Patent Publication Number: US-2023161281-A1

Title: Light guide device, drum unit, image forming apparatus, and image reading apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2021-190949 filed on Nov. 25, 2021, the entire contents of which are incorporated herein by reference. 
     The present disclosure relates to a light guide device with a light guide member that guides light from a light source. 
     BACKGROUND 
     In an electrophotographic image forming apparatus, an electrostatic latent image is formed on a surface of a photoconductor drum by irradiating the surface of the photoconductor drum, which is uniformly charged, with laser light. The electrostatic latent image of the photoconductor drum is developed by a developing device using toner (developer). After the toner image of the photoconductor drum is transferred to a member on which transfer is performed, such as a sheet or an intermediate transfer belt, the surface of the photoconductor drum is irradiated with discharging light. This removes residual charge on the surface of the photoconductor drum. After the removal of the residual charge, the surface of the photoconductor drum is cleaned by a cleaning unit. 
     As a device for emitting the discharging light, a configuration is known that has a light source substrate with a light emitting element and a light guide member for guiding light emitted from the light emitting element to the photoconductor drum. 
     Conventionally, in an exposure device having a substrate with a light emitting element and an optical system for converging light from the light emitting element, a configuration is known in which the substrate is pressed by a pressing member to regulate the position of the substrate. 
     Incidentally, in order to stabilize the intensity of the discharging light irradiated on the surface of the photoconductor drum, the positioning accuracy between the light emitting element and the light-guiding member is important. If the positioning accuracy is low, the intensity of the discharging light varies. Even if the positional relationship between the light emitting element and the light guide member is appropriate, if the assembling accuracy of the light source substrate, the light guide member, and the support member supporting them is low, the intensity of the discharging light may vary. In the method of stacking and assembling multiple members such as the light source substrate, the light guide member, or other members on the support member, the assembly tolerances of each member are accumulated, and the assembly accuracy may be lowered by the accumulated tolerances. 
     SUMMARY 
     A light guide device according to one aspect of the present disclosure is provided with a support member, a light guide member, a first abutting part, and a cover member. The light guide member is supported by the support member and has a light incident surface on which light is incident. The first abutting part is provided on the light guide member and positions the light guide member at a first reference position predetermined in the support member by abutting on the abutted part of the support member. The cover member is attached to the support member and covers the light guide member. The cover member, while attached to the support member, has a first biasing part that biases the light guide member in an abutting direction where the first abutting part abuts the abutting part, and an engaging part that engages with the engaged part of the support member while the first biasing part generates a biasing force in the abutting direction. 
     A drum unit according to other aspects of the present disclosure is used mounted on an image forming apparatus. The drum unit is provided with a support member, a light guide member, a first abutting part, and a cover member. The support member rotatably supports the photoconductor drum. The light guide member is supported by the support member, has a light incident surface on which light is incident, and deflects the light incident on the light incident surface to emit the light toward the photoconductor drum. The first abutting part is provided on the light guide member and positions the light guide member at a first reference position predetermined in the support member by abutting on the abutted part of the support member. The cover member is attached to the support member and covers the light guide member. The cover member, while attached to the support member, has a first biasing part that biases the light guide member in an abutting direction where the first abutting part abuts the abutting part, and an engaging part that engages with the engaged part of the support member while the first biasing part generates a biasing force in the abutting direction. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a configuration of an image forming apparatus according to an embodiment of the present invention. 
         FIG.  2    shows an example of an image forming unit of the image forming apparatus. 
         FIG.  3    shows a perspective view of a drum unit of the image forming unit. 
         FIG.  4    shows a partially enlarged view showing a configuration of a right end of the drum unit. 
         FIG.  5    shows a partially enlarged view showing a configuration of a left end of the drum unit. 
         FIG.  6    shows an exploded perspective view of the drum unit, showing a cover member removed from a housing of the drum unit. 
         FIG.  7    shows a partially enlarged view schematically showing a mounting mechanism of the cover member. 
         FIG.  8    shows an exploded perspective view of the drum unit, showing a light guide member removed from the housing of the drum unit. 
         FIG.  9    shows a cross-sectional view of the drum unit cut in a vertical plane on a rear side of the light guide member. 
         FIG.  10    shows an enlarged cross-sectional view of a main part X in  FIG.  9   . 
         FIG.  11    shows an internal configuration of the right end of the drum unit. 
