Patent Publication Number: US-2018052412-A1

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     Technical Field 
     The present invention relates to an image forming apparatus, and more specifically relates to an image forming apparatus such as a printer that can determine various sizes of a recording medium such as paper. 
     Related Art 
     Conventionally, image forming apparatuses such as those in patent documents 1 and 2, for example, are known as an image forming apparatus equipped with a size determining mechanism that can determine various sizes of a recording medium mounted on a mounting portion. 
     In patent document 1, an automatic document feeding device for an image forming apparatus equipped with a document detection sensor is disclosed. The document detection sensor is a reflective type optical sensor having a light emitter and a light receiving part, and the document detection sensor is configured so as to detect the document via a detection hole from below or inside a document feeding table. 
     Furthermore, in patent document 2, an image forming apparatus having a paper size detection device is disclosed. The paper size detection device is equipped with a guide member that can freely move for regulating an end portion of the paper contained in the paper cassette; a reflective member provided in the guide member, having a plurality of reflective surfaces in which the reflectance differs along the moving direction of the guide member; and a light receiving and emitting element for emitting light to the reflective surfaces of the reflective member, receiving the reflected light from the reflective surfaces, and outputting a detection signal corresponding to the amount of light received from the reflective surfaces. Furthermore, in patent document 2, a form of a transmitting member having a plurality of transmitting surfaces with different transmittances is also disclosed instead of a form of a reflective member having a plurality of reflective surfaces. 
     [Patent Document] 
     [Patent Document 1] Japanese Unexamined Application Publication No. 2011-254216 
     [Patent Document 2] Japanese Unexamined Application Publication No. 2001-322723 
     SUMMARY 
     In the document detection sensor of patent document 1, the sensor light emitted from the light emitter is reflected on the lower surface of the paper placed on the document feeding table via the detection holes, reaches the light receiving part, and is received by the light receiving part. However, for example, when the number of papers placed on the document feeding table is small, the sensor light emitted from the light emitter is transmitted through the paper, and the light receiving part may not be able to properly receive the sensor light. Alternatively, external light such as indoor illumination and the like may be transmitted through the paper, and the light receiving part may receive external light other than the sensor light. That is, in the document detection sensor of patent document 1, erroneous detection occurs easily, and in some cases, detection of paper size may not be reliably and appropriately carried out. 
     Furthermore, in the paper size detection device of patent document 2, a plurality of reflective surfaces having differing reflectance or a plurality of transmitting surfaces having differing transmittances corresponding to various types of paper sizes contained in the paper cassette are required. Thus, the detection device and the control mechanism thereof may become complicated, which increases the manufacture cost. 
     With the foregoing in mind, one or more embodiments of the invention may reliably and appropriately determine various sizes of a recording medium using a simple configuration. 
     The image forming apparatus according to one embodiment of the present invention is equipped with a housing; a mounting portion for mounting a recording medium, provided in the housing; at least one light receiving part provided in the housing; a change portion for changing the amount of light incident on the light receiving part based on the recording medium on the mounting portion, provided between the light receiving part and a light source for outputting light incident on the light receiving part; and a size determining part for determining size of the recording medium mounted in the housing, based on the amount of light received by the light receiving part that is changed by the change portion. 
     According to one or more embodiments of the present invention, because it is possible to change the amount of light incident on the light receiving part based on the recording medium on the mounting portion using the changing portion, it is possible to reliably and appropriately determine various sizes of a recording medium using a simple configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall perspective view illustrating the internal structure of a printer as viewed from above according to one or more embodiments of the present invention. 
         FIG. 2  is a partially enlarged perspective view illustrating the structure of the mounting portion according to one or more embodiments of the present invention, as viewed from above. 
         FIG. 3  is a perspective view illustrating the configuration of a substrate and a light emitter according to one or more embodiments of the present invention. 
         FIG. 4  is a cross-sectional view of the IV-IV line shown in  FIG. 1 . 
         FIG. 5  is a schematic view illustrating the positional relationship between the range wherein light can be received by the light receiving part (circular region T) and the through hole according to one or more embodiments of the present invention. 
         FIG. 6  is a block diagram illustrating a configuration of a printer according to one or more embodiments of the present invention. 
         FIG. 7  is a view corresponding to  FIG. 4  illustrating a variation of the printer according to one or more embodiments of the present invention. 
         FIG. 8  is an overall perspective view illustrating the internal structure of a printer as viewed from above according to one or more embodiments of the present invention. 
         FIG. 9  is a perspective view illustrating a configuration of the substrate, the light emitter, and the light receiver according to one or more embodiments of the present invention. 
         FIG. 10  is a partially enlarged perspective view illustrating the movement of the medium guide according to one or more embodiments of the present invention, as viewed from above. 
         FIG. 11  is a cross-sectional view of the XI-XI line shown in  FIG. 8 . 
         FIG. 12  is a view corresponding to  FIG. 11  illustrating a state in which the medium guide overlaps the through hole according to one or more embodiments of the present invention. 
