Patent Publication Number: US-11650533-B2

Title: Image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/136,081, filed Sep. 19, 2018, which claims the benefit of Japanese Patent Application No. 2017-187433 filed Sep. 28, 2017 and No. 2018-139976 filed Jul. 26, 2018, all of which are hereby incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to an image forming apparatus that forms an image on a recording medium. 
     Description of the Related Art 
     There is a conventional image forming apparatus in which, when detecting portions that detect a recording medium are provided in a plurality of units, a control board and detection boards are provided as separate boards, and the control board and the detection boards are connected to each other with bundle wire so that the detection boards are disposed directly in the units. By providing the detection boards in the units, errors regarding the detection accuracy can be reduced. 
     Furthermore, there is an image forming apparatus in which a plurality of detecting portions are provided on a single board disposed in a direction orthogonal to a conveyance path of the recording medium, and in which the plurality of detecting portions detect to the plurality of unit whether there is a recording medium present (Japanese Patent Laid-Open No. 2002-123048). 
     Furthermore, there is an apparatus that directly detects whether there is a recording medium present by providing a plurality of detecting portions on a board that has been set close to parallel to a conveyance path of the recording medium (Japanese Patent Laid-Open No. 2009-122518). 
     However, when a plurality of detecting portions are provided in a single board to achieve cost reduction, and when detection of a presence of a recording medium is performed for a plurality of units, the detection error becomes large when there is a shift between the positions of the units. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides an image forming apparatus in which a sheet can be detected accurately with a plurality of detecting portions on the same board, which correspond to a plurality of units. 
     Further features and aspects of the present disclosure will become apparent from the following description of example embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic cross-sectional view illustrating a schematic configuration of an example image forming apparatus. 
         FIG.  2    is a perspective view illustrating the schematic configuration of the image forming apparatus. 
         FIG.  3    is a diagram illustrating an example conveyance path of the image forming apparatus. 
         FIGS.  4 A and  4 B  are cross-sectional views illustrating an example operation of a registration detection flag. 
         FIGS.  5 A and  5 B  are cross-sectional views for describing example operations of a discharge detection flag and a sheet width detection flag. 
         FIG.  6    is a diagram of an inside of the image forming apparatus viewed from a front side. 
         FIG.  7    is a perspective view of an inside of the image forming apparatus viewed from a rear side. 
         FIG.  8    is a diagram of an example electric board viewed from a front side of the image forming apparatus. 
         FIG.  9    is a cross-sectional view around the electric board viewed from the front side of the image forming apparatus. 
         FIG.  10    is a diagram of an inside of the image forming apparatus viewed from the rear side. 
         FIGS.  11 A to  11 C  are diagrams illustrating a connection between a transfer portion conveying unit and a fixing portion discharge unit. 
         FIG.  12    is a diagram of the electric board viewed from the front side of the image forming apparatus. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, referring to the drawings, a preferred embodiment of the disclosure will be exemplified in detail. Note that the dimensions, the materials, and the shapes of the components and the relative configuration of the components, and the like that are described in the following embodiment is to be appropriately changed based on the device, to which the present disclosure is applied, and various conditions. Accordingly, unless otherwise specified in particular, the scope of the present disclosure is not intended to be limited by the embodiment described below. 
     Referring first to  FIGS.  1  to  3   , an example image forming apparatus of the present embodiment will be described.  FIG.  1    is a cross-sectional view illustrating a schematic configuration of a monochrome laser beam printer that is an example of the image forming apparatus according to the present embodiment, and  FIG.  2    is a perspective view of the monochrome laser beam printer.  FIG.  3    is a cross-sectional view of the monochrome laser beam printer and is a diagram illustrating a conveyance path of sheets such as recording paper. 
     An image forming operation of an image forming apparatus  1  will be described briefly. As illustrated in  FIGS.  1  to  3   , sheets  20  serving as recording mediums stacked on a tray are fed sheet by sheet from the top with a feed roller  2  serving as a feeding portion. Subsequently, the sheet  20  is conveyed further downstream with respect to a conveyance roller  3  serving as a conveying portion and is sent to a transfer portion  4 . The transfer portion  4  transfers an image formed on a drum  90  serving as an image bearing member that constitutes an image forming portion onto the conveyed sheet  20 . The sheet  20  is sent further downstream and while being conveyed through a fixing portion  5 , the image is fixed to the sheet  20  with heat. The sheet  20  is discharged external to the device with discharge rollers  6  serving as a discharge portion. 