         FIG.  12    shows a perspective view showing a right side cover of the drum unit and its inner configuration. 
         FIG.  13    shows an enlarged cross-sectional view of a main part XIII in  FIG.  9   , showing the configuration of the right end of the light guide member and the periphery of a light source substrate. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will be described below with reference to drawings as appropriate. The embodiment described below is only one embodiment of the disclosure and does not limit its technical scope. Note that in the following explanation, a vertical direction D 1 , a front and rear direction D 2 , and a left and right direction D 3 , which are defined based on the installation condition (shown in  FIG.  1   ) in which an image forming apparatus  10  may be used. 
       FIG.  1    is a diagram showing the configuration of the image forming apparatus  10  according to an embodiment of the present disclosure. As shown in  FIG.  1   , the image forming apparatus  10  is equipped with a plurality of image forming units  1  through  4 , an intermediate transfer belt  5 , an optical scanner  6 , a secondary transfer roller  7 , a fixing device  8 , a paper output tray  9 , toner containers  21  through  24 , a paper feed cassette  31 , a conveyance path  32 , and a casing  33  for housing them. The image forming apparatus  10  is, for example, a color printer. The image forming apparatus  10  forms a color image or a monochrome image based on image data input from an information processing device such as a personal computer on a sheet (an example of a recording medium) such as paper fed from a paper feed cassette  31  along the conveyance path  32 . The image forming apparatus  10  may be a device having a printing function, for example, a copying machine or a fax machine. 
     The image forming units  1  through  4  are placed side by side along a running direction D 10  of the intermediate transfer belt  5 . The image forming units  1  through  4  constitute an image forming part of the so-called tandem system. The image forming unit  1  forms a toner image corresponding to a yellow color, the image forming unit  2  forms a toner image corresponding to a magenta color, the image forming unit  3  forms a toner image corresponding to a cyan color, and the image forming unit  4  forms a toner image corresponding to a black color. 
       FIG.  2    is a schematic diagram showing the configuration of the image forming unit  1 . As shown in  FIG.  2   , the image forming unit  1  includes a drum unit  18 , a developing device  13 , and a primary transfer roller  15 . The drum unit  18  is also equipped with a photoconductor drum  11 , a charging part  12 , a discharging part  14  (an example of the light guide device in this disclosure), and a cleaning unit  16 . The image forming unit  1  forms a toner image on the photoconductor drum  11  according to the electrophotographic method and transfers the toner image to the intermediate transfer belt  5 . Since the image forming units  2  through  4  have the same configuration as the image forming unit  1 , a description of them is omitted here. 
     The drum unit  18  is detachably mounted on the image forming apparatus  10 . In this embodiment, the drum unit  18  is mounted on the casing  33  by being inserted from the right side of the image forming apparatus  10  into the back side (left side) of the casing  33 . The drum unit  18  has a housing  19  that houses the photoconductor drum  11 , the charging part  12 , the discharging part  14 , and the cleaning unit  16 . The photoconductor drum  11  is rotatably supported on the housing  19 . The drum unit  18  also further includes a positioning mechanism  80  (see  FIG.  13   ). 
     The photoconductor drum  11  is arranged below the intermediate transfer belt  5 . The photoconductor drum  11  is an image carrier that carries an electrostatic latent image and a toner image. The charging part  12  is provided inside the housing  19  and is arranged under the photoconductor drum  11 . The charging part  12  has a charging roller  121  that charges the photoconductor drum  11  by power supplied from a power source (not shown). The surface of the photoconductor drum  11  is uniformly charged by the charging part  12 . The surface of the photoconductor drum  11  is irradiated with laser light by the optical scanner  6 . Thus, an electrostatic latent image based on the image data is formed on the surface of the photoconductor drum  11 . The developing device  13  has a developing roller  131  for developing the electrostatic latent image formed on the photoconductor drum  11  with toner (an example of developer). The developing device  13  is supplied with toner from the toner containers  21  through  24  of a color corresponding to the developing device  13 . 
     The primary transfer roller  15  transfers the toner image formed on the photoconductor drum  11  to the intermediate transfer belt  5 . The intermediate transfer belt  5  is an intermediate transfer member that runs above the photoconductor drums  11  of each image forming units  1  through  4 , and on which each color toner image formed on each photoconductor drum  11  is sequentially superimposed and transferred. The toner image transferred to the intermediate transfer belt  5  is transferred by a secondary transfer roller  7  (see  FIG.  1   ) to the sheet conveyed along the conveyance path  32 , and then the toner image transferred to the sheet is heated by the fixing device  8  and fixed to the sheet. 