         FIG. 13  is a circuit diagram illustrating the connected state of the light emitter and the light receiver according to one or more embodiments of the present invention. 
         FIG. 14  is a block diagram illustrating a configuration of a printer according to one or more embodiments of the present invention. 
         FIG. 15  is a view corresponding to  FIG. 11  illustrating a variation of the printer according to one or more embodiments of the present invention. 
         FIG. 16  is an overall perspective view of the internal structure of a printer as viewed from above according to one or more embodiments of the present invention. 
         FIG. 17  is a partially enlarged perspective view illustrating the structure of the mounting portion according to one or more embodiments of the present invention, as viewed from above. 
         FIG. 18  is a schematic diagram illustrating the relationship between the light emitter and the light receiver, and the light refractor according to one or more embodiments of the present invention. 
         FIG. 19  is a block diagram illustrating a configuration of a printer according to one or more embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described in detail below based on drawings. The following description of each embodiment is only an example, and is not intended to limit the present invention, its application, or its use. In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention. 
     Example 1 
       FIG. 1  illustrates a printer  1  according to one or more embodiments of the present invention. The printer  1  is an embodiment of the imaging formation device, and is applied, for example, as an inkjet printer. Note that in the printer  1  according to each embodiment described below, the position of a mounting portion  4  described later is set to the rear side of a housing  3  and the position of an ejection portion  5  is set to the front side (front surface side) of the housing  3 . Then, the horizontal direction orthogonal to the front and rear direction is the left and right direction, and the vertical direction orthogonal to the front and rear direction as well as the left and right direction is the up and down direction. 
     The printer  1  is equipped with a device body  2 . The device body  2  has a resin housing  3 , and a mounting portion  4  for mounting a paper as the recording medium is provided on the rear side of the housing  3  corresponding to various sizes. For example, the mounting portion  4  has a mounting surface  4   a  for mounting the paper of various sizes diagonally above. As illustrated in  FIG. 1 , the mounting surface  4   a  is formed in a range from a left side portion  4   b  to a right side portion  4   c  of the mounting portion  4 . Furthermore, as illustrated in  FIG. 4 , the mounting surface  4   a  is inclined only at a predetermined angle (30° in the illustrated example) from the vertical direction so that the upper side faces the rear side of the housing  3 . Then, the right side portion  4   c  of the mounting portion  4  is set as a reference position E (see  FIG. 1 ), and each paper is mounted on the mounting surface  4   a  in a state where the side portions of each paper are aligned with the reference position E. 
     The ejection portion  5  is provided on the front side in the housing  3  to eject the paper fed from the mounting portion  4  into the housing  3 . The paper mounted on the mounting surface  4   a  of the mounting portion  4  is sent to the ejection portion  5  along a transporting direction orthogonal to the width direction of the housing  3  using a feeding mechanism (not illustrated) provided in the housing  3 . 
     Furthermore, the device body  2  is equipped with a cartridge  6  having a nozzle (not illustrated) for discharging ink, and a carriage  7  on which the cartridge  6  is mounted. The carriage  7  is configured to be able to reciprocate in the left and right direction in the housing  3 . An image or the like is printed on a paper fed from the mounting portion  4  into the housing  3  by discharging ink from the nozzle of the cartridge  6  while reciprocating the carriage  7  in the left and right direction within the housing  3 . 
     Next, as illustrated in  FIG. 1 ,  FIG. 2 , and  FIG. 4 , a plurality (three in the illustrated example) of through holes  8  ( 8   a,    8   b,    8   c ) for passing through the mounting portion  4  are provided in the mounting portion  4 . As illustrated in  FIG. 5 , the opening of each through hole  8  is formed in substantially a triangular shape so as to taper in the transporting direction. For example, the opening of each through hole  8  is formed in a right angle isosceles triangle in which the lower vertex angle is a right angle. Furthermore, as illustrated in  FIG. 4 , each through hole  8  is formed to pass through from the mounting surface  4   a  to each light receiving part  12  described later. 
     The through holes  8   a,    8   b,  and  8   c  are disposed at intervals along the width direction of the housing  3  so as to correspond to each paper size mounted in the mounting portion  4 . For example, as illustrated in  FIG. 1 , the through hole  8   a  formed near the left side portion  4   b  of the mounting portion  4  is disposed so that the center of the left and right width thereof is positioned at a position separated from the reference position E only by the dimension X 1 . Furthermore, the through hole  8   b  formed second from the left side is disposed so that the center of the left and right width thereof is positioned at a position separated from the reference position E only by a dimension X 2 . The through hole  8   c  formed near the right side portion  4   c  of the mounting portion  4  is provided to detect the presence and absence of a paper mounted in the mounting portion  4 . 
     Here, the dimension X 1  corresponds to a length (297 mm) in the longitudinal direction in an A4 sized paper horizontally placed on the mounting surface  4   a  of the mounting portion  4 , or a length (279.4 mm) in the longitudinal direction in a letter size paper. Furthermore, the dimension X 2  corresponds to a length (257 mm) in the longitudinal direction in a B5 size paper horizontally placed on the mounting surface  4   a  of the mounting portion  4 . 
