floating air generated in a floating fan is discharged from the floating nozzle  51  of the front air blowing device  12  and that separation air generated in a separation fan is discharged from the separation nozzle  52  of the front air blowing device  12 . 
     With the above-described operations, the controller  60  prepares the sheet feeding operation (step S 22 ). 
     At this time, the controller  60  causes the shutter valves  42 ,  51   b  and  52   b  to open and the shutter valve  53   b  to close (step S 23 ). Accordingly, as illustrated in  FIG. 11 , air is discharged from the floating nozzle  51  of the front air blowing device  12  in the direction indicted by arrow a 1 . Therefore, the air is blown to the front end part of the upper part of the sheet bundle SB. Further, air is discharged from the air discharging port of the pair of side fences  13  (see  FIG. 4 ) to be blown to the side end of the upper side of the sheet bundle SB. Due to the air discharged and blown through the air discharging ports of the front air blowing device  12  and through the air discharging ports of the pair of side fences  13 , the upper sheet of the sheet bundle SB is lifted to float. Further, air is discharged from the separation nozzle  52  of the front air blowing device  12  in the direction indicted by arrow a 2 . Therefore, the air is blown to the floating uppermost sheet P and the other sheet(s) of the sheet bundle SB. Then, the controller  60  causes the air drawing device  23  to generate a negative pressure in the lower area. 
     Then, the controller  60  determines whether or not the predetermined time (X) has passed from the start of the sheet feeding operation (step S 24 ). When S 24  is NO and the predetermined time has not yet passed, the process repeats step S 24 . When step S 24  is YES and the predetermined time has passed, the sheet P is attracted to the lower face of the sheet attraction belt  21 . Consequently, the controller  60  causes the shutter valves  51   b  and  52   b  to close and the shutter valves  42  and  53   b  to open (step S 25 ). With the above-described operations, the controller  60  completes the preparation of the sheet feeding operation (step S 26 ). 
     Then, as the sheet attraction belt  21  rotates, the sheet feeding operation starts (step S 27 ). Then, the controller  60  determines whether or not the predetermined time (X) has passed from the start of the sheet feeding operation (step S 28 ). When step S 28  is NO and the predetermined time has not yet passed, the process repeats step S 28 . When step S 28  is YES and the predetermined time has passed, the shutter valves  51   b  and  52   b  are open and the shutter valves  42  and  53   b  are closed (step S 29 ). As described above, by performing step S 29  no matter there is a request of the start of the sheet conveying operation or not, the subsequent sheet is floated and separated, so that the sheet attracting and conveying operation can be performed whenever the start of the sheet feeding operation is requested. Accordingly, a high productivity can be obtained. Then, the controller  60  causes the sheet attraction belt  21  to stop (step S 30 ). 
     Then, the controller  60  determines whether or not another instruction of the start of the sheet feeding operation is requested (step S 31 ). When step S 31  is YES and the start of the sheet feeding operation is requested, step S 22  through step S 30  are repeated to convey the subsequent sheet. When step S 31  is NO and the start of the sheet feeding operation is not requested, the sheet attracting and conveying operation is finished, then the controller  60  executes another operation flow after the sheet attracting and conveying operation. 
     Next, a description is given of another operations after completion of the sheet attracting and conveying operation, according to the present embodiment of this disclosure. 
       FIG. 15  is a flowchart of another example of operations after completion of the sheet attracting and conveying operation.  FIG. 16  is a diagram illustrating opening and closing of the shutter valve and movement of the sheet in the sheet feeding device  200 .  FIG. 17  is a diagram illustrating movement of the sheet when the lower air drawing force is increased.  FIG. 18  is a diagram illustrating the movement of the sheet when the sheet loading table is lowered. 
     When the sheet attracting and conveying operation performed by the sheet attracting and conveying device is completed, the controller  60  of  FIG. 13  transmits an instruction to stop the air drawing fan  61 , the floating fan and the separation fan (step S 41 ). The controller  60  causes the lower air drawing fan  54  to continue to drive. At this time, even when the instructions to stop rotation of the air drawing fan  61 , the floating fan and the separation fan are transmitted, air corresponding to the amount of rotation attenuation of each fan are exhausted. Therefore, the operation is adversely affected by the air for a certain period of time. In order to address this inconvenience, as illustrated in  FIG. 16 , the controller  60  transmits the instructions to stop rotation of the air drawing fan  61 , the floating fan and the separation fan and, at the same time, causes the shutter valves  42 ,  51   b  and  52   b.  By so doing, air exhaustion of the air by the amount of rotation attenuation of each fan is blocked. Further, by opening the shutter valve  53   b,  the sheet is encouraged to fall onto the sheet loading table of the sheet tray (step S 42 ). 