     The cleaning unit  16  has a cleaning roller  161  for cleaning the photoconductor drum  11  after the transfer of the toner image. After the discharging part  14  removes the residual charge on the surface of the photoconductor drum  11 , the cleaning roller  161  removes the residual toner on the surface of the photoconductor drum  11 . 
     The discharging part  14  irradiates the area P 1  between the primary transfer roller  15  and the cleaning roller  161  on the outer surface of the photoconductor drum  11  with discharging light L 1  for discharging the photoconductor drum  11 . In other words, on the surface of the photoconductor drum  11 , the discharging part  14  irradiates, with discharging light L 1 , the area P 1  downstream of the primary transfer roller  15  in the rotation direction D 11  and upstream of the cleaning roller  161 . This removes the residual charge in the area P 1 . As a result, the removal of residual toner becomes easy and the so-called memory image of the photoconductor drum  11  is suppressed. 
       FIG.  3    is a perspective view of the drum unit  18 . The drum unit  18  rotatably supports the photoconductor drum  11  and is formed in a long shape in the left-right direction D 3  as shown in  FIG.  3   . The drum unit  18  is mounted on the inner frame or the like of the casing  33  with its longitudinal direction coinciding with the left and right direction D 3 . 
     As shown in  FIG.  3   , the housing  19  of the drum unit  18  has a housing body  20  (one example of a support member of the present disclosure) that is long in the left and right directions, a pair of side plates  201 ,  202 , and a side cover  63  (one example of a side member of the present disclosure). 
     The pair of side plates  201 ,  202  are provided on each of the longitudinal ends of the housing body  20 . The pair of side plates  201 ,  202  are integrally formed with the housing body  20 . As shown in  FIG.  4   , the side plate  201  is provided on the right side of the housing body  20 . As shown in  FIG.  5   , the side plate  202  is provided on the left side of the housing body  20 . Both ends of the photoconductor drum  11  are rotatably supported by the pair of side plates  201 , 202 . 
     The side cover  63  is provided at one end in the longitudinal direction of the housing body  20 . As shown in  FIG.  4   , the side cover  63  is attached to the outside (right side) side surface of the side plate  201  of the housing body  20 . The side cover  63  is mounted to cover the side of the side plate  201 . 
     The charging roller  121  and the cleaning roller  161  (see  FIG.  2   ) are also rotatably supported on the housing  19 . In this embodiment, the drum unit  18  is unitized by attaching the photoconductor drum  11 , the charging part  12 , the cleaning unit  16 , etc., to the housing  19 . 
     As shown in  FIG.  2   , the discharging part  14  is provided in the housing  19  of the drum unit  18 . The discharging part  14  emits the discharging light L 1  toward the surface of the photoconductor drum  11  as described above, and is an example of the light guide device in this disclosure. In this embodiment, the discharging part  14  is integrally provided with the drum unit  18 . 
       FIG.  6    is an exploded perspective view of the drum unit  18 , showing the cover member  62  removed from the housing  19  of the drum unit  18 .  FIG.  7    is a partially enlarged view schematically showing the mounting mechanism of the cover member  62 .  FIG.  8    is an exploded perspective view of the drum unit  18 , showing the light guide member  72  removed from the housing  19 . In  FIG.  6    and  FIG.  8   , the side cover  63  is not shown. 
     As shown in  FIG.  6   , the discharging part  14  includes a support frame  61 , a light guide member  72  (one example of a light guide member in this disclosure), the cover member  62  (one example of a cover member in this disclosure), a light source substrate  71  (one example of a light source substrate in this disclosure), and a pressing member  85  (one example of a first biasing part in this disclosure). 
     The support frame  61  supports the light guide member  72  and is formed integrally with the housing body  20 . The support frame  61  constitutes the upper portion of the housing body  20 . The support frame  61  is located on the rear side of the photoconductor drum  11  and is provided to bridge over the side plate  201  and the side plate  202  of the housing body  20 . Note that the support frame  61  needs not be formed integrally with the housing body  20 , but may be constructed independently of the housing body  20  and mounted on the upper part of the housing body  20 . 