     Furthermore, as illustrated in  FIG. 1 ,  FIG. 2 , and  FIG. 4 , a plurality (three in the illustrated example) of a light receiving part  12  ( 12   a,    12   b,  and  12   c ) is disposed in a position corresponding to the position of each through hole  8 . Each light receiving part  12  is stored in a storage space  13   a  in a storage space  13  described later. Furthermore, each light receiving part  12  is composed of, for example, a phototransistor for visible light. The light incident on the phototransistor is converted into a voltage in the phototransistor. The voltage is input in an AD converter (not illustrated) via an integrated circuit (not illustrated) in the device body  2 , and is converted to a digital value using the AD converter. Then, the digital value is output to a size determining part  14  described later. 
     Here, as illustrated in  FIG. 4 , in the printer  1  according to the present embodiment, an illumination light or the like installed on the outside of the housing  3  (for example, indoors) is used as the light source S, and the light output from the illumination light becomes the light L incident on each light receiving part  12 . 
     As illustrated in  FIG. 3 , each light receiving part  12  is provided on a rectangular substrate  10 . For example, the plurality of light receiving part  12   a,    12   b,  and  12   c  are placed at predetermined intervals along the longitudinal direction of the substrate  10  in a state rising in a direction orthogonal to the substrate  10  surface. 
     As illustrated in  FIG. 4 , the storage space  13  having a predetermined storage space  13   a  is provided on the opposite side of the mounting surface  4   a  of the mounting portion  4 . The storage space  13  and the storage space  13   a  is formed so as to extend in the width direction of the housing  3 . A support portion  13   b  protruding into the storage space  13   a  is integrally formed in the storage space  13 , and the substrate  10  is fixed to the support portion  13   b.    
     As a characteristic of the printer  1  according to the present embodiment, each through hole  8  is disposed at a position shifted more upward than the position of each light receiving part  12  in the transporting direction of the paper P along the mounting surface  4   a  of the mounting portion  4 . In other words, as illustrated in  FIG. 2  and  FIG. 4 , each light receiving part  12  is stored in the storage space  13   a  of the storage space  13  in a state hidden behind the mounting portion  4  as viewed from the front surface side of the housing  3 . Furthermore, as illustrated in  FIG. 5 , a circular region T indicated by a virtual line represents a standard region in which light can be received by the light receiving part  12 , and each through hole  8  is disposed corresponding to each light receiving part  12  so that the opening is partially included in the circular region T. 
     Due to the positional relationship between the through holes  8  and the light receiving parts  12 , in a state in which there is no paper P in the mounting portion  4 , the light L output from the light source S passes through the through hole  8  and is incident on each light receiving part  12  so as to be along an inclined direction inclined upward by only a predetermined angle with respect to the protruding direction of the light receiving part  12  (see  FIG. 4 ). 
     Furthermore, as described above, because the through hole  8  is disposed at a position shifted upward from the position of the light receiving part  12 , as indicated by the virtual line in  FIG. 4 , the light L passes through a region more narrow than the actual opening in the through hole  8  and incident in the light receiving part  12 . That is, the incident angle of the light L when incident on the light receiving part  12  is limited by the positional relationship of the through hole  8  and the light receiving part  12 , and the light L incident on the light receiving part  12  is narrowed. Thus, the light L slightly attenuates as it passes through the through hole  8 . Then, the amount of light L is slightly smaller than the amount of light immediately after being output from the light source S to being incident on the light receiving part  12  from the through hole  8 . However, because the opening of the through hole  8  as described above is partially included in the circular region T, even when the light receiving part  12  is hidden behind the mounting portion  4 , the light L passing through the through hole  8  is directly incident on the light receiving part  12 . 
     Meanwhile, as illustrated in  FIG. 4 , in a state in which there is a paper P on the mounting portion  4 , the light L passes through the paper P so as to be inclined with respect to the thickness direction, and the light L is significantly attenuated in the process. For example, due to the through hole  8  being disposed in a state shifted from the light receiving part  12 , the light L incident on the light receiving part  12  is narrowed down in the through hole  8 , and for example, compared to a state in which the position of the through hole  8  is aligned with the light receiving part  12 , and the light L passes through in the vertical direction with respect to the paper P on the mounting surface  4   a,  it can be secured for a longer distance (attenuation distance) until the light L is incident on the light receiving part  12 . Then, due to the paper P and the through hole  8  mounted on the mounting surface  4   a  the amount of light L incident on the light receiving part  12  significantly attenuates more than the light amount when output from the light source S. As a result, there is an amount of light L smaller than when no paper P is on the mounting portion  4  is incident on light receiving part  12  in a position in which the though hole  8  is blocked by the paper P. 
     Then, as illustrated in  FIG. 6 , the printer  1  has a size determining part  14  for determining the size of each paper mounted on the mounting portion  4  based on the amount of light incident on the light receiving part  12 , and the number and position of light receiving part  12  on which the light L is incident. For example, the aspect for determining various sizes of paper are as follows. 