     Referring next to  FIGS.  4 A to  6   , detection of the conveyed sheet  20  will be described.  FIGS.  4 A and  4 B  are cross-sectional views for describing an operation of a registration detection flag  30 .  FIGS.  5 A and  5 B  are cross-sectional views for describing operations of a discharge detection flag  60  and a sheet width detection flag  63 .  FIG.  6    is a diagram illustrating the inside of the printer viewed from the front side. 
     As illustrated in  FIGS.  4 A and  4     b , the registration detection flag  30  serving as a second pivotably moving member moving pivotably in a conveyance direction is provided between the feed roller  2  and the conveyance roller  3 . The registration detection flag  30  is pivoted in the sheet conveyance direction about a rotating shaft  33  by having a front edge  21  of the sheet  20  in the conveyance direction come in contact with a contact portion  31  of the registration detection flag  30  and by being pushed by the sheet  20 . The registration detection flag  30  includes a light shielding portion  32  on a side opposite the contact portion  31  with the rotating shaft  33  in between. The light shielding portion  32  of the registration detection flag  30  is switched so that a light of a photointerrupter  70  serving as a second detecting portion disposed on an electric board  7  described later is transmitted or shielded. With the above, the state of the sheet can be detected from a rotation state (a pivot state) of the registration detection flag  30 . Note that when in a state in which there is no sheet in the conveyance path, the light is shielded (the state in  FIG.  4 A ) and when in a state in which there is a sheet in the conveyance path, the light is transmitted (the state in  FIG.  4 B ). 
     As illustrated in  FIGS.  5 A and  5 B , the discharge detection flag  60  serving as a first pivotably moving member and the sheet width detection flag  63  serving as a third pivotably moving member that are moving pivotably in the sheet conveyance direction are provided between the fixing portion  5  and the discharge rollers  6 . Similar to the registration detection flag  30  described above, the discharge detection flag  60  and the sheet width detection flag  63  detect the sheet by having the conveyed sheet  20  abut thereagainst and by being pivoted. In other words, the light shielding portion  62  of the discharge detection flag  60  is switched so that a light of a photointerrupter  71  serving as a first detecting portion disposed on the electric board  7  described later is transmitted or shielded. With the above, the state of the sheet can be detected from a rotation state (a pivot state) of the discharge detection flag  60 . Similarly, a light shielding portion  65  of the sheet width detection flag  63  is switched so that a light of a photointerrupter  72  serving as a third detecting portion disposed on the electric board  7  described later is transmitted or shielded. With the above, the state of the sheet can be detected from a rotation state (a pivot state) of the sheet width detection flag  63 . 
     As illustrated in  FIG.  6   , a contact portion  61  of the discharge detection flag  60  is disposed in the vicinity of a middle portion in a width direction that is orthogonal to the sheet conveyance direction. Similar to the registration detection flag  30 , the discharge detection flag  60  performs a detection operation of whether there is a sheet by being pivoted in the sheet conveyance direction by having the contact portion  61  of the discharge detection flag  60  be in contact with the front edge of the sheet  20  in the conveyance direction and by having the sheet  20  push the contact portion  61 . A contact portion  64  of the sheet width detection flag  63  is disposed in the vicinity of an edge portion in the width direction that is orthogonal to the sheet conveyance direction. The sheet width detection flag  63  performs the sheet detection operation (the state illustrated in  FIG.  4 B ) described above when the width (the length in the width direction) of the sheet is large enough to abut against the contact portion  64 . Conversely, in a case in which the width of the sheet is small such that the sheet does not abut against the contact portion  64 , the sheet width detection flag  63  does not perform the sheet detection operation since the contact portion  64  does not come into contact with the sheet  20  even if the sheet  20  is conveyed thereto. 
     An example method of using detection results of the photointerrupters obtained through the detection flags will be described next. 