     The light guide member  72  is supported by a support frame  61  at the top of the housing body  20 . In detail, the light guide member  72  is formed in a long shape in the longitudinal direction (left and right direction D 3 ) of the drum unit  18 . The light guide member  72  is formed in a rod shape by, for example, transparent acrylic resin. The light guide member  72  is longer than the photoconductor drum  11  and is arranged so that its longitudinal direction is parallel to the axial direction of the photoconductor drum  11 . 
     The cover member  62  is attached to the upper part of the housing body  20 . The cover member  62  is detachably attached to the support frame  61 . The cover member  62  is supported slidably in the left and right direction D 3  (sliding direction) with respect to the support frame  61 . The cover member  62  is attached to the support frame  61  with the light guide member  72  supported by the support frame  61 . In other words, the light guide member  72  is accommodated in the accommodation space formed between the cover member  62  and the support frame  61  by attaching the cover member  62  to the support frame  61 . Thus, the cover member  62  covers the light guide member  72  to block outside light. 
     Two engaging hooks  621  are formed on the cover member  62 . The engaging hook  621  is a hook that projects downward from the rear edge of the cover member  62  and bends to the right in a hook-like manner. Two engaging pieces  611  that can be engaged with the engaging hooks  621  are formed on the support frame  61 . The engaging piece  611  is a rectangular plate-like member projecting rearward from the rear end of the support frame  61 . The cover member  62  is arranged so that the engaging hook  621  is positioned on the left side of the engaging piece  611 , and then the cover member  62  is slid to the right side, so that the engaging hook  621  engages the engaging piece  611 . Thus, the cover member  62  is engaged with the support frame  61  to prevent it from coming off upward. 
     As shown in  FIG.  7   , an engaging hook  625  (an example of an engaging part in the present disclosure) is formed on the right end  624  of the cover member  62 . The right end  624  is the right end at the rear end of the cover member  62 . The engaging hook  625  projects rightward from the right end  624 . 
     The engaging hook  625  constitutes a snap-fit structure to the side plate  201 . The engaging hook  625  has an arm part  626  protruding to the right from a right end  624  and a hook-shaped hook part  627  formed at the tip of the arm part  626 . The hook part  627  is bent forward in a hook-like shape at the tip of the arm part  626 . The arm part  626  has flexibility to bend in the front and rear direction D 2  with respect to the cover member  62 , and has elasticity to bend in the pressing direction when pressed in the front and rear direction D 2  and to return to the original posture when the pressing is lost. 
     The side plate  201  is formed with an engaging piece  203  (an example of an engaged part in the present disclosure) that can be engaged with an engaging hook  625 . The engaging piece  203  is formed at the rear end of the side plate  201 . The engaging piece  203  is provided at a position corresponding to the engaging hook  625  in the side plate  201 . 
     When the cover member  62  is slid to the right with the engaging hook  621  engaged with the engaging piece  611 , the engaging hook  625  abuts on the engaging piece  203  of the side plate  201 . When the cover member  62  is further slid to the right side, the hook part  627  rides across the engaging piece  203  to be placed on the right side of the engaging piece  203  while the arm part  626  of the engaging hook  625  is deflected backward. In this state, the engaging hook  625  engages the engaging piece  203 . That is, the engaging hook  625  and the engaging piece  203  engage with respect to the left and right direction D 3 . In other words, the engagement direction of the engaging hook  625  and the engaging piece  203  coincides with the sliding direction of the cover member  62  with respect to the support frame  61 . Thus, the cover member  62  is engaged with the support frame  61  so that the cover member  62  cannot slide to the left. 
     As shown in  FIG.  6   , the pressing member  85  is provided on the support frame  61 . With the cover member  62  attached to the support frame  61 , the pressing member  85  elastically presses an end face  723  (input surface) of a left end  722  (one example of the other end of the present disclosure) in the left and right direction D 3  (longitudinal direction) of the light guide member  72  in the pressing direction D 31  (right direction). That is, with the light guide member  72  attached to the support frame  61  and the cover member  62  attached to the support frame  61 , the pressing member  85  applies a biasing force to the left end  722  to bias the light guide member  72  in the pressing direction D 31  (right direction). The pressing member  85  is, for example, an elastic member such as a silicone rubber, a sponge member or a spring. The pressing member  85  corresponds to the abutting direction in the present disclosure. 