     In the size determining part  14 , when an output voltage (hereinafter “output voltage V 1 ”) is detected corresponding to when the amount of light L attenuated from all of the light receiving part  12   a,    12   b , and  12   c  is incident, the size determining part  14  determines that an A4 size paper or a letter size paper is mounted on the mounting portion  4  in a horizontal state. 
     In the size determining part  14 , when an output voltage (hereinafter “output voltage V 2 ”) is detected corresponding to when the amount of light L not attenuated from only light receiving part  12   a  is incident (that is, the light L guided from the through hole  8   a  to the direct light receiving part  12   a  without passing through the paper P), and when the output voltage V 1  from the other light receiving part  12   b  and  12   c  are detected, the size determining part  14  determines that a B5 size paper is mounted on the mounting portion  4  in a horizontal state. 
     In the size determining part  14 , when the output voltage V 2  from both light receiving part  12   a  and  12   b  is detected, and when the output voltage V 1  from the light receiving part  12   c  is detected, the size determining part  14 , for example, determines that a postcard size paper, paper less than or equal to B5 size, envelope, L size, and the like is mounted in the mounting portion  4 . 
     In the size determining part  14 , when the output voltage V 2  is detected from all of the light receiving part  12   a,    12   b,  and  12   c,  the size determining part  14  determines that no paper of any size is mounted on the mounting portion  4 . 
     Then, as illustrated in  FIG. 6 , the size determining part  14  sends each determination result to a controller  15  composed of a CPU provided in the device body  2 . The controller  15  operates each mechanism such as the carriage  7  and the like based on the determination results. In one or more embodiments of the invention, the paper size determining part  14  may be implemented in software that is performed by the controller  15  or the CPU thereof. 
     (Operation Effect of Example 1) 
     As described above, the through hole  8  is configured so that the path of the light L incident on the light receiving part  12  is narrowed in advance. Then, as described above, in a state in which there is paper P on the mounting portion  4 , the amount of light L output from the light source S is significantly attenuated by the paper P and the though hole  8 , and the amount of light L smaller than the state in which no paper P is on the mounting portion  4  is incident on the light receiving part  12 . As a result, it is possible to reliably distinguish the amount of light L incident on the light receiving part  12  based on the paper P mounted on the mounting portion  4 . That is, the through hole  8  is provided between the light receiving part  12  and the light source S, and functions as a change portion (light guiding portion) for changing the amount of light L when the light L from the light source S is incident on the light receiving part  12  based on the presence and absence of paper P on the mounting portion  4 . 
     Therefore, in the printer  1  according to this embodiment, it is possible to change the amount of light when the light L from the light source S is incident on the light receiving part  12  based on the paper P on the mounting portion  4 , and reliably and appropriately determine the paper size so that erroneous detection does not occur. 
     Furthermore, in the printer  1  according to this embodiment, by providing a through hole  8  passing through from the mounting surface  4   a  to the mounting portion  4  to the light receiving part  12 , the mechanism for detecting the paper size equipped with a change portion (light guiding portion) can be simplified, and the cost of the device body in the printer  1  can be reduced. 
     Furthermore, because the storage space  13  having a storage space  13   a  for storing the light receiving part  12  is provided on the opposite side of the mounting surface  4   a  in the mounting portion  4 , the light L guided from the through hole  8  can be effectively caused to be incident on the light receiving part  12 . 
     Furthermore, because the opening in each through hole  8  is formed in substantially a triangular shape so as to taper toward the transporting direction, when setting the paper P on the mounting portion  4  (mounting surface  4   a ) along the transporting direction, the lower end portion of the paper P does not catch on each through hole  8 , and the paper P can be smoothly mounted on the mounting portion  4  (mounting surface  4   a ). 
     Furthermore, in the printer  1  according to this embodiment, because an illumination light and the like on the outside of the housing  3  is used as the light source S, it is unnecessary to additionally provide a dedicated light emitter composed of an LED as the light source S, and the mechanism for detecting the paper size can be simplified, thus reducing the cost of the device body in the printer  1 . 
     (Variation of Example 1) 
       FIG. 7  illustrates a variation of example 1.Note that in the following variation and the description of the embodiments, the same portions in  FIG. 1 through 6  will be denoted by the same reference numerals, and a detailed description thereof will be omitted. 
     As illustrated in  FIG. 7 , each through hole  8  is formed at an incline with respect to the mounting surface  4   a  so as to pass through from the mounting surface  4   a  on the mounting portion  4  to each light receiving part  12 . By providing the through hole  8  as such, the light L passing through along the hole direction of the through hole  8  can be caused to be more efficiently incident on each light receiving part  12 . 
     In particular, the through hole  8  in the variation is configured to incline only at a predetermined angle θ (θ=30° in the illustrated example) with respect to the mounting surface  4   a.  Thus, for example, compared to the through hole  8  in which the angle θ is formed to be 90° (that is, a state formed to pass through in the vertical direction with respect to the mounting surface  4   a ), the distance from the paper P to each light receiving part  12  is approximately doubled, and the attenuation distance of the light L can be secured to a longer distance. As a result, the amount of light L incident on the light receiving part  12  can more reliably be distinguished based on the presence and absence of paper P mounted on the mounting portion  4 . Note that the angle θ in this variation is set to 30°, but it is not limited to this angle, and may be set to an angle less than 90°. 