     In a case of a monochrome laser printer, after detecting the front edge of the sheet  20  with the registration detection flag  30 , formation of an image is started at a predetermined timing so that the position of the image, which is on the transfer portion  4  and which is to be transferred, with respect to the sheet  20  is adjusted. The adjustment is made since there is a variation in the positions of the front edges of the sheet  20  on the tray depending on how the user places the sheets  20  thereon. Accordingly, by starting formation of the image after the front edge  21  of the sheet  20  has been detected, regardless of the position of the sheet  20  placed on the tray, the image can be transferred onto the sheet at a uniform position in the sheet conveyance direction. Furthermore, in a case of a color laser printer, if formation of the image is started after the front edge of the sheet  20  has been detected, the image to be transferred will not reach the image transfer position at the timing at which the sheet  20  is conveyed to the image transfer position; accordingly, the conveyance speed of the sheet  20  is adjusted after the sheet has been detected so that the position at which the image is transferred onto the sheet is uniform. In either case, the transfer position of the image with respect to the sheet is adjusted through the detection of the front edge of the sheet with the registration detection flag  30 . 
     Subsequently, when the discharge detection flag  60  does not detect any sheet after a predetermine time has passed after the front edge  21  of the sheet  20  has been detected with the registration detection flag  30 , the discharge detection flag  60  determines that sheet jamming (paper jamming) has occurred and stops the conveyance operation. 
     Lastly, when the registration detection flag  30  detects a sheet  20  and the sheet width detection flag  63  also, in a similar manner, detects the sheet  20 , the sheet width detection flag  63  determines that a large-sized sheet that has a large size in the width direction has been conveyed. On the other hand, in a case in which the registration detection flag  30  detects the sheet  20  and in which the sheet width detection flag  63  does not detect any sheet, the sheet width detection flag  63  determines that a small-sized sheet that has a small size in the width direction compared with the large-sized sheet is conveyed. 
     As described above, the registration detection flag  30  and the discharge detection flag  60  uses information on the conveying timing of the sheet  20 , and the sheet width detection flag  63  uses information on whether there is a sheet  20  present. 
     As illustrated in  FIG.  6   , the image forming apparatus  1  according to the present embodiment includes, at a lower side of the apparatus, a transfer portion conveying unit  10  serving as a second unit and, at an upper side of the apparatus, a fixing portion discharge unit  11  serving as a first unit. The second unit is disposed upstream of the first unit in the sheet conveyance direction. The first unit and the second unit are fixed in a direction that is parallel to a portion in the sheet conveyance direction. In the present embodiment, the first unit and the second unit are fixed in the up-down direction and the vertical direction of the apparatus. The transfer portion conveying unit  10  serving as the second unit includes the conveyance roller  3 , the transfer portion  4 , and the registration detection flag  30  serving as the second pivotably moving member, which are illustrated in  FIG.  3   . The fixing portion discharge unit  11  serving as the first unit includes the fixing portion  5 , the discharge rollers  6 , the discharge detection flag  60  serving as the first pivotably moving member, and the sheet width detection flag  63  serving as the third pivotably moving member, which are illustrated in  FIG.  3   . 
     Referring next to  FIG.  7   , the photointerrupters and the electric board  7  serving as detecting portions corresponding to the detection flags will be described.  FIG.  7    is a perspective view of the inside of the printer viewed from the rear side. The electric board  7  includes, on the same plane, the photointerrupter  70  serving as the second detecting portion that detects the sheet conveyed at the transfer portion conveying unit  10 , and the photointerrupter  71  serving as the first detecting portion that detects the sheet conveyed at the fixing portion discharge unit  11 . Furthermore, in the present embodiment, the electric board  7  includes, on the same surface (on a board surface  80 ) as those of the photointerrupters  70  and  71 , the photointerrupter  72  serving as the third detecting portion that detects the sheet conveyed at the fixing portion discharge unit  11 . 