     As shown in  FIG.  8   , a holding member  74  is formed at the left end of the support frame  61 . The holding member  74  projects upward from the upper surface of the support frame  61 . The holding member  74  supports the left end  722  of the light guide member  72  and has a support groove  741  that is open on the upper side. The left end  722  of the light guide member  72  is inserted into this support groove  741  and supported. 
       FIG.  9    is a cross-sectional view of the rear view when the drum unit  18  is cut in the vertical plane on the rear side of the light guide member  72 .  FIG.  10    is a partially enlarged view of the main part X in  FIG.  9   . As shown in  FIG.  10   , the pressing member  85  is placed on the left side of the holding member  74 , and more specifically, the pressing member  85  is placed in a compressed state between the holding member  74  and a left wall  628  of the cover member  62  (an example of the opposing portion of the present disclosure) with the cover member  62  attached to the support frame  61 . 
     The left wall  628  is a plate-like side wall extending downward from the left end of the upper surface of the cover member  62 . With the cover member  62  attached to the housing body  20 , the left wall  628  faces the end face  723  of the left end  722  of the light guide member  72 . 
     Since the pressing member  85  is provided in such a position, when the cover member  62  is slid to the right side to engage the engaging hook  625  (see  FIG.  7   ) with the engaging piece  203  (see  FIG.  7   ), the left wall  628  presses the pressing member  85  in the pressing direction D 31 . Thus, the pressing member  85  is compressed by the left wall  628 . The engaging hook  625  and the engaging piece  203  are engaged to maintain the compression state of the pressing member  85 . Since the pressing member  85  is arranged in this way, the compressed pressing member  85  can apply a biasing force to the left end  722  to press the light guide member  72  in the pressing direction D 31 . That is, the left end  722  of the light guide member  72  is pressed in the pressing direction D 31  by the restoring force of the pressing member  85 . 
     By the way, in order to stabilize the intensity of the discharging light L 1  emitted on the surface of the photoconductor drum  11  in the discharging part  14 , the positioning accuracy between the light emitting element  711  of the light source substrate  71  and an incident surface  77  of the light guide member  72  is important. If the positioning accuracy is low, the intensity of the discharging light L 1  varies. Even if the positional relationship between the light emitting element  711  and the incident surface  77  of the light guide member  72  is appropriate, if the assembly accuracy of the light source substrate  71 , the light guide member  72 , and the support member supporting them is low, the intensity of the discharging light L 1  may vary. In the conventional method of assembling multiple members such as the light source substrate  71 , the light guide member  72  and other members to the support member, the assembly tolerance of each member accumulates, and the assembly accuracy may be lowered by the accumulated tolerance. On the other hand, in the present embodiment, since the light guide member  72  and the light source substrate  71  are positioned as described later, it is possible to improve the positioning accuracy between the light emitting element  711  of the light source substrate  71  and the incident surface  77  of the light guide member  72 , and to improve the assembly accuracy of each member including the light source substrate  71  and the light guide member  72 . 
     In this embodiment, a pair of projections  76  (see  FIG.  8    for an example of the first abutting part of the present disclosure) provided on the light guide member  72 , described later, are positioned at the first reference position abutting on the side plate  201  (an example of the first reference position in this disclosure) by biasing the light guide member  72  in the pressing direction D 31  by the pressing member  85 . Thus, the light guide member  72  is stably held in the first reference position. 
       FIG.  11    shows the internal configuration of the right end of the drum unit  18 . In  FIG.  1   , the side cover  63  is not shown. As shown in  FIG.  11   , a holding hole  201 A is formed in the side plate  201  to hold the right end  721  of the other side (right side) of the light guide member  72  supported by the support frame  61 . When the right end  721  of the light guide member  72  is inserted into the holding hole  201 A, the right end  721  of the light guide member  72  is supported by the holding hole  201 A. 
     The light guide member  72  has a flat incident surface  77  (one example of the light incident surface of this disclosure) at the right end  721  (one example of one end of this disclosure) in the left and right direction D 3  (the longitudinal direction of the light guide member  72 ). The light from the light source substrate  71  is incident on the incident surface  77 . In addition, the light guide member  72  has an exit surface (not shown) that emits light in a direction crossing its longitudinal direction and toward the area P 1  in the photoconductor drum  11 . The exit surface is provided on the front side of the light guide member  72 . 
     In this embodiment, the front exit surface of the light guide member  72  is formed to have a semicircular or arc shape in a side view. The exit surface of the light guide member  72  is an arc-shaped curved surface (arc surface) extending along the longitudinal direction. 
