Patent Publication Number: US-9417586-B2

Title: Sheet discharge device and image forming apparatus including the same

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2014-038079 filed on Feb. 28, 2014, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a sheet discharge device for discharging a sheet from a sheet discharge port onto a sheet discharge tray, and to an image forming apparatus including the sheet discharge device. 
     A conventional image forming apparatus includes a full-stack detection mechanism that detects whether or not the amount of sheets stacked on a sheet discharge tray is equal to or larger than a predetermined amount, in order to prevent a sheet discharge port from being closed by the discharged sheets. The full-stack detection mechanism detects whether or not the amount of a stack of sheets on the sheet discharge tray has reached the predetermined amount, by determining whether or not the height of the stack of sheets on the sheet discharge tray has reached a predetermined full-stack detection height. 
     SUMMARY 
     A sheet discharge device according to an aspect of the present disclosure includes a discharge roller, a detection portion, and a detection position changing mechanism. The discharge roller is configured to discharge a sheet from a sheet discharge port toward a sheet discharge tray. The detection portion is configured to detect that a stack height of sheets on the sheet discharge tray has reached a predetermined detection position. The detection position changing mechanism is configured to change the detection position for the detection portion. 
     An image forming apparatus according to another aspect of the present disclosure includes the sheet discharge device. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an image forming apparatus in the first embodiment of the present disclosure. 
         FIG. 2  is a schematic diagram showing the internal configuration of the image forming apparatus of  FIG. 1 . 
         FIG. 3  is a perspective view showing a sheet discharge device in the first embodiment of the present disclosure. 
         FIG. 4  is a partially enlarged view of the main portions of  FIG. 3 . 
         FIG. 5  is a cross section of the sheet discharge device of  FIG. 3 . 
         FIG. 6  is a perspective view showing a detection position changing mechanism provided in the sheet discharge device of  FIG. 3 . 
         FIGS. 7A and 7B  are diagrams showing the attachment states of a detection member. 
         FIG. 8  is a cross section showing an image forming apparatus in the second embodiment of the present disclosure. 
         FIG. 9  is a diagram showing a detection position changing mechanism provided in the sheet discharge device of  FIG. 8 . 
         FIGS. 10A through 10C  are diagrams showing a detection position changing mechanism provided in the sheet discharge device of  FIG. 8 . 
         FIGS. 11A through 11C  are diagrams showing a detection position changing mechanism provided in the sheet discharge device in the third embodiment of the present disclosure. 
         FIGS. 12A through 12C  are diagrams showing a detection position changing mechanism provided in the sheet discharge device in the fourth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     [First Embodiment] 
     The following describes, with reference to the drawings, a sheet discharge device  60  according to the first embodiment of the present disclosure and an image forming apparatus  10  including the sheet discharge device  60 . It is noted that for the sake of explanation, an up-down direction  6  is defined as the vertical direction in the state (the state shown in  FIG. 1 ) where the image forming apparatus  10  is installed on a flat surface. In addition, a front-rear direction  7  is defined on the supposition that a surface on which an operation display panel  17  is provided is the front surface (front side). Furthermore, a left-right direction  8  is defined based on the front surface of the image forming apparatus  10 . It is noted that embodiments described in the following are merely concrete examples of the present disclosure, and are not intended to limit the technical scope of the present disclosure. 
     First, the configuration of the image forming apparatus  10  will be described with reference to  FIGS. 1 and 2 . As shown in  FIG. 1 , the image forming apparatus  10  is a so-called “in-body discharge type” multifunction peripheral, and has various functions such as a printer, a copier, a facsimile, a scanner, and the like. The image forming apparatus  10  forms an image of an input image onto a print sheet P (an example of the sheet of the present disclosure) by using a print material such as toner. Note that the image forming apparatus  10  is not limited to a multifunction peripheral, and the present disclosure is also applicable to a specialized device such as a printer, a copier, a facsimile, a scanner provided with an ADF  13 , or the like. 