     Further, as illustrated in  FIG. 17 , the number of rotations of the lower air drawing fan  54  is more increased than the number of rotations during the sheet feeding operation, so that the lower air drawing force is increased (step S 43 ). Furthermore, as illustrated in  FIG. 18 , the controller  60  causes the sheet loading table to be lowered (step S 44 ). By so doing, the sheet is separated away from the air corresponding to the amount of rotation attenuation of each of the air drawing fan  61 , the floating fan and the separation fan, and therefore the adverse effect due to the air is prevented. Accordingly, the sheet is further encouraged to fall onto the sheet loading table of the sheet tray. In the present embodiment, when the attraction of a sheet by the air drawing is interrupted, the negative pressure in the sheet attracting unit  30  is released simultaneously. Therefore, the sheet can be separated from the sheet attraction belt  21  more quickly. 
     Then, the controller  60  determines whether or not the predetermined time has passed since the shutter valves  42 ,  51   b  and  52   b  are closed (step S 45 ). When S 45  is NO and the predetermined time has not yet passed, the process repeats step S 45 . When step S 45  is YES and the predetermined time has passed, the controller  60  causes the shutter valve  42  to open (step S 46 ). By so doing, when a print job is requested and the air drawing fan  61  starts the sheet attracting operation, the step of opening the shutter valves  42 ,  51   b  and  52   b  can be omitted. Then, the controller  60  causes the lower air drawing fan  54  to turn off (step S 47 ) and turns off the sheet feed working state LED  62  (step S 48 ) simultaneously, so as to indicate a user that the sheet tray  10  is ready to open. 
     As described above, by encouraging the sheet to fall on the sheet loading table by the lower air drawing when the attracting and conveying operation is completed, additional rise and additional attraction of the sheet can be prevented and, at the same time, a waiting time to be ready for pulling out the sheet loading table can be reduced without causing any damage to the sheet when the sheet loading table is pulled out. 
     This configurations according to the above-described embodiments are not limited thereto. This disclosure can achieve the following aspects effectively. 
     Aspect A. 
     In Aspect A, a sheet feeding device such as the sheet feeding device  200  includes a sheet loader such as the sheet loading table  11 , an air drawing body such as the air drawing fan  61 , and an attracting and conveying device such as the sheet attraction belt  21  and the air drawing device  23 . The sheet loader is a device on which a bundle of sheets is loaded. The air drawing body is configured to generate suction air. The attracting and conveying device is configured to attract an uppermost sheet on the bundle of sheets by the air drawing body and convey the attracted sheet. The attracting and conveying device includes a sheet attracting portion such as the sheet attracting unit  30  configured to attract the uppermost sheet, an air duct such as the air duct  41  configured to intake the suction air to the sheet attracting portion, a blocking device such as the shutter valve  42  configured to block the suction air in the air duct, and a controller such as the controller  60  configured to control a shutdown operation of the suction air. The controller is configured to shut down the suction air at completion of conveyance of the uppermost sheet by the attracting and conveying device. 
     In Aspect A, the blocking device shuts down the suction air at completion of conveyance of the sheet. Therefore, at completion of conveyance of the sheet, the suction air can be blocked by the blocking device at the same time when the air drawing body is stopped. According to this configuration, when compared with a comparative sheet feeding device that does not include the blocking device, attraction of the sheet with the suction air during the stop of operation of the air drawing body can be shut down quickly. Therefore, the time that the sheet attracted to the attracting and conveying device is separated from the attracting and conveying device can be reduced. Accordingly, the waiting time to be ready for pulling out the sheet loader can be reduced without causing any damage to the sheet when the sheet loader is pulled out. 
     Aspect B. 
     The sheet feeding device according to Aspect A further includes a working state indicator such as the sheet feed working state LED  62  configured to indicate a working state of the sheet feeding device. At a time that a set time has passed since the suction air in the air duct such as the air duct  41  is shut down by the blocking device such as the shutter valve  42 , the controller such as the controller  60  causes the working state indicator to indicate that the sheet feeding device is not under operation. 
     In Aspect B, as described in the above-described embodiment, a user can be prevented from touching a heated solenoid such as the solenoid  43 , and therefore can be safe. 
     Aspect C. 