     The transfer portion conveying unit  10  includes the registration detection flag  30  (see  FIG.  3   ) serving as the second pivotably moving member pivoted by the conveyed sheet, and the photointerrupter  70  detects the sheet, which is conveyed at the transfer portion conveying unit, with the pivoting of the registration detection flag  30 . Herein, the photointerrupter  70  detects the front edge of the sheet in the conveyance direction through the registration detection flag  30 . The fixing portion discharge unit  11  includes the discharge detection flag  60  serving as the first pivotably moving member pivoted by the conveyed sheet, and the photointerrupter  71  detects the sheet, which is conveyed at the fixing portion discharge unit, through the discharge detection flag  60 . Herein, the photointerrupter  71  detects the front edge of the sheet in the conveyance direction through the discharge detection flag  60 . The fixing portion discharge unit further includes the sheet width detection flag  63  serving as the third pivotably moving member that is pivoted by the conveyed sheet at a position that is different from the position of the discharge detection flag  60 . The photointerrupter  72  detects the sheet that is conveyed at the fixing portion discharge unit  11  through the sheet width detection flag  63 . Herein, the size of the sheet in the width direction is detected through the sheet width detection flag  63 . 
     The transfer portion conveying unit  10  includes a second boss  39  that engages with a round hole  81  serving as a second board restricting portion of the electric board  7  and that serves as a second unit restricting portion that restricts the electric board. The second boss  39  extends from the transfer portion conveying unit  10  towards the electric board  7  side. The fixing portion discharge unit  11  includes a first boss  69  that engages with a slit (a slit-shaped hole)  82  serving as a first board restricting portion of the electric board  7  and that first unit restricting portion that restricts the electric board. Similar to the second boss  39 , the first boss  69  also extends from the fixing portion discharge unit  11  towards the electric board  7  side. 
     The electric board  7  includes, at a position that corresponds to the second boss  39  of the transfer portion conveying unit  10 , the round hole  81  that engages with the second boss  39  and that serves as the second board restricting portion that restricts the transfer portion conveying unit  10 . Furthermore, the electric board  7  includes, at a position that corresponds to the first boss  69  of the fixing portion discharge unit  11 , the slit  82  that engages with the first boss  69  and that serves as the first board restricting portion that restricts the fixing portion discharge unit  11 . 
     The electric board  7  is attached to the transfer portion conveying unit  10  and the fixing portion discharge unit  11 . The second boss  39  of the transfer portion conveying unit  10  is fitted to the round hole  81  of the electric board  7 , and the first boss  69  of the fixing portion discharge unit  11  is fitted to the slit  82  of the electric board  7 . Note that the round hole  81  and the slit  82  are both provided at substantially the middle in the width direction of the sheet. 
     Furthermore, as illustrated in  FIG.  3   , the board surface of the electric board  7  attached to the transfer portion conveying unit  10  and the fixing portion discharge unit  11  is substantially parallel to the sheet that is conveyed at the transfer portion conveying unit  10  and the fixing portion discharge unit  11 . In other words, among the conveyance paths of the sheet, the conveyance path that passes a portion next to (or the vicinity of) the electric board  7  is parallel to the board surface of the electric board, and a portion CH in the sheet conveyance direction is parallel to the board surface of the electric board. 
     Referring next to  FIG.  8   , the positional relationships between the round hole  81  and the slit  82  in the electric board  7  and the photointerrupters  70 ,  71 , and  72  will be described.  FIG.  8    is a diagram of the electric board  7  viewed from the front side of the printer. 
     As illustrated in  FIG.  8   , on the board surface  80  of the electric board  7 , the photointerrupter  70  corresponding to the registration detection flag  30  is provided in the vicinity of the round hole  81  corresponding to the transfer portion conveying unit  10 . On the board surface  80  of the electric board  7 , the photointerrupter  71  corresponding to the discharge detection flag  60  is provided in the vicinity of the slit  82  at the middle corresponding to the fixing portion discharge unit  11 . On the board surface  80  of the electric board  7 , the photointerrupter  72  corresponding to the sheet width detection flag  63  is, with respect to the photointerrupter  71 , provided at a position that is away from the slit  82  corresponding to the fixing portion discharge unit  11 . 
     The photointerrupters  70 ,  71 , and  72  include light emitting portions  70   a ,  71   a , and  72   a  and light receiving portions  70   b ,  71   b , and  72   b , respectively. A direction parallel to an optical axis  71   c  connecting the light emitting portion  71   a  and the light receiving portion  71   b  of the photointerrupter  71  corresponding to the discharge detection flag  60  is referred to as an X direction, and a direction orthogonal to the X direction parallel to the optical axis  71   c  is referred to as a Y direction. In the present embodiment, the X direction extending in the parallel direction and the Y direction that is a direction orthogonal to the parallel X direction are situated inside the plane of the electric board. As described later, the two directions inside the plane of the electric board are restricting directions that restrict the dispositions of the electric board as well. 