     The image forming apparatus  10  includes an image reading portion  12  and an image forming portion  14 . The image reading portion  12  performs the process of reading an image from a document sheet, and is provided in the upper part of the image forming apparatus  10 . The image forming portion  14  performs the process of forming an image based on the electrophotography, and is provided below the image reading portion  12 . The image forming portion  14  includes two sheet feed devices  27  and  28  that are arranged as two tiers in the vertical direction. The sheet feed device  27 , the upper one of the two sheet feed devices, is integrally formed with a housing  29  at the lowest part of the image forming portion  14 . The sheet feed device  28 , the lower one of the two sheet feed devices, is extension-type and is attached to the bottom surface of the housing  29  of the image forming portion  14  as an option device. The sheet feed device  28  is configured to be attachable/dechable to/from the bottom surface of the housing  29 . In addition, a paper sheet discharge portion  30  is provided in the right side of the image forming portion  14 . It is noted that the image forming method of the image forming portion  14  is not limited to the electrophotography, but may be an inkjet recording method or other recording or printing methods. 
     Above the image forming portion  14 , there is provided a sheet discharge space  21  to which print sheets P are discharged. The paper sheet discharge portion  30  is formed in such a way as to couple the image forming portion  14  with the image reading portion  12  with the sheet discharge space  21  provided therebetween. As shown in  FIG. 1 , the front side and the left side of the sheet discharge space  21  are opened, while the rear side and the right side thereof are not opened. Specifically, the rear side is closed, and in the right side, the paper sheet discharge portion  30  is provided. In the sheet discharge space  21 , a sheet discharge tray  21 A (an example of the sheet discharge tray of the present disclosure) for holding discharged print sheets P in a stacked manner is provided. In the present embodiment, the sheet discharge device  60  is provided in the paper sheet discharge portion  30 . 
     The sheet discharge tray  21 A is configured to hold a plurality of discharged print sheets P thereon in a stacked manner, and is provided on the upper surface of the image forming portion  14 . The sheet discharge tray  21 A is formed from ABS resin by the injection molding. A paper sheet holding surface, namely the upper surface of the sheet discharge tray  21 A has a plurality of ribs  44  (see  FIG. 3 ). The ribs  44  extend in the same direction as the discharge direction of the print sheet P (the left-right direction  8 ). It is noted that the material of the sheet discharge tray  21 A is not limited to the ABS resin, but may be a synthetic resin other than the ABS resin. 
     As shown in  FIG. 1 , the image reading portion  12  includes a document sheet placing table  23 . When the image forming apparatus  10  functions as a copier, a document sheet is set on the document sheet placing table  23 , and after a document sheet cover  24  (see  FIG. 2 ) is closed, a copy start instruction is input from an operation display panel  17 . This causes the image reading portion  12  to start the reading operation to read image data from the document sheet. The read image data is sent to the image forming portion  14 . It is noted that in  FIG. 1 , the document sheet cover  24  (see  FIG. 2 ) of the image reading portion  12  is omitted. 
     In addition, as shown in  FIG. 2 , the image reading portion  12  includes an ADF  13 . The ADF  13  is provided in the document sheet cover  24 . The ADF  13  is an automatic document sheet feeding device and includes a document sheet tray  45 , a feeding mechanism  46 , a plurality of conveying rollers  47 , a paper sheet pressing  48 , a sheet discharge portion  49 , and the like. The ADF  13  drives the feeding mechanism  46  and the conveying rollers  47  by motors (not shown) respectively to feed a document sheet set on the document sheet tray  45  such that the document sheet is conveyed to the sheet discharge portion  49  after passing a reading position  43  on the document sheet placing table  23 . The feeding mechanism  46  includes a pick-up roller  46 A for picking up a document sheet and a feeding roller  46 B for feeding the document sheet picked up by the pick-up roller  46 A. A document sheet is picked up by the pick-up roller  46 A from the document sheet tray  45  and fed by the feeding roller  46 B toward the downstream side in the feeding direction. The document sheet is further conveyed by a conveying roller  47  that is provided in the downstream side in the feeding direction. The image reading portion  12  reads the image from the document sheet at the reading position  43  when the document sheet conveyed by the ADF  13  passes the reading position  43 . 
