Patent Publication Number: US-8988476-B2

Title: Exposure device and image forming apparatus having a light source positioning member and an elastically deformable board

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2013-121182 filed Jun. 7, 2013. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an exposure device and an image forming apparatus including the exposure device. 
     2. Summary 
     According to an aspect of the invention, an exposure device includes a board on which a light source for emitting a light beam is mounted and on which a circuit is disposed, a housing that contains an optical system for guiding the light beam, a positioning member that positions the light source relative to the housing in an optical axis direction by contacting a reference portion disposed around the light source, and a deformable portion disposed in a region of the board that is different from a region on which the circuit is disposed. The deformable portion urges the reference portion toward the positioning member by being elastically deformed when the board is attached to the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a partial exploded perspective view of an exposure device according to an exemplary embodiment of the present invention, illustrating a portion of the exposure device in which a light source is attached to a housing; 
         FIG. 2  is a plan view of a circuit board of the exposure device according to the exemplary embodiment of the present invention; 
         FIG. 3  is a partial sectional view of the exposure device according to the exemplary embodiment of the present invention, illustrating a portion of the exposure device in which the light source is attached to the housing; 
         FIG. 4  is a partial sectional view of the exposure device according to the exemplary embodiment of the present invention, illustrating a portion of the exposure device in which the light source is attached to the housing; 
         FIG. 5  is a partial sectional view of the exposure device according to the exemplary embodiment of the present invention, illustrating a portion of the exposure device in which the light source is attached to the housing; 
         FIG. 6  is a schematic view of the light source of the exposure device according to the exemplary embodiment of the present invention; 
         FIG. 7  is a schematic view illustrating the optical structure of the exposure device according to the exemplary embodiment of the present invention; 
         FIG. 8  is a perspective view illustrating the optical structure of the exposure device according to the exemplary embodiment of the present invention; 
         FIG. 9  is a schematic diagram illustrating an exposure device, a photoconductor drum, and other components of an image forming apparatus according to an exemplary embodiment of the present invention; 
         FIG. 10  is a schematic diagram illustrating toner image forming portions and other components of the image forming apparatus according to the exemplary embodiment of the present invention; and 
         FIG. 11  is a schematic diagram illustrating the image forming apparatus according to the exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 to 11 , an exposure device and an image forming apparatus according to exemplary embodiments of the present invention will be described. In the figures, an arrow H indicates the vertical direction, and an arrow W indicates a horizontal direction that is the width direction (of the image forming apparatus). 
     Overall Structure of Image Forming Apparatus 
       FIG. 11  is a schematic front view illustrating the overall structure of an image forming apparatus  10 . As illustrated in  FIG. 11 , the image forming apparatus  10  includes an image forming section  12 , a medium transport device  50 , and a postprocessing section  60 . The image forming section  12  forms an image on a sheet P, which is an example of a recording medium, by using an electrophotographic method. The medium transport device  50  transports the sheet P. The postprocessing section  60  performs postprocessing on the sheet P, on which an image has been formed. 
     The image forming apparatus  10  further includes a controller  70  and a power supply unit  80 . The controller  70  controls the aforementioned sections and the power supply unit  80 . The power supply unit  80  supplies electric power to the aforementioned sections and to the controller  70 . 
     The image forming section  12  includes toner-image forming portions  20 , a transfer device  30 , and a fixing device  40 . The toner-image forming portions  20  form toner images. The transfer device  30  transfers the toner images formed by the toner-image forming portions  20  to a sheet P. The fixing device  40  fixes the toner images transferred to the sheet P onto the sheet P. 
     The medium transport device  50  includes a medium feeding portion  52  and a medium output portion  54 . The medium feeding portion  52  feeds the sheet P to the image forming section  12 . The medium output portion  54  outputs the sheet P on which toner images have been formed. The medium transport device  50  further includes a medium reversing portion  56  and an intermediate transport portion (described below). The medium reversing portion  56  is used when the image forming apparatus  10  forms images on both sides of the sheet P. 
     The postprocessing section  60  includes a medium cooling portion  62 , a decurling device  64 , and an image inspection portion  66 . The medium cooling portion  62  cools the sheet P, to which the toner images have been transferred in the image forming section  12 . The decurling device  64  decurls the sheet P. The image inspection portion  66  inspects the toner images formed on the sheet P. The components of the postprocessing section  60  are disposed in the medium output portion  54  of the medium transport device  50 . 
     The components of the image forming apparatus  10  are contained in a housing  90 , except for a medium output tray  541  of the medium output portion  54  of the medium transport device  50 . In the present exemplary embodiment, the housing  90  has a two-part structure having a first housing  91  and a second housing  92 , which are arranged side by side in the width direction. Thus, it is possible to divide the image forming apparatus  10  into small units in the width direction when transporting the image forming apparatus  10 . 