     (Another example relating to example 1) 
     In the printer  1  according to this embodiment, an aspect using the through hole  8  as the change portion (light guiding portion) is illustrated, but it is not limited to this. For example, it may be a light guiding portion in which each through hole  8  is blocked by a transparent member such as a transparent glass member, acrylic member, and the like. In this case, the opening of each through hole  8  is not limited to the substantially triangular shape as described above, and may be formed in a polygonal shape including a square shape, or a circular shape. That is, the change portion (light guiding portion) is provided between the light receiving part  12  and the light source S, and may function for changing the amount of light when the light L from the light source S is incident on the light receiving part  12  based on the presence and absence of paper P on the mounting portion  4 . 
     Example 2 
       FIG. 8 through 14  illustrate the printer  1  according to one or more embodiments of the present invention. In this embodiment, compared to example 1, the specific configuration differs in the light source, the through hole, and the change portion. Note that in the following description, the same portions in  FIG. 1 through 7  will be denoted by the same reference numerals, and a detailed description thereof will be omitted. 
     In this embodiment, as illustrated in  FIG. 8  and  FIG. 12 , a plurality (three in the illustrated example) of through holes  20  ( 20   a,    20   b,    20   c ) formed passing through in a substantially rectangular shape are provided in the mounting portion  4 . The through holes  20   a,    20   b,  and  20   c,  similar to example  1 , are disposed at intervals along the width direction of the housing  3  in positions to correspond to each paper P size mounted in the mounting portion  4 . 
     As illustrated in  FIG. 8 through 12 , in the printer  1  according to this embodiment, a plurality (three in the illustrated example) of light receiving part  12  ( 12   a,    12   b,    12   c ) composed of a phototransistor are provided in the housing  3 . Furthermore, a plurality (three in the illustrated example) of light emitters  11  ( 11   a ,  11   b ,  11   c ) composed of an LED element are provided as the light source in the housing  3 , and the light output from the end portion of each light emitter  11  is the light L incident on the end portion of each light receiving part  12 . 
     For example, each light emitter  11  and each light receiving part  12  are disposed close to each other so as to form a pair on positions corresponding to the position of each through hole  20  on the opposite side (back side) of the mounting surface  4   a  on the mounting portion  4 . As illustrated in  FIG. 9 , each light emitter  11  and each light receiving part  12  are placed at a predetermined interval on the substrate  10  along the longitudinal direction of the substrate  10  in a state raising in a vertical direction with respect to the back side of the substrate  10  and, for example, forming a pair vertically. Note that in this embodiment, the light emitters  11   a,    11   b,  and  11   c  are disposed on the upper side, and furthermore, the light receiving part  12   a,    12   b,  and  12   c  are respectively disposed on the lower side. As also illustrated in  FIG. 11  and  FIG. 12 , each light emitter  11  and each light receiving part  12  are stored in the storage space  13   a  in a state in which the substrate  10  is fixed to the supporting portion  13   b  of the storage space  13 . 
     As illustrated in  FIG. 13 , each light receiving part  12  is in a state of always being able to receive the light L output from the each light emitter  11 , and when the light L is reflected, the reflected light L is incident on each adjacent light receiving part  12 . As illustrated in  FIG. 14 , each light receiving part  12 , similar to example  1 , is configured so as to output a voltage corresponding to the amount of incident light L to the size determining part  14 . 
     As a characteristic of the printer  1  according to this embodiment, as illustrated in  FIG. 8 , the printer  1  is equipped with a medium guide  21  that can move along the width direction of the mounting portion  4 . As illustrated in  FIG. 10 , the medium guide  21  stops at a position overlapping any one of the through holes  20   a,    20   b,  and  20   c,  and is configured to limit the position of each paper P by holding the end portion of each paper P mounted on the mounting surface  4   a  on the mounting portion  4  in the stopped position. 
     Furthermore, as illustrated in  FIG. 12 , the reflective surface  22  is formed in the medium guide  21  on the side opposite the mounting surface  4   a  on the mounting portion  4 . The reflective surface  22  is treated, for example, as a mirror surface so as to increase the reflectance of light. That is, the reflective surface  22  is configured so as to reflect the light L toward the light receiving part  12  at a portion within the through hole  20  when the through hole  20  is blocked by overlapping any one of the through holes  20   a,    20   b,  and  20   c  by the movement of the medium guide  21 . 
     The size determining part  14  according to this embodiment is configured so as to determine the size of each paper P mounted on the mounting portion  4  based on the amount of light L to the light receiving part  12  reflected by the reflective surface  22  on the medium guide  21 . Furthermore, each light receiving part  12  is set so that the medium guide  21  does not overlap the through hole  20 , the output voltage is not the maximum value when the light L reflected by the paper P is incident, and the output voltage is the maximum value when the light L reflected by the reflective surface  22  of the medium guide  21  is incident due to the medium guide  21  overlapping the through hole  20 . The aspect for determining the specific size of each paper will be described below. 