     Referring next to  FIG.  9   , a configuration of restricting the position of the electric board with a plurality of units will be described.  FIG.  9    is a cross-sectional view around the electric board  7  viewed from the front side of the printer. 
     The round hole  81  serving as the second board restricting portion included in the electric board  7  is fitted in the second boss  39  serving as the second unit restricting portion included in the transfer portion conveying unit  10  so that the dispositions of the transfer portion conveying unit  10  and the electric board  7  are restricted in the X direction parallel to and in the Y direction orthogonal to the optical axis (a straight line) connecting the light emitting portion and the light receiving portion. The slit  82  serving as the first board restricting portion included in the electric board is fitted to the first boss  69  serving as the first unit restricting portion included in the fixing portion discharge unit  11  so that the disposition of the fixing portion discharge unit  11  is restricted in the X direction parallel to and in the Y direction orthogonal to the optical axis (a straight line) connecting the light emitting portion and the light receiving portion. In other words, the disposition of the electric board  7  is restricted by the round hole  81  into which the second boss  39  is fitted and the slit  82  into which the first boss  69  is fitted. Furthermore, the electric board  7  restricts the transfer portion conveying unit  10  in the X direction and the Y direction, and restricts the fixing portion discharge unit  11  in the X direction. By having the fixing portion discharge unit  11  be fixed to the transfer portion conveying unit  10  in the Y direction parallel to a portion CH in the conveyance direction of the sheet, the fixing portion discharge unit  11  and the electric board  7  can be assembled with good accuracy even with only the restriction in the X direction. 
     Put in another way, in a state in which the round hole that is the second board restricting portion and the second boss that is the second unit restricting portion are engaged with each other, the disposition of the electric board is regulated in a parallel direction that is parallel to the optical axis connecting the light emitting portion and the light receiving portion of the first detecting portion. Furthermore, the disposition of the electric board is restricted in an orthogonal direction that is parallel to the portion CH in the sheet conveyance direction and that is orthogonal to the optical axis connecting the light emitting portion and the light receiving portion of the first detecting portion. Furthermore, in a state in which the slit that is the first board restricting portion and the first boss that is the first unit restricting portion are engaged with each other, the disposition of the electric board is restricted to a parallel direction that is parallel to the optical axis connecting the light emitting portion and the light receiving portion of the first detecting portion. Note that since the first board restricting portion is a slit-shaped hole that is provided so as to extend in the orthogonal direction that is parallel to the portion CH in the sheet conveyance direction and that is orthogonal to the optical axis connecting the light emitting portion and the light receiving portion of the first detecting portion, the disposition of the electric board is not restricted. In the present embodiment, positions of the first unit and the second unit in the orthogonal direction descried above are set by having the first unit and the second unit be fixed with a screw or the like. 
     With the above, since the fixing portion discharge unit  11  is restricted in the X direction on the upper side of the electric board  7 , the positions of the discharge detection flag  60  and the sheet width detection flag  63  in the X direction do not easily shift, and the discharge detection flag  60  and the sheet width detection flag  63  can accurately pass between the light emitting portion and the light receiving portion of the photointerrupter. If the position of the electric board  7  is set by the transfer portion conveying unit  10  alone, when the fixing portion discharge unit  11  shifts in the X direction relative to the transfer portion conveying unit  10 , the amount of shifting will be equivalent to the shift between the detection flag and the photointerrupter. When the amount of shifting is large, the discharge detection flag  60  and the sheet width detection flag  63  may become out of place with respect to the light emitting portion and the light receiving portion of the photointerrupter and there may be cases in which the sheet cannot be detected. 
       FIG.  12    is a diagram of the electric board  7  viewed from the front side of the printer front. When the fixing portion discharge unit  11  is shifted in the X direction by a shifting amount X relative to the transfer portion conveying unit  10 , the slit  82  of the electric board  7  is shifted in the X direction by the shifting amount X in a similar manner. Accordingly, the electric board  7  rotates about the fitting portion between the round hole  81  of the transfer portion conveying unit  10  and the second boss  39  of the transfer portion conveying unit  10 . When the rotational angel in the above case is θ, the photointerrupter  72  is also rotated by the same angle θ. 