     In the inside of the light guide member  72 , a plurality of transmission reflecting parts (not shown) are formed along its longitudinal direction. When light enters the inside of the light guide member  72  from the incident surface  77  and the light enters the transmission reflection part, a part of the incident light is reflected by the transmission reflection part and emitted forward from the exit surface as discharging light L 1  (see  FIG.  2   ). The discharging light L 1  is irradiated on the area P 1  (see  FIG.  2   ). 
       FIG.  12    is a perspective view showing the right side cover  63  of the drum unit  18  and its inner configuration. As shown in  FIG.  12   , the light source substrate  71  is attached to the inside surface of the side cover  63 , and in detail, is located on the upper part of the inside surface. The light source substrate  71  has a light emitting element  711  that emits light to neutralize the photoconductor drum  11 . The light emitting element  711  emits light toward the incident surface  77  of the light guide member  72  (see  FIG.  13   ). The light source substrate  71  is, for example, an LED light source in which a light emitting element  711  such as an LED element is mounted on the mounting surface of a rectangular substrate  712 . The light source substrate  71  is positioned between the side plate  201  (see  FIG.  11   ) and the side cover  63 . 
     The light source substrate  71  is provided on the inside surface of the side cover  63  so that the light emitting element  711  faces the incident surface  77 . The light emitted from the light emitting element  711  of the light source substrate  71  is incident on the incident surface  77  (see  FIG.  13   ) on one side in the longitudinal direction of the light guide member  72 . The light incident on the incident surface  77  travels inside the light guide member  72  to the other side in the longitudinal direction and exits from the exit surface while being reflected by the transmission reflecting part. 
     As shown in  FIG.  11   , the pair of projections  76  projecting in the vertical direction D 1  are provided near the right end  721  of the light guide member  72 . When the light guide member  72  is pressed to the right by the pressing member  85 , each projection  76  serves as a stopper to prevent the light guide member  72  from moving to the right from the prescribed first reference position. One projection  76  projects upward from the upper end of the light guide member  72 , and the other projection  76  projects downward from the lower end of the light guide member  72 . 
     The right end  721  of the light guide member  72  supported by the support frame  61  is inserted into the holding hole  201 A of the side plate  201 . In that state, the right end  721  is held by the holding hole  201 A. When the light guide member  72  is pushed in the right direction (pressing direction D 31 ) with the right end  721  held by the holding hole  201 A, the projection  76  abuts on the peripheral part of the holding hole  201 A (an example of the abutted part in the present disclosure). Thus, displacement of the light guide member  72  from the first reference position to the right side is regulated by the periphery of the projection  76  and the holding hole  201 A. That is, the light guide member  72  is positioned at the predetermined first reference position. In other words, the incident surface  77  of the right end  721  of the light guide member  72  is positioned at the predetermined first reference position. 
     As shown in  FIG.  11   , a positioning mechanism  80  is provided in the housing  19 . The positioning mechanism  80  positions the light emitting element  711  of the light source substrate  71  at a predetermined second reference position (an example of the second reference position in this disclosure) with respect to the incident surface  77  of the light guide member  72 . The second reference position is a position where the gap between the incident surface  77  of the light guide member  72  positioned at the first reference position and the light emitting element  711  becomes a predetermined reference interval. 
       FIG.  13    is an enlarged cross-sectional view of the main part XIII in  FIG.  9   , showing the configuration of the right end  721  of the light guide member  72  and the periphery of the light source substrate  71 . As shown in  FIG.  13   , the positioning mechanism  80  has an abutting pin  81  (one example of the second abutting part in the present disclosure) and an elastic member  82  (one example of the second biasing part in the present disclosure). 
     The abutting pin  81  is a part abutting on the mounting surface of the light emitting element  711  in the light source substrate  71 . The abutting pin  81  stands on the right side of the side plate  201 . The side plate  201  is provided with two abutting pins  81 . The abutting pins  81  are separated from each other in the vertical direction D 1 , and both the abutting pins  81  project vertically in the right direction from the right side surface of the side plate  201 . At the base end of the outer circumferential surface of the abutting pin  81  on the side plate  201  side, at least one or more ribs  83  extend in the projection direction of the abutting pin  81 . 