     The size determining part  14  determines that an A4 size or letter size paper P is mounted on the mounting portion  4  when the size determining part  14  detects an output voltage of the maximum value from only the light receiving part  12   a  and an output voltage less than the maximum value from the other light receiving part  12   b  and  12   c.  In this case, as illustrated in  FIG. 10 , the medium guide  21  overlaps the through hole  20   a.    
     The size determining part  14  determines that a B5 size paper P is mounted on the mounting portion  4  when the size determining part  14  detects an output voltage of the maximum value from only the light receiving part  12   b  and detects an output voltage less than the maximum value from only the light receiving part  12   c.  In this case, as illustrated in  FIG. 10 , the medium guide  21  overlaps the through hole  20   b.    
     The size determining part  14  determines that a postcard size paper P is mounted on the mounting portion  4  when the size determining part  14  detects an output voltage less than the maximum value from only the light receiving part  12   c,  and does not detect an output voltage from the other light receiving part  12   a  and  12   b.  In this case, as illustrated in  FIG. 10 , the medium guide  21  is positioned between the through hole  20   b  and the through hole  20   c.    
     Note that the size determining part  14  determines that no paper P of any size is mounted on the mounting portion  4  when an output voltage is not detected from the light receiving part  12   c.    
     Then, as illustrated in  FIG. 14 , the size determining part  14  sends each determination result to the controller  15 . The controller  15  operates each mechanism such as the carriage  7  and the like based on the determination results. 
     The other configurations of the printer  1  in example 2 are similar to the configurations of the printer  1  according to example 1. 
     (Operation Effect of Example 2) 
     As described above, the medium guide  21  (reflective surface  22 ) in this embodiment is interposed between the light receiving part  12  and the light emitter  11 , and functions as the change portion for changing the amount of light L based on the paper P on the mounting portion  4  when the light L from the light emitter  11  is incident on the light receiving potion  12 . Then, in the printer  1  according to this embodiment, the position of each paper P mounted on the mounting surface  4   a  on the mounting portion  4  can easily be aligned using the medium guide  21 , and the amount of light can be changed when the light L from each light emitter  11  is incident on the light receiving part  12  based on the paper P on the mounting portion  4  by using the medium guide  21  (reflective surface  22 ) correlating to the change portion. Therefore, in the printer  1  according to this embodiment, the paper size can also be reliably and appropriately determined. 
     Furthermore, the light receiving part  12  is set so that the output voltage is the maximum voltage when the light L reflected by the reflective surface  22  on the medium guide  21  is incident by the medium guide  21  overlapping the through hole  20 . Therefore, the difference between the output voltage having the maximum value and the output voltage from the light receiving part  12  when the light L reflected on the rear surface of the paper P in the through hole  20  is incident by the medium guide  21  not overlapping the through hole  20  appears large. Due to this voltage difference, both output voltages can be reliably distinguished, and erroneous detection of the paper size by the size determining part  14  can be prevented in advance. 
     (Variation of Example 2) 
       FIG. 15  illustrates a variation of the example 2. Note that in the following description, the same portions in  FIG. 7 through 14  will be denoted by the same reference numerals, and a detailed description thereof will be omitted. 
     In this variation, as illustrated in  FIG. 15 , for each light emitter  11  and each light receiving part  12 , each light receiving part  12  is disposed on the upper side while each light emitter  11  is disposed on the lower side. Furthermore, a plurality of slits  23  are provided in the mounting portion  4 . For example, the slits  23  are formed to pass through a horizontally elongated hole at the position of each through hole  20  opposing each light receiving part  12  and disposed at intervals in the vertical direction. The other configurations of the printer  1  according to this variation are similar to the configuration of the printer  1  according to example 2. 
     By providing such slits  23 , it is possible to shield the light from outside the housing  3  (for example, light output from an interior illumination light) in front of each light receiving part  12  so to not be incident on each light receiving part  12 . As a result, when there is no paper on the mounting surface  4   a  on the mounting portion  4 , light from the outside of the housing  3  being incident on the light receiving part  12  is prevented, and it is possible to reliably determine that there is no paper on the mounting surface  4   a  of the mounting portion  4  by the size determining part  14 . 
     Example 3 
       FIG. 16 through 19  illustrate the printer  1  according to one or more embodiments of the present invention. In this embodiment, the specific configuration of the light emitter, light receiving part, and change portion differs compared to example 2. Furthermore, in the printer  1  according to one or more embodiments of the present invention, through holes  20  as in example 2 are not provided. Note that in the following description, the same portions in  FIG. 8 through 14  will be denoted by the same reference numerals, and a detailed description thereof will be omitted. 