     The image forming portion  14  forms an image on a print sheet P based on the image data which has been read by the image reading portion  12  or input from the outside, wherein the print sheet P has a specific size such as an A series size or a B series size. The image forming portion  14  performs a single side print process (single side image forming process) or a double side print process (double side image forming process) based on a print mode (a single side print mode or a double side print mode) which is set in advance. In the single side print process, an image is formed on a side of a print sheet P; and in the double side print process, images are formed on both of opposite sides of a print sheet P. During the single side print process, the image forming portion  14  discharges the print sheet P with an image formed on one side thereof onto the sheet discharge tray  21 A of the sheet discharge space  21 . On the other hand, during the double side print process, the image forming portion  14  switches back a print sheet P with an image formed on one side thereof, sends it into a reverse conveyance path  39 , forms an image on the reverse side of the print sheet P as well, and then discharges the print sheet P with images formed on both sides into the sheet discharge tray  21 A of the sheet discharge space  21 . 
     As shown in  FIG. 2 , the image forming portion  14  mainly includes the sheet feed devices  27 ,  28 , an electrophotographic image transfer portion  18 , a fixing portion  19 , the sheet discharge device  60 , a control portion (not shown) for comprehensively controlling the image forming portion  14 , and the like. That is, the image forming apparatus  10  includes the sheet discharge device  60 . In addition, the image forming portion  14  includes a conveyance motor and a discharge motor (both not shown). These portions are provided inside the housing  29  that constitutes the outer frame cover, the internal frame and the like of the image forming portion  14 . 
     The sheet feed devices  27 ,  28  convey a print sheet P toward the image transfer portion  18 . Each of the sheet feed devices  27  and  28  includes: a paper sheet storing portion  22  in the shape of a tray; and a feeding mechanism  15 . In the paper sheet storing portion  22 , print sheets P (print sheets P used for image formation) on which images are to be formed by the image transfer portion  18  are stored in a stacked manner. The feeding mechanism  15  picks up and conveys, one by one, the print sheets P stored in the paper sheet storing portion  22 . The feeding mechanism  15  is provided above the right end of the paper sheet storing portion  22 . The feeding mechanism  15  includes a pick-up roller  51  and a pair of feeding rollers  52 . When an instruction to feed a print sheet P is input to the image forming apparatus  10 , the conveyance motor is rotationally driven. This allows the pick-up roller  51  and the pair of feeding rollers  52  to rotate. The pick-up roller  51  then picks up a print sheet P from the sheet storing portion  22 , and the print sheet P is fed by the pair of feeding rollers  52  toward the downstream side in the feeding direction. 
     As shown in  FIG. 2 , in the image forming portion  14 , a conveyance path  26  is formed to extend upward from the pair of feeding rollers  52  of the sheet feed device  28 . The conveyance path  26  is formed in the right-side part of the housing  29 . The conveyance path  26  extends in the up-down direction  6  along the right side surface, and reaches a paper sheet discharge port  37  (an example of the sheet discharge port of the present disclosure) via the fixing portion  19 . 
     The image transfer portion  18  is provided above the sheet feed device  27 . The image transfer portion  18  performs an image transfer process onto the print sheet P conveyed from the sheet feed devices  27 ,  28 . Specifically, the image transfer portion  18  transfers a toner image onto a print sheet P based on the input image data, using a print material such as toner. As shown in  FIG. 2 , the image transfer portion  18  includes a photoconductor drum  31 , a charging portion  32 , a developing portion  33 , an LSU (Laser Scanning Unit)  34 , a transfer roller  35 , and a cleaning portion  36 . 