     Referring to  FIG.  12   , L 0  denotes a distance in the electric board  7  between the second boss  39  of the transfer portion conveying unit  10  and the first boss  69  of the fixing portion discharge unit  11 , and L 1  denotes a distance in the electric board  7  between the photointerrupter  72  corresponding to the sheet width detection flag  63  and the second boss  39  of the transfer portion conveying unit  10 . With the calculation below, a moving amount X′ of the photointerrupter  72  when there is a shift in the X direction by the shifting amount X can be obtained. Note that regarding a moving amount Y of the photointerrupter  72  relative to a shift in the Y direction by a shifting amount Y is not considered herein since the direction is the same as a moving direction (pivoting direction) of the sheet width detection flag  63  corresponding to the photointerrupter  72 .
 
sin θ= X/L   0  
 
θ= A  sin( X/L   0 )
 
sin(θ+θ 1 )=( X   1   +X ′)/ L   1  
 
 X′=L   1 ×sin(θ+θ 1 )− X   1  
 
     On the other hand, the sheet width detection flag  63  provided in the fixing portion discharge unit  11  shifts together with the fixing portion discharge unit  11  in an integral manner by the shifting amount X; accordingly, the relative shift amount between the sheet width detection flag  63  and the photointerrupter  72  corresponding to the sheet width detection flag  63  is X-X′. 
     Supposing that a movement of a point A situated on a straight line connecting the second boss  39  and the first boss  69  is considered. A moving distance X A  of point A moving in the X direction is X=(L 0 /L A )×X A . It can be understood that X A  is proportional to X by a ratio between L 0  and L A . 
     In other words, for example, suppose L 0 :L A =10:9 holds true. Then, in the straight line connecting the second boss  39  and the first boss  69 , the distance L A  between the second boss  39  and point A is 0.9 times the length (a radius) of distance L 0  between the second boss  39  and the first boss  69 . In such a case, the shifting amount of the fixing portion discharge unit and the shifting amount of the photointerrupter are also  10 : 9 , and the relative shifting amount is X−X A =X×10%. The above is referred to as an attenuation factor of 10% with respect to the shifting amount of the fixing portion discharge unit. It has been understood that when the points that satisfy X−X′=X×10% are plotted, the attenuation factor 10% is, with respect to the lines (the dot and dash lines in  FIG.  12   ) tangent to the circle of L A  extended in the optical axis direction, the area away from the second boss  39  on the first boss  69  side. The above area is referred to as an attenuation-factor-10% area. 
     If the shifting amount of the fixing portion discharge unit with respect to the transfer portion conveying unit is 1 mm, then, the relative shifting amount between the flag and the photointerrupter in the X direction will be 0.1 mm when the photointerrupter is installed in the attenuation-factor-10% area. Accordingly, it can be said that there is almost no possibility of not being able to detect the sheet when shifted in the X direction. 
     The attenuation-factor-10% area of the photointerrupter  70  corresponding to the registration detection flag  30  will be discussed next. The detection of the sheet with the photointerrupter  70  through the registration detection flag  30  needs to be accurate in both the X direction and the Y direction. The area in which the shift in the X direction and the shift in the Y direction are both 10% is the area surrounded by a circle about the second boss  39  having a radius of L 0 ×0.1. When the radius, which is the shortest straight line connecting the second boss  39  and the photointerrupter  70 , is small, the attenuation-factor-10% area described above becomes narrow. Accordingly, when the photointerrupter  70  cannot be disposed inside the circle, it is desirable that electric elements (chip, capacitor, etc.) other than the photointerrupter  70  be removed and the photointerrupter  70  be disposed as close as possible to the second boss  39 . 
     In the present embodiment, the photointerrupter  70  that is the second detecting portion is provided in the vicinity of the round hole  81  that is the second board restricting portion of the electric board  7 . More specifically, there is no electric elements on the flat surface of the electric board  7  other than the second detecting portion (other than the photointerrupter  70 ) on a shortest straight line connecting the photointerrupter  70  and the boss  39 . 