     The sheet feeding device according to Aspect A or Aspect B further includes a loader elevation device such as the elevation drive motor  19  configured to lift and lower the sheet loader, a plate configured to regulate a leading end position of the bundle of sheets in a sheet conveying direction, a floating air blower such as the front air blowing device  12  configured to blow air from the leading end position of the bundle of sheets and cause the sheet to float, and a separating air blower such as the front air blowing device  12  configured to blow air to the leading end of sheets floated by the floating air blower and cause the sheets to be separated one by one. The sheet attracting and conveying device such as the sheet attraction belt  21  and the air drawing device  23  is configured to attract an uppermost sheet of the sheets floated by the floating air blower and convey the uppermost sheet. The blocking device such as the shutter valve  42  uses a solenoid such as the solenoid  43  and a tension spring to shut down the suction air in the air duct such as the air duct  4 L The controller such as the controller  60  causes the suction air to be shut down by the blocking device via the solenoid. 
     Aspect D. 
     In the sheet feeding device according to any one of Aspect A through Aspect C, the air duct includes a wall having a leak hole such as the leak hole  44  that goes through an inside and an outside of the air duct. When the suction air is blocked by the blocking device such as the shutter valve  42 , the leak hole becomes open. 
     In Aspect D, as described in the above-described embodiments, the sheet can be peeled off or separated from the sheet attracting belt that functions as the attracting and conveying device more quickly. Accordingly, at completion of the sheet attracting and conveying operation, the sheet attracted to the sheet attracting and conveying device can be returned to the sheet loader quickly. 
     Aspect E. 
     In the sheet feeding device according to Aspect D, when the suction air is not blocked by the blocking device such as the shutter valve  42 , the leak hole such as the leak hole  44  is closed by the blocking device. By contrast, when the suction air is blocked by the blocking device, the leak hole is opened by the blocking device. 
     In Aspect E, by switching the dosing and opening of the leak hole by the blocking device, no mechanism dedicated to the closing and opening of the leak hole needs to be provided. 
     Aspect F. 
     The sheet feeding device according to Aspect A further includes a lower air drawing body configured to attract the sheet by a lower suction air directing to the sheet loader, a lower air drawing air duct such as the air duct  53   a  through which the lower suction air drawn by the lower air drawing body passes, and a lower suction air opening and closing device such as the shutter valve  53   b  configured to block and open the lower suction air in the lower air drawing air duct. The controller such as the controller  60  is configured to release the lower suction air in the lower air drawing air duct by the lower suction air opening and closing device, at completion of conveyance of the uppermost sheet by the attracting and conveying device. 
     In Aspect F, as described in the above-described embodiments, the sheet can be peeled off or separated from the sheet attracting belt more quickly. Accordingly, at completion of the sheet attracting and conveying operation, the sheet attracted to the sheet attracting and conveying device can be returned to the sheet loader quickly. 
     Aspect G. 
     In the sheet feeding device according to Aspect F, the controller increases an air drawing force applied by the lower air drawing body at completion of conveyance of the sheet by the attracting and conveying device. 
     In Aspect G, as described in the above-described embodiments, the sheet can be encouraged to fall onto the sheet loader. 
     Aspect H. 
     In the sheet feeding device according to Aspect F or Aspect G, the controller causes the sheet loader to be lowered at completion of conveyance of the sheet by the attracting and conveying device. 
     In Aspect H, as described in the above-described embodiments, the sheet loader is lowered to separate the sheet away from the suction air. Therefore, a negative impact by the air can be prevented. Therefore, the sheet can be encouraged to fall onto the sheet loader. 
     Aspect I. 
     In Aspect I, an image forming apparatus includes an image forming device to form an image on a surface of a sheet, and the sheet feeding device according to any one of Aspect A through Aspect H to feed the sheet to the image forming device. 
     In Aspect I, the image forming apparatus, in which the waiting time to be ready for pulling out the sheet loader can be reduced without causing any damage to the sheet when the sheet loader is pulled out, can be provided. 
     Aspect J. 
     In Aspect J, an image forming system includes at least an image forming apparatus including an image forming device to form an image on a surface, and the sheet feeding device according to any one of sheet feeding device according to any one of Aspect A through Aspect G to feed the sheet to the image forming device. 
     In Aspect J, the image forming system, in which the waiting time to be ready for pulling out the sheet loader can be reduced without causing any damage to the sheet when the sheet loader is pulled out, can be provided. 
     The above-described embodiments are illustrative and do not limit this disclosure. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements at least one of features of different illustrative and exemplary embodiments herein may be combined with each other at least one of substituted for each other within the scope of this disclosure and appended claims. Further, features of components of the embodiments, such as the number, the position, and the shape are not limited the embodiments and thus may be preferably set. It is therefore to be understood that within the scope of the appended claims, the disclosure of this disclosure may be practiced otherwise than as specifically described herein.