     The photoconductor drum  31  is provided in the left side of the conveyance path  26 . When the image forming operation is started, the charging portion  32  charges the surface of the photoconductor drum  31  uniformly into a certain potential. In addition, the LSU  34  scans the photoconductor drum  31  with laser light based on the image data. This allows an electrostatic latent image to be formed on the photoconductor drum  31 . Subsequently, the developing portion  33  causes the toner to adhere to the electrostatic latent image, and a toner image is formed on the photoconductor drum  31 . The transfer roller  35  is provided in the right side of the conveyance path  26 , and is disposed to face the photoconductor drum  31  across the conveyance path  26 . When the print sheet P conveyed in the conveyance path  26  passes through a nip portion between the transfer roller  35  and the photoconductor drum  31 , the toner image is transferred onto the print sheet P by the transfer roller  35 . The print sheet P with the toner image transferred thereon is conveyed in the conveyance path  26  to the fixing portion  19  that is disposed in the downstream side of (i.e., above) the image transfer portion  18  in the conveyance direction of the print sheet P. 
     The fixing portion  19  fixes the transferred toner image on the print sheet P to the print sheet P by heat. The fixing portion  19  includes a heating roller  41  and a pressure roller  42 . The pressure roller  42  is biased toward the heating roller  41  by an elastic member such as a spring. As a result, the pressure roller  42  is brought into pressure contact with the heating roller  41 . During the fixing operation, the heating roller  41  is heated to a high temperature by a heating device (not shown) such as a heater. When the print sheet P passes through the fixing portion  19 , the toner forming the toner image is heated and fused by the heating roller  41 , and the print sheet P is pressed by the pressure roller  42 . This allows the toner to be fixed to the print sheet P by the fixing portion  19 . That is, the toner image is fixed to the print sheet P, and an image is formed on the print sheet P. After the fixing, the print sheet P is conveyed in the conveyance path  26  from the fixing portion  19  to the paper sheet discharge port  37  by the rollers  41  and  42  of the fixing portion  19 . 
     The sheet discharge device  60  is provided above the fixing portion  19 . The sheet discharge device  60  is provided inside the paper sheet discharge portion  30 . As shown in  FIG. 3 , the sheet discharge device  60  includes pairs of discharge rollers  25 , a sheet amount detecting mechanism  70  (an example of the detection portion of the present disclosure), and a detection position changing mechanism  80 . 
     The pairs of discharge rollers  25  are provided near the paper sheet discharge port  37 . Each pair of discharge rollers  25  is composed of a driving roller  25 A and a driven roller  25 B, wherein the driving roller  25 A is rotationally driven by a motor, and the driven roller  25 B is pressed against the driving roller  25 A. A plurality of pairs of discharge rollers  25  are disposed along the front-rear direction  7  of the image forming apparatus  10 . The pairs of discharge rollers  25  are configured to discharge the print sheet P from the paper sheet discharge port  37  onto the sheet discharge tray  21 A. After passing through the fixing portion  19 , the print sheet P is conveyed upward in the conveyance path  26 . The conveyance path then changes its direction from the vertical direction to the horizontal direction, and guides the print sheet P to the paper sheet discharge port  37 . When the front end of the print sheet P reaches the nip portion of the pairs of discharge rollers  25 , the print sheet P is conveyed toward the sheet discharge tray  21 A while being nipped by the pairs of discharge rollers  25 . 
     The sheet amount detecting mechanism  70  is provided in the downstream side of the pairs of discharge rollers  25 . The sheet amount detecting mechanism  70  is configured to detect that the stack height of the sheets on the sheet discharge tray  21 A has reached a predetermined detection position. As shown in  FIGS. 4 and 5 , the sheet amount detecting mechanism  70  includes arm-like detection members  71  (an example of the first pivoting body of the present disclosure), a pivoting shaft  72 , a light blocking plate  73  (an example of the second pivoting body of the present disclosure), and an optical sensor  74  (an example of the sensor of the present disclosure). 