     Similarly, the photointerrupter  71  that is the first detecting portion is provided in the vicinity of the slit  82  that is the first board restricting portion of the electric board  7 . More specifically, there is no electric elements on the flat surface of the electric board  7  other than the first detecting portion (other than the photointerrupter  71 ) on a shortest straight line connecting the photointerrupter  71  and the boss  69 . 
     Furthermore, since the attenuation factor of the shift becomes small when the radius L 0  becomes large, it is desirable that the electric elements be removed and the round hole  81  and the slit  82  be disposed close to a board edge surface of the electric board. 
     In the present embodiment, there is no electric element between the round hole  81  of the electric board  7  and an electric board edge surface  7   a  in the vicinity of the round hole  81 . Furthermore, there is no electric element between the slit  82  of the electric board  7  and an electric board edge surface  7   b  that is situated in the vicinity of the slit  82  and that is an electric board edge surface on the other side that opposes the electric board edge surface  7   a . The electric board  7  according to the present embodiment is configured in the above manner. With the above, the attenuation-factor-10% area described above can be made narrow, and even in a case in which one of the units becomes shifted relative to the other unit, the sheet detection with the photointerrupter through the flag can be performed accurately. Note that the electric board edge surface  7   a  situated in the vicinity of the round hole  81  and that is one of the edge surfaces of the electric board  7  is an edge surface on the upstream side in the sheet conveyance direction, and the electric board edge surface  7   b  situated in the vicinity of the slit  82  and that is the other edge surface of the electric board  7  is an edge surface on the downstream side in the sheet conveyance direction. 
     Referring next to  FIG.  10   , the positions of the photointerrupters provided on the electric board  7  will be described.  FIG.  10    is a diagram illustrating the inside of the printer viewed from the rear side. In  FIG.  10   , a straight line connecting the connections between the transfer portion conveying unit  10  and the fixing portion discharge unit  11  is depicted as a broken line B. Having the broken line B as a boundary, a transfer portion conveying unit area  13  is below the broken line B in  FIG.  10    and a fixing portion discharge unit area  12  is above the broken line. 
     The photointerrupter  70  corresponding to the registration detection flag  30  is situated in the transfer portion conveying unit area  13 . In other words, the photointerrupter  70  that is the second detecting portion is in the area  13  in the electric board  7  that includes the round hole  81  (see  FIG.  9   ) that is the second board restricting portion that restricts the transfer portion conveying unit. Meanwhile, the photointerrupter  73  corresponding to the discharge detection flag  60  and the photointerrupter  74  corresponding to the sheet width detection flag  63  are situated in the fixing portion discharge unit area  12 . In other words, the photointerrupter  71  that is the first detecting portion and the photointerrupter  72  that is the third detecting portion are in the area  12  in the electric board including the slit that is the first board restricting portion  82  (see  FIG.  9   ) that restricts the fixing portion discharge unit. 
     Furthermore, as illustrated in  FIGS.  4 A and  4 B , the photointerrupter  70  corresponding to the registration detection flag  30  is positioned between the contact portion  31  of the registration detection flag  30  and the second boss  39  that is the second unit restricting portion of the transfer portion conveying unit  10  in which the position of the transfer portion conveying unit  10  is regulated by the electric board  7 . 
     Furthermore,  FIGS.  11 A,  11 B, and  11 C  are diagrams illustrating one of connections  15  between the transfer portion conveying unit  10  and the fixing portion discharge unit  11 . As illustrated in  FIG.  11 A , the fixing portion discharge unit  11  is fastened by screws in the Y direction with respect to the transfer portion conveying unit  10 . As illustrated in  FIG.  11 B , the transfer portion conveying unit  10  includes screw fastening surfaces  16 , and as illustrated in  FIG.  11 C , the connections  15  between the transfer portion conveying unit  10  and the fixing portion discharge unit  11  are connected without any gap. Herein, in the conveyance direction in which the sheet is conveyed, the fixing portion discharge unit  11  that is the first unit is fixed downstream of the transfer portion conveying unit  10  that is the second unit. 
     As described above, the position of the electric board, which includes a plurality of detecting portions, is set relative to the plurality of units that correspond to the detecting portions. Furthermore, the positioning directions between the units are set to match the directions of the detecting portions. With the above, a sheet can be detected accurately with the plurality of detecting portions on the same board, which correspond to the plurality of units. 