     A boss  92  is provided on the inside surface of the side cover  63 . A holding plate  91  made of sheet metal is fixed to the inside surface of the side cover  63  through the boss  92 . The holding plate  91  is fixed to the boss  92  by screws or the like. As shown in  FIG.  11    and  FIG.  13   , the elastic member  82  is attached to the surface of the holding plate  91 . The elastic member  82  is a member having elasticity such as silicone rubber, sponge member, and spring. The elastic member  82  is pressed when the side cover  63  is attached to the side plate  201 . The side cover  63  is contracted while attached to the side plate  201  to elastically press the light source substrate  71  to the incident surface  77  side (left side) of the light guide member  72 . In this embodiment, the elastic member  82  is a sponge member formed in a rectangular solid shape. One side (right side) surface of the elastic member  82  is fixed to the surface of the holding plate  91  by a bonding agent such as double-sided tape. On the other side (left side) surface of the elastic member  82 , the substrate  712  of the light source substrate  71  is fixed by a bonding agent such as double-sided tape. 
     Also, as shown in  FIG.  12   , the side cover  63  has two support arms  95  with hooks formed at the tips. The support arm  95  projects vertically from the inside surface of the side cover  63 , and the hook at its tip engages with the edge side of the substrate  712  of the light source substrate  71 . Thus, the light source substrate  71  can be displaced in the direction perpendicular to the inner side surface (the direction of contraction of the elastic member  82 ) within the contraction range of the elastic member  82 . 
     As shown in  FIG.  12   , two engagement holes  93  are formed in the substrate  712 . The engagement holes  93  are provided at positions corresponding to each abutting pin  81  (see  FIG.  13   ). Each engagement hole  93  is formed at a position separated in the vertical direction D 1  in the substrate  712 . When the side cover  63  is attached to the side plate  201 , the tip of the abutting pin  81  is inserted into the corresponding engagement hole  93 . Thus, the side cover  63  is attached and fixed to the side plate  201 , so that the rib  83  of the abutting pin  81  abuts against the periphery of the engagement hole  93  and presses the substrate  712  to the right side. On the other hand, the substrate  712  is pressed to the left side by receiving a biasing force from the elastic member  82 . Thus, the elastic member  82  is contracted by receiving the pressing force from the abutting pin  81 , and the light source substrate  71  is pressed to the light guide member  72  side (left side) by the elastic force generated by the contraction of the elastic member  82 . Thus, the light emitting element  711  of the light source substrate  71  is positioned at the second reference position. 
     By positioning the light source substrate  71  and the light guide member  72  in this way, positioning accuracy between the light emitting element  711  of the light source substrate  71  attached to the side cover  63  and the incident surface  77  of the light guide member  72  supported by the support frame  61  of the housing  19  can be improved. 
     As shown in  FIG.  12   , in the present embodiment, a connector board  96  on which connector members  97  and  98  are mounted is attached to the inside surface of the side cover  63 . The connector members  97  and  98  are members for relaying electric power supplied to the light emitting elements  711  of the light source substrate  71 , and are all mounted on the common substrate  99 . The connector board  96  is located at the bottom of the inside surface of the side cover  63 . In this embodiment, the mounting direction of the light source substrate  71  and the connector board  96  to the side cover  63  is the same as the mounting direction of the side cover  63  to the side plate  201  of the housing  19 . That is, both the light source substrate  71  and the connector board  96  are assembled along a direction (left and right direction D 3 ) perpendicular to the inside surface of the side cover  63 . 
     As described above, the mounting direction of the cover member  62 , which covers the light guide member  72  and positions the light guide member  72  at the first reference position, is also along the left and right direction D 3 . 
     In this way, the mounting direction of each member mounted on the side cover  63  is the same, and furthermore, the mounting direction of the cover member  62  with respect to the support frame  61  is the same, so that the assembly processing of each member becomes easy, and moreover, the assembly accuracy of the member after the assembly can be improved. 
     In the above example, the drum unit  18  is provided with the light source substrate  71 , the light guide member  72  and the positioning mechanism  80 , but the present disclosure is not limited to this configuration. For example, the present disclosure can be a light guide device that is not integrated into the drum unit  18  but includes the light source substrate  71 , the light guide member  72 , and the positioning mechanism  80 . Also, in the scanning unit of an image reading apparatus that reads an image of a document based on reflected light from an object to be irradiated, such as a document, the present disclosure can be a light guide device that directs light to the document by irradiating the reading surface of the document (irradiated surface), or as an image reading apparatus equipped with a scanning unit that includes such a light guide device.