     The first housing  91  contains the components of the image forming section  12  (excluding the fixing device  40  described below) and the medium feeding portion  52 . The second housing  92  contains the fixing device  40  of the image forming section  12 , the medium output portion  54  excluding the medium output tray  541 , the medium cooling portion  62 , the image inspection portion  66 , the medium reversing portion  56 , the controller  70 , and the power supply unit  80 . The first housing  91  and the second housing  92  are joined to each other by using fasteners, such as bolts and nuts (not shown). In this state, a connection opening  90 C 1  and a connection opening  90 C 2  are formed between the first housing  91  and the second housing  92 . The sheet P is transported from a transfer nip NT (described below) of the image forming section  12  to a fixing nip NF (described below) through the connection opening  90 C 1 . The sheet P is transported from the medium reversing portion  56  to the medium feeding portion  52  through the connection opening  90 C 2 . 
     Image Forming Section 
     As described above, the image forming section  12  includes the toner-image forming portions  20 , the transfer device  30 , and the fixing device  40 . The toner-image forming portions  20  form toner images of different colors. In the present exemplary embodiment, six toner-image forming portions  20  for a first special color (V), a second special color (W), yellow (Y), magenta (M), cyan (C), and black (K) are provided. The letters (V), (W), (Y), (M), (C), and (K) shown in  FIG. 10  represent these colors. The transfer device  30  transfers toner images of six colors, which have been first-transferred to a transfer belt  31  in an overlapping manner, from the transfer belt  31  to a sheet P at the transfer nip NT (as described in detail below). 
     In the present exemplary embodiment, the first special color (V) and the second specific color (W) are, for example, corporate colors of a user, which are likely to be more frequently used than other colors. 
     Toner Image Forming Portion 
     The toner-image forming portions  20  are basically the same except for the colors of toners they use. Therefore, in the following description, one of image forming units  14  will be described as an example. As illustrated in  FIG. 9 , the image forming unit  14  of the toner-image forming portion  20  includes a photoconductor drum  21 , a charger  22 , an exposure device  23 , a developing device  24 , a cleaning device  25 , and a charge eliminating device  26 . The photoconductor drum  21  is an example of an image carrying member, and the developing device  24  is an example of a developing unit. 
     Photoconductor Drum 
     The photoconductor drum  21  has a cylindrical shape, is grounded, and is rotated by a driving unit (not shown) around its own axis. A photosensitive layer is disposed on the surface of the photoconductor drum  21 . The photosensitive layer is, for example, negatively charged. As illustrated in  FIG. 10 , the photoconductor drums  21  for different colors are arranged along a straight line extending in the width direction in a front view. 
     Charger 
     As illustrated in  FIG. 9 , the charger  22  negatively charges the surface of (the photosensitive layer of) the photoconductor drum  21 . In the present exemplary embodiment, the charger  22  is a scorotron corona charger (non-contact charger). 
     Exposure Device 
     The exposure device  23  forms an electrostatic latent image on the surface of the photoconductor drum  21 . To be specific, the exposure device  23  irradiates the surface of the photoconductor drum  21 , which has been charged by the charger  22 , with a light beam L that is modulated in accordance with image data received from an image signal processor  71  (see  FIG. 11 ) of the controller  70 . An electrostatic latent image is formed on the surface of the photoconductor drum  21  as the exposure device  23  irradiates the surface with the light beam L. The exposure device  23  will be described below in detail. 
     Developing Device 
     The developing device  24  forms a toner image on the surface of the photoconductor drum  21  by developing the electrostatic latent image on the surface of the photoconductor drum  21  with a developer G including a toner. 
     Cleaning Device 
     The cleaning device  25  is a blade that scrapes off the toner remaining on the surface of the photoconductor drum  21  after the toner image has been transferred to the transfer device  30 . 
     Charge Eliminating Device 
     The charge eliminating device  26  eliminates static electricity by irradiating the photoconductor drum  21  with light after the transfer of the toner image. Thus, charges on the surface of the photoconductor drum  21  are eliminated. 
     Transfer Device 
     The transfer device  30  transfers (first-transfers) the toner images on the photoconductor drums  21  for different colors to the transfer belt  31  in an overlapping manner, and then transfers (second-transfers) the overlapping toner image to the sheet P. The transfer device  30  will be described below in detail. 