     The detection members  71  pivot to a position which corresponds to the stack height of a stack of sheets on the sheet discharge tray  21 A. Specifically, the detection members  71  are attached to the pivoting shaft  72  that is provided above the paper sheet discharge port  37 . The detection members  71  each extend in a radial direction of the pivoting shaft  72 . The pivoting shaft  72  is pivotably supported by side frames  61  and  62  that are provided at opposite ends of the sheet discharge device  60  in the front-rear direction  7 . In the present embodiment, three detection members  71  are fixed to the pivoting shaft  72 . The three detection members  71  are disposed in the rear of the center of the pivoting shaft  72 . A detection member  71  in the most rear side is disposed at such a position to be able to contact a discharged paper sheet of the largest size (for example, A3 size). A detection member  71  that is closest to the center of the pivoting shaft  72  is disposed at such a position to be able to contact a discharged paper sheet of the smallest size (for example, A5 size). With this configuration, when a print sheet P is discharged from the paper sheet discharge port  37 , one or more detection members  71  pivot. In addition, after a print sheet P is completely discharged from the paper sheet discharge port  37  and stacked on the sheet discharge tray  21 A, the upper surface of the print sheets P stacked on the sheet discharge tray  21 A abuts on the detection members  71  and raises the detection members  71  upward. In this way, the detection members  71  pivot around the pivoting shaft  72  and are displaced to a position corresponding to the stack height of the stack of print sheets P. 
     The light blocking plate  73  is fixed to the rear end of the pivoting shaft  72 . The light blocking plate  73  extends in a radial direction of the pivoting shaft  72 . Upon receiving a rotational force for a rotation in the pivoting direction that is transmitted from the detection members  71  via the pivoting shaft  72 , the light blocking plate  73  pivots in the same pivoting direction in conjunction with the pivoting of the detection members  71 . Based on the pivoting of the detection members  71 , the light blocking plate  73  reciprocates between a light-blocking position and a non-light-blocking position, wherein at the light-blocking position, the light blocking plate  73  blocks the detection light path of the optical sensor  74 , and at the non-light-blocking position, the light blocking plate  73  is off the detection light path. In the present embodiment, when no print sheet P is discharged and no print sheet P is stacked on the sheet discharge tray  21 A, the light blocking plate  73  is disposed at the light-blocking position, supported by a stopper member (not shown), wherein the light-blocking position is the movement lower-limit of the light blocking plate  73 . 
     The optical sensor  74  is a sensor configured to detect that the light blocking plate  73  has reached the non-light-blocking position. The optical sensor  74  of the present embodiment is a photointerrupter that includes a light emitter such as an LED light emitting element and a light receptor such as a phototransistor. The optical sensor  74  is a transmission-type photointerrupter in which the light emitter and the light receptor are disposed to face each other across a space. The light emitter emits detection light and the light receptor receives the detection light, and when the light blocking plate  73  is disposed in the detection light path between the light emitter and the light receptor, the light path is interrupted, and the output signal of the optical sensor  74  changes from a HIGH level to a LOW level. On the other hand, when the light blocking plate  73  moves upward from the light-blocking position and is off the detection light path, the output signal of the optical sensor  74  changes from the LOW level to the HIGH level. When the output signal of the optical sensor  74  changes from the LOW level to the HIGH level, the optical sensor  74  detects that the amount of print sheets P stacked on the sheet discharge tray  21 A has reached a predetermined set amount. 
     Meanwhile, various types of sheets are distributed in the market, and the print sheets P can be various in type. As a result, the stack form of print sheets P on the sheet discharge tray  21 A varies depending on the type of the sheets. For example, depending on the material and thickness of the sheets, ends of the discharged sheets may be curled or curved. In this way, the stack form changes depending on the shape of the sheets. In addition, depending on the type of discharged sheets, the detection position with respect to the stack height of the sheets on the sheet discharge tray  21 A may be desired to be higher or lower than the initial setting height. For example, in a case where sheets having low heat radiation are used and discharged after being heated during the image formation, the detection position of the stack height is desired to be lower than the initial setting height so that the heat accumulated in the stacked sheets does not adversely affect any other parts. However, conventional full stack detection mechanisms cannot change the detection position from a predetermined initial setting height to detect the stack height of the sheets on the sheet discharge tray  21 A. On the other hand, according to the present embodiment, a detection position changing mechanism  80  that is described below is provided, and thus the detection position of the stack height of the sheets on the sheet discharge tray  21 A can be set to an arbitrary position. 