     In the printer  1  according to this embodiment, one light emitter  11  composed of an LED element provided in the housing  3  is used as the light source. As illustrated in  FIG. 16 through 18 , the light emitter  11  is provided at one end portion in the width direction of the mounting portion  4 . For example, a substantially plate-shaped first attachment plate  31  extending in the front and back direction is fixed to, for example, a left side portion  4   b  on the mounting portion  4 , and the light emitter  11  is attached to, for example, a right side surface of the first attachment plate  31  so as to output the light L (see  FIG. 18 ) towards the right direction (inner side in the width direction of the housing  3 ). 
     Furthermore, the light receiving part  12  is provided in the light emitter  11  opposing the left and right direction on the other end portion in the width direction of the mounting portion  4 . For example, a substantially plate-shaped second attachment plate  32  extending in the front and back direction is fixed to a right side portion  4   c  on the mounting portion  4 , and the light receiving part  12  is attached to, for example, a left side surface of the second attachment plate  32  so as to face the left and right direction, that is, towards the light emitter  11  side. The light receiving part  12  is composed of a phototransistor, similar to example 2. Then, the light emitter  11  and the light receiving part  12  are disposed so as to be positioned on the same straight line M in a position at the same height, and the light L output from the light emitter  11  is incident on the light receiving part  12 . 
     As illustrated in  FIG. 16  to  FIG. 18 , the printer  1  is equipped with a medium guide  21  that can move along the width direction of the mounting portion  4  (direction of straight line M). The medium guide  21 , similar to example 2,is configured so as regulate the position of each paper P with respect to the mounting portion  4  by holding the inner portion of each paper P mounted on the mounting surface  4   a  on the mounting portion  4 . Note that the medium guide  21  in this example, differing from example 2, does not have a reflective surface  22  formed. 
     Furthermore, as a characteristic of the printer  1  according to this embodiment, a substantially plate-shaped light refractor  33  positioned on the straight line M connecting the light emitter  11  and the light receiving part  12  is fixed in the front end portion of the medium guide  21 . The light refractor  33  refracts the light L output from the light emitter  11  and incident on the light receiving part  12  in the middle, and is formed in a substantially rectangular shape as viewed from the side surface, composed of, for example, a transparent glass material or acrylic material. 
     In addition, as illustrated in  FIG. 18 , the light refractor  33  has an incident surface  34  whereon the light L from the light emitter  11  is incident and is orthogonal to the incident direction of the light L (that is, the direction of straight line M), and an emission surface  35  inclined at only a predetermined angle (10° in the illustrated example) with respect to the incident surface  34  and for emitting light L incident on the incident surface  34  to the light receiving part  12 . For example, the emission surface  35  is inclined so as to come closer to the incident surface  34  side (left side of the housing  3 ) facing the front side of the housing  3 . Due to such an inclined emission surface  35 , the light refractor  33  is configured so as to cause the light L output from the light emitter  11  towards the light receiving part  12  to be incident on the light receiving part  12  by refracting toward the front side of the housing  3  only at a predetermined angle with respect to the straight line M direction. 
     In the printer  1  according to this embodiment, the refractive position of the light L from the light refractor  33  on the straight line M is changed according to the position of the medium guide  21 , and changes the amount of light L incident on the light receiving part  12 . Then, the size determining part  14  (see  FIG. 19 ) is configured to determine the size of each paper P mounted on the mounting portion  4  based on the change in amount of light L incident on the light receiving part  12  corresponding to the position of the medium guide  21 . The aspect for determining the specific size of each paper P is as follows. 
     As illustrated in  FIG. 18 , when the position of the medium guide  21  is aligned with the maximum size paper P mounted on the mounting portion  4 , the medium guide  21  is in a state separated from the light receiving part  12  as much as possible (the light reactive portion  33  is positioned at point A). In this state, the distance in the front and back direction between the light L refracted by the light refractor  33  and the light receiving part  12  is a maximum. Then, the amount of light L incident on the light receiving part  12  is a minimum, and the value of the voltage output from the light receiving part  12  is a minimum. Thus, when the size determining part  14  detects a minimum output voltage, the size determining part  14  determines that the maximum size (for example, letter size) paper P is mounted on the mounting portion  4 . 
     Meanwhile, when the position of the medium guide  21  is aligned with the minimum size paper P mounted on the mounting portion  4 , the medium guide  21  is in a state as close to the light receiving part  12  as possible (the light reactive portion  33  is positioned at point D). In this state, the distance in the front and back direction between the light L refracted by the light refractor  33  and the light receiving part  12  is a minimum. Then, the amount of light L incident on the light receiving part  12  is a maximum, and the value of the voltage output from the light receiving part  12  is maximum. Thus, when the size determining part  14  detects a minimum output voltage, the size determining part  14  determines that the minimum size (for example, postcard size) paper P is mounted on the mounting portion  4 . 
     Furthermore, when the position of the medium guide  21  is aligned with vertically placed A4 sized paper P mounted on the mounting portion  4 , and when the light refractor  33  is positioned at point B separated at only a predetermined distance from reference position E, the voltage value output from the light receiving part  12  becomes a predetermined voltage value due to the change in distance in front and back direction between the light L refracted by the light refractor  33  and the light receiving part  12 . In addition, when the position of the medium guide  21  is aligned with the vertically placed B5 sized paper P mounted on the mounting portion  4 , and when the light refractor  33  is positioned at point C separated only a predetermined distance from the reference point E, a voltage larger than in the case of the A4 size is output from the light receiving part  12 . Thus, the size determining part  14  determines the size of each paper P mounted on the mounting portion  4  by the voltage value output from the light receiving part  12 . 