     Note that in the embodiment described above, as illustrated in  FIG.  8   , the photointerrupter  71  corresponding to the discharge detection flag  60  is provided in the vicinity of the slit  82  at the middle corresponding to the fixing portion discharge unit  11 . Meanwhile, the photointerrupter  72  corresponding to the sheet width detection flag  63  is, with respect to the photointerrupter  71 , provided at a position that is away from the slit  82  corresponding to the fixing portion discharge unit  11 . In other words, the photointerrupter  71  corresponding to the discharge detection flag  60  has been exemplified as the first detecting portion that detects the edge portion in the sheet conveyance direction, and a configuration in which the above photointerrupter  71  is provided in the vicinity of the slit that is the first board restricting portion  82  has been exemplified; however, the configuration is not limited to the above exemplifications. The first detecting portion may be the photointerrupter  72  corresponding to the sheet width detection flag  63  that detects the size of the sheet in the width direction, and the above photointerrupter  72  may be provided in the vicinity of the slit that is the first board restricting portion  82 . Furthermore, the photointerrupter  71  corresponding to the discharge detection flag  60  may be the third detecting portion, and may be, with respect to the photointerrupter  72 , provided at a position that is away from the slit  82  corresponding to the fixing portion discharge unit  11 . From another viewpoint, the third detecting portion is disposed at the following position. First, there is a circle about the second boss that is the second unit restricting portion in which a radius thereof has a length that is 0.9 times a distance between the second unit restricting portion and the first boss that is the first unit restricting portion. There is a first boundary line that is tangent to the circle and that is orthogonal to a line connecting the second unit restricting portion and the first unit restricting portion. Furthermore, there is a second boundary line that is an edge portion of the electric board on the side on which a second fitting portion is provided. The third detecting portion is disposed between the first boundary line and the second boundary line. 
     Furthermore, in the embodiment described above, a configuration has been exemplified in which each member includes a pivotably moving member (a detection flag) that is pivoted by the conveyed sheet and in which each detecting portion detects the sheet by the pivoting of the pivotably moving member; however, the configuration is not limited to such a configuration. For example, openings may be provided at positions in the units corresponding to the detecting portions of the electric board and the sheet may be detected by the detecting portions through the openings. 
     Furthermore, in the embodiment described above, a configuration in which one detecting portion which detects the sheet conveyed at the transfer portion conveying unit that is the second unit is disposed, and in which two detecting portions which detect the sheet conveyed at the fixing portion discharge unit that is the first unit are disposed has been exemplified. However, the present disclosure is not limited to the above configuration. It is only sufficient that the electric board, the position of which is restricted by a plurality of units, includes at least one detecting portion corresponding to each unit. Furthermore, the number of detecting portions is not limited to three and can be provided accordingly according to the necessity. 
     Furthermore, in the embodiment described above, the transfer portion conveying unit has been exemplified as the second unit, and the fixing portion discharge unit as the first unit that is screwed to the transfer portion conveying unit has been exemplified; however, the configuration is not limited to the above. The configuration may be other combinations as long as the sheet is conveyed such as, for example, a configuration in which the feeding portion that separates and feeds the sheet and the conveying portion that conveys the sheet are connected to each other. 
     Furthermore, in the example embodiment described above, the printer has been exemplified as an image forming apparatus; however, the configuration is not limited to the above. For example, the image forming apparatus may be another image forming apparatus such as a copying machine or a facsimile machine, or a multi-functional apparatus that combines a plurality of the above functions. Similar effects can be obtained by applying the present disclosure to such image forming apparatuses. 
     In the embodiment described above, a configuration has been exemplified in which the image forming apparatus includes the plurality of units that convey the sheet, such as recording paper, that is a printing object; however, the present disclosure is not limited to the above. For example, a similar effect can be obtained when the present disclosure is used in an image forming apparatus that includes an image reading device that includes a plurality of units that convey a sheet, such as an original, that is the reading object. Alternatively, a similar effect can be obtained when the present disclosure is used in an image forming apparatus that includes a sheet processing device that includes a plurality of units that performs stapling or the like of sheets, such as recording paper, that are the recording object. 
     While the disclosure has been described with reference to example embodiments, it is to be understood that the invention is not limited to the disclosed example embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.