     The detection position changing mechanism  80  allows for change of the detection position for the detection by the sheet amount detecting mechanism  70 . The detection position changing mechanism  80  is provided on the pivoting shaft  72 . In the present embodiment, the pivoting shaft  72  is divided into a pivoting shaft  72 A (first pivoting shaft) and a pivoting shaft  72 B (second pivoting shaft), wherein the pivoting shaft  72 A pivotably supports the detection members  71 , and the pivoting shaft  72 B pivotably supports the light blocking plate  73 . The detection position changing mechanism  80  is configured as a coupling (an example of the shaft coupling portion of the present disclosure) that allows the pivoting shaft  72 A to be coupled with the pivoting shaft  72 B and releases that coupling. In the present embodiment, the detection position changing mechanism  80  can be used to adjust the angle made by the detection members  71  and the light blocking plate  73 . 
     As shown in  FIG. 6 , the detection position changing mechanism  80  includes shaft couplings  81  and  82 , wherein the shaft coupling  81  is fixed to an end of the pivoting shaft  72 A, and the shaft coupling  82  is fixed to an end of the pivoting shaft  72 B. The shaft couplings  81  and  82  are configured in such a way as to be coupled with and released from each other. Specifically, the shaft coupling  81  includes a plurality of grooves  81 A provided at equal intervals along the circumferential direction. Each of the grooves  81 A extends, with a narrow width, long in the axis direction of the pivoting shaft  72 A. The shaft coupling  82  includes a plurality of projections  82 A provided at equal intervals along the circumferential direction. Each of the projections  82 A extends, with a narrow width, long in the axis direction of the pivoting shaft  72 B and is formed with such a size and at such a position as to be inserted into a corresponding groove among the plurality of grooves  81 A. The shaft coupling  81  and the shaft coupling  82  are coupled with each other when the plurality of projections  82 A are respectively inserted into the plurality of grooves  81 A. With this configuration, it is possible to change the coupling position of the shaft couplings  81  and  82  in the circumferential direction to an arbitrary rotational position. That is, the angle made by the detection members  71  and the light blocking plate  73  can be adjusted arbitrarily. Specifically, the shaft coupling  81  is temporarily removed from the shaft coupling  82 , and then the shaft coupling  81  is coupled with the shaft coupling  82  again after it is rotated in the circumferential direction. In this way, the coupling position of the shaft couplings  81  and  82  in the circumferential direction is changed to an arbitrary rotatational position. 
     Next, a description is given of the print sheet P discharging operation in the sheet discharge device  60 . In the initial state where no print sheet P is discharged onto the sheet discharge tray  21 A and no print sheet P is stacked on the sheet discharge tray  21 A, the light blocking plate  73  is disposed at the light-blocking position, and the detection members  71  are inclined downward and stand still by its self weight (see  FIG. 5 ). In this state, when a print sheet P is discharged from the paper sheet discharge port  37  by the pairs of discharge rollers  25 , the front end of the print sheet P abuts on the detection members  71  and is discharged toward the sheet discharge space  21  while allowing the detection members  71  to pivot toward the discharge direction. When the rear end of the print sheet P passes the detection members  71  attachment position (the pivoting shaft  72 A) and the print sheet P is stacked on the sheet discharge tray  21 A, the detection members  71  return to the original positions, and the light blocking plate  73  returns from the non-light-blocking position to the light-blocking position. 
     As the above-described operation is performed each time a print sheet P is discharged, a plurality of print sheets P are stacked on the sheet discharge tray  21 A. As the stack amount of print sheets P increases gradually, the detection members  71  supported by the top surface of the stacked print sheets P are gradually displaced upward. Subsequently, when the stack amount of print sheets P reaches a predetermined set amount, the detection members  71  are at such a position that allows the light blocking plate  73  to stay at the non-light-blocking position even when the rear end of the print sheet P passes the detection members  71  attachment position (the pivoting shaft  72 A). At this time, the output signal of the optical sensor  74  always maintains the HIGH level. When the HIGH level is maintained for a predetermined time period, the control portion (not shown) determines that the stack amount of print sheets P on the sheet discharge tray  21 A has reached the predetermined set amount. 