     Note that in  FIG. 17 , a state is illustrated in which the position of the medium guide  21  is aligned with a vertically placed A4 sized paper P mounted on the mounting portion  4 . 
     Then, as illustrated in  FIG. 19 , the size determining part  14  sends each determination result to the controller  15 . The controller  15  operates each mechanism such as the carriage  7  and the like based on the determination results. 
     (Operation Effect of Example 3) 
     As described above, the light refractor  33  is provided between the light emitter  11  and the light receiving part  12 , and functions as a change portion that changes the amount of light based on the paper P on the mounting portion  4  when the light L from the light emitter  11  is incident on the light receiving part  12 . Then, in the printer  1  according to this embodiment, it is possible to easily align the position of each paper P mounted on the mounting surface  4   a  on the mounting portion  4  using the medium guide  21 . Along with that, due to the light refractor  33  (change portion) moving along with the medium guide  21 , because the amount of light L incident on the light receiving part  12  changes based on the paper P on the mounting portion  4 , the paper size can be reliably and easily determined. Furthermore, in the printer  1  according to this embodiment, because it may be configured to provide the one of the light emitters  11  and the light receiving part  12 , the mechanism for detecting the paper size can be simplified, and cost of the entire device body in the printer  1  can be reduced. 
     Furthermore, in the light refractor  33 , the light L output from the light emitter  11  is incident on the incident surface  34  and passes through the inside of the light refractor  33  along the direction of the straight line M. Meanwhile, the light L passing through the inside of the light refractor  33  is refracted toward the front side of the housing  3  by the emission surface  35  at only a predetermined angle with respect to the direction of the straight line M. In addition, the light refractor  33  is integrally provided with the medium guide  21 , and is configured so as to move along the straight line M along with the medium guide  21 . Therefore, due to the medium guide  21  being caused to move, while maintaining an angle of the incident surface  34  and the emission surface  35  with respect to the straight line M, it is possible for the light refractor  33  (incident surface  34  and emission surface  35 ) to move closer to or separate farther from the light receiving part  12 . Meanwhile, when the light L is refracted by the emission surface  35  at a position where the light refracting portion  33  is separated far from the light receiving part  12  (for example, position of point A illustrated in  FIG. 18 ), the amount of light L incident on the light receiving part  12  decreases. Meanwhile, when the light L is refracted by the emission surface  35  at a position where the light refracting portion  33  is close to the light receiving part  12  (for example, position of point D illustrated in  FIG. 18 ), the amount of light L incident on the light receiving part  12  increases. Thus, the amount of light L incident on the light receiving part  12  corresponding to the position of the light refractor  33  can be changed. 
     Furthermore, the light receiving part  12  is composed of a phototransistor, and outputs a predetermined voltage value corresponding to the amount of input light. Then, when the position of the medium guide  21  is aligned with the minimum sized paper P mounted on the mounting portion  4 , the medium guide  21  is as close as possible to the light receiving part  12 . Therefore, when the position of the medium guide  21  is aligned with the minimum size paper P, the amount of light L incident on the light receiving part  12  by being refracted by the light refractor  33  is a maximum. That is, the voltage output from the light receiving part  12  is a maximum. By such a configuration, when the position of the medium guide  21  is aligned with the minimum size paper P mounted on the mounting portion  4 , the size determining part  14  can determine the size of each paper P mounted on the mounting portion  4  using the voltage output from the light receiving part  12  as a reference. 
     (Another Example Relating to Example 3) 
     In this embodiment, an aspect is illustrated where one light emitter  11  composed of an LED element is used as the light source, but it is not limited to this. That is, as described in the first example described above, an illumination light and the like mounted on the outside of the housing  3  may be used as the light source. 
     Another Embodiment 
     In each of the embodiments described above, an example is given of the printer  1 , which is one embodiment for the image forming apparatus, but it is not limited to this. For example, one or more embodiments of the present invention may be applied to an image forming apparatus such as a compound device integrally combined with a scanner or printer function, and the like. 
     Embodiments for the present invention are described above, but the present invention is not limited to the above embodiments, and can have various variations within the scope of the invention. 
     Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims. 
     One or more embodiments of the present invention is industrially applicable, for example, as an inkjet printer. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1 : Printer 
           2 : Device Body 
           3 : Housing 
           4 : Mounting Portion 
           4   a : Mounting Surface 
           8 ,  20 : Through Hole 
           11 : Light emitter 
           12 : Light Receiving Part 
           13 : Storage space 
           13   a : Storage Space 
           14 : Size Determining Part 
           15 : Controller 
           21 : Medium guide 
           22 : Reflective Surface 
           23 : Slit 
           33 : Light refractor 
           34 : Incident Surface 
           35 : Emission Surface 
         L: Light