     In the present embodiment, the above-described detection position changing mechanism  80  is provided in the sheet discharge device  60 . This makes it possible to set the detection position for detection of the stack height of print sheets P on the sheet discharge tray  21 A, to an arbitrary position. Specifically, the detection position changing mechanism  80  can be adjusted to an arbitrary position to change the inclination angle of the detection members  71  with respect to the vertical direction in the initial state. For example, as shown in  FIG. 7A , the inclination angle of the detection members  71  can be made larger than the inclination angle shown in  FIG. 5 . In that case, the distance between the detection members  71  and the sheet discharge tray  21 A in the initial state is increased. This increases the stack amount required for the detection members  71  to be displaced to the position where the light blocking plate  73  stays at the non-light-blocking position. Furthermore, as shown in  FIG. 7B , the inclination angle of the detection members  71  can be made larger than the inclination angle shown in  FIG. 7A . In that case, the distance between the detection members  71  and the sheet discharge tray  21 A in the initial state is further increased. This further increases the stack amount required for the detection members  71  to be displaced to the position where the light blocking plate  73  stays at the non-light-blocking position. 
     [Second Embodiment] 
     The following describes, with reference to  FIGS. 8 through 10 , the second embodiment of the present disclusure. In the second embodiment, a reflection-type optical sensor  90  (an example of the detection portion of the present disclosure) is used to detect the amount of sheets, in place of the sheet amount detecting mechanism  70  described in the first embodiment. In addition, a detection position changing mechanism  100  is used in place of the detection position changing mechanism  80 . 
     As shown in  FIG. 8 , the optical sensor  90  is a reflection-type sensor which is configured to emit light to the side surface of a stack of sheets on the sheet discharge tray  21 A and receive reflected light therefrom. Specifically, the optical sensor  90  is a reflection-type photointerrupter. The optical sensor  90  is attached to the internal frame of the paper sheet discharge portion  30  via a support bracket  92 , below the paper sheet discharge port  37  and above the upper surface of the sheet discharge tray  21 A. When the amount of print sheets P stacked on the sheet discharge tray  21 A is smaller than the set amount, the optical sensor  90  does not receive the reflected light and outputs a signal of a LOW level. On the other hand, when the amount of print sheets P stacked on the sheet discharge tray  21 A is equal to or larger than the set amount, the optical sensor  90  receives the reflected light and outputs a signal of a HIGH level. When the output signal of the optical sensor  90  changes from the LOW level to the HIGH level, the control portion (not shown) determines that the stack amount of print sheets P on the sheet discharge tray  21 A has reached the predetermined set amount. 
     The detection position changing mechanism  100  changes the position of the light spot on the side surface of the stack of print sheets P, the light spot being made by the light emitted from the optical sensor  90 . Specifically, the detection position changing mechanism  100  allows the optical sensor  90  to pivot to change the light emission angle such that the light spot shifts in the height direction of the stack of print sheets P (a direction perpendicular to the upper surface of the sheet discharge tray  21 A). As shown in  FIG. 9 , the detection position changing mechanism  100  includes a support bracket  92  (an example of the sensor supporting portion of the present disclosure), an adjustment shaft  101 , and an operation dial  102 . The adjustment shaft  101  and the operation dial  102  are an example of the operation portion of the present disclosure. The optical sensor  90  is fixed to the support bracket  92 . The support bracket  92  is supported by the internal frame of the paper sheet discharge portion  30  in such a way as to be able to pivot around the pivoting shaft  93  that extends in the front-rear direction  7 . This allows the support bracket  92  to support the optical sensor  90  in such a way as to be able to pivot in a rotational direction (predetermined direction) around the pivoting shaft  93 . The adjustment shaft  101  is provided for the adjustment of the position of the optical sensor  90 , and is coupled with the support bracket  92  of the optical sensor  90 . Specifically, the adjustment shaft  101  is coupled with the pivoting shaft  93  of the support bracket  92  and extends frontward from the coupling portion. The operation dial  102  is coupled with the front end of the adjustment shaft  101 . A scale indicator (not shown) such as a rotation angle scale is provided on the operation dial  102 , wherein the scale indicator is formed in such a way as to indicate the pivoting position of the optical sensor  90 . The scale indicator is provided on a side surface of the operation dial  102 . 
       FIG. 10A  shows the reference attitude of the optical sensor  90 . When the operation dial  102  is rotated counterclockwise from the reference attitude, the optical sensor  90  pivots around the pivoting shaft  93  and the light emission direction is shifted downward (see  FIG. 10B ). With this operation, the light spot on the side surface of the stack of print sheets P is shifted downward. By shifting the light spot downward, it is possible to reduce the stack amount (set amount) of print sheets P that is required to receive the reflected light. In addition, when the operation dial  102  is rotated clockwise from the reference attitude, the optical sensor  90  also pivots around the pivoting shaft  93  and the light emission direction is shifted upward (see  FIG. 10C ). With this operation, the light spot on the side surface of the stack of print sheets P is shifted upward. By shifting the light spot upward, it is possible to increase the stack amount (set amount) of print sheets P that is required to receive the reflected light. Furthermore, since the scale indicator is provided on the operation dial  102 , the user can recognize the rotation amount of the optical sensor  90  when he/she rotationally operates the operation dial  102 . This enables the user to recognize the stack amount of print sheets P before and after the operation. 
     [Third Embodiment] 
       FIGS. 11A through 11C  shows the third embodiment of the present disclosure in which a cam driving mechanism  105  is applied to the mechanism for allowing the support bracket  92  to pivot in the detection position changing mechanism  100  of the second embodiment. As shown in  FIGS. 11A through 11C , in the cam driving mechanism  105  adopted in the third embodiment, the adjustment shaft  101  is not coupled with the pivoting shaft  93 , but is coupled with a pivoting shaft  107  of an eccentric cam  106  that is abutting on the bottom surface of the support bracket  92 . Even with this configuration, it is possible, with operation of the operation dial  102 , to shift the light spot made by the light emitted from the optical sensor  90 , on the side surface of the stack of print sheets P. 
     [Fourth Embodiment] 
       FIGS. 12A through 12C  shows the fourth embodiment of the present disclosure to which is applied, in place of the mechanism in the detection position changing mechanism  100  of the third embodiment for allowing the support bracket  92  to pivot, a mechanism that uses the cam driving mechanism  105  to move the support bracket  92  in the height direction of the stack of print sheets P. As shown in  FIGS. 12A through 12C , according to the configuration adopted in the fourth embodiment, the adjustment shaft  101  is not coupled with the pivoting shaft  93 , but is coupled with the pivoting shaft  107  of the eccentric cam  106  that is abutting on the bottom surface of the support bracket  92 . In addition, the optical sensor  90  is fixed to the support bracket  92 , and the support bracket  92  is supported by the internal frame of the paper sheet discharge portion  30  in such a way as to be able to move in the height direction of the stack of print sheets P. With the detection position changing mechanism  100  configured as such, it is possible, with operation of the operation dial  102 , to move the optical sensor  90  in the height direction of the stack of sheets and shift the light emission position in the height direction of the stack of sheets. That is, it is possible to shift, in the height direction of the stack of sheets, the position of the light spot made by the light emitted from the optical sensor  90 , on the side surface of the stack of print sheets P. 
     The above-described embodiments describe the sheet discharge device  60  in which the print sheets P are discharged from the image forming portion  14 . However, the present disclosure is not limited to this configuration. For example, the present disclosure is applicable to a mechanism of the ADF  13  in which a document sheet is discharged to the sheet discharge portion  49  by the conveying rollers  47 . 
     It is to be understood that the embodiments herein are illustrative and not restrictive, since the scope of the disclosure is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.