     Transfer Belt 
     As illustrated in  FIG. 10 , the transfer belt  31  is an endless belt that is looped over plural rollers  32  so as to form a certain shape. In the present exemplary embodiment, the transfer belt  31  forms an inverted obtuse triangular shape having a long side extending in the width direction in a front view. A roller  32 D illustrated in  FIG. 10 , which is one of the rollers  32 , functions as a driving roller that is driven by a motor (not shown) and that rotates the transfer belt  31  in the direction of an arrow A. 
     A roller  32 T, which is one of the rollers  32  illustrated in  FIG. 10 , functions as a tension roller that applies a tension to the transfer belt  31 . A roller  32 B, which is one of the rollers  32  illustrated in  FIG. 10 , functions as an opposing roller for a second-transfer roller (described below). A portion of the transfer belt  31  corresponding to a lower vertex of the inverted obtuse triangular shape is looped the roller  32 B. A portion of the transfer belt  31  corresponding to the upper side of the inverted triangular shape, which extends in the width direction, is in contact with lower portions of the photoconductor drums  21  for different colors from below. 
     First-Transfer Roller 
     First-transfer rollers  33  are disposed inside the loop of the transfer belt  31 . The first-transfer rollers  33 , which are examples of a transfer member, transfer the toner images on the photoconductor drums  21  to the transfer belt  31 . Each of the first-transfer rollers  33  is disposed so as to face a corresponding one of the photoconductor drums  21  with the transfer belt  31  therebetween. A transfer bias voltage having a polarity opposite to that of the toner is applied to the first-transfer rollers  33 . Due to the application of the transfer bias voltage, the toner images formed on the photoconductor drums  21  are transferred to the transfer belt  31 . 
     Second-Transfer Roller 
     The transfer device  30  further includes the second-transfer roller  34  that transfers the overlapping toner image on the transfer belt  31  to the sheet P. The second-transfer roller  34  and the roller  32 B are disposed with the transfer belt  31  therebetween, thereby forming the transfer nip NT between the second-transfer roller  34  and the transfer belt  31 . The sheet P is supplied to this transfer nip NT at an appropriate timing from the medium feeding portion  52 . A power supply unit (not shown) applies a transfer bias voltage, which has a polarity opposite to that of the toner, to the second-transfer roller  34 . Due to the application of the transfer bias voltage, the toner images are transferred from the transfer belt  31  to the sheet P passing through the transfer nip NT. 
     Cleaning Device 
     The transfer device  30  further includes a cleaning device  35  that cleans the transfer belt  31  after the second-transfer operation is finished. With respect to the rotation direction of the transfer belt  31 , the cleaning device  35  is disposed at a position on the downstream side of a region (the transfer nip NT) in which the second-transfer operation is performed and on the upstream side of the region in which the first-transfer operation is performed. The cleaning device  35  includes a blade  351  that scrapes off toner remaining on the surface of the transfer belt  31 . 
     Fixing Device 
     The fixing device  40  fixes the toner images, which have been transferred to the sheet P by the transfer device  30 , to the sheet P. In the present exemplary embodiment, the fixing device  40  fixes the toner images to the sheet P by heating and pressing the toner images at the fixing nip NF, which is formed between a pressure roller  42  and a fixing belt  411 , which is looped around plural rollers  413 . A roller  413 H, which is one of the rollers  413 , is a heating roller that contains, for example, a heater and that is rotated by a driving force transmitted from a motor (not shown). Thus, the fixing belt  411  is rotated in the direction of an arrow R. 
     The pressure roller  42  is rotated at the same peripheral velocity as the fixing belt  411  by a driving force transmitted from a motor (not shown). 
     Medium Transport Device 
     As illustrated in  FIG. 11 , the medium transport device  50  includes the medium feeding portion  52 , the medium output portion  54 , the medium reversing portion  56 , and the intermediate transport portion  58 . 
     Medium Feeding Portion 
     The medium feeding portion  52  includes containers  521  each containing a stack of sheets P. In the present exemplary embodiment, two containers  521  are disposed below the transfer device  30  so as to be arranged side-by-side in the width direction. 
     A medium feeding path  52 P is formed by plural transport roller pairs  522 , guides (not shown), and the like so as to extend from the containers  521  to the transfer nip NT, where the second-transfer operation is performed. The medium feeding path  52 P includes two turning portions  52 P 1  and  52 P 2  at which the direction of the medium feeding path  52 P is turned in the width direction. The entirety of the medium feeding path  52 P has a substantially S-shape extending upward to the transfer nip NT. 
     A feeding roller  523  is disposed in an upper portion of each of the containers  521 . Each of the feeding rollers  523  feeds an uppermost one of the sheets P stacked in the containers  521 . Transport roller pairs  522 S are two of the transport roller pairs  522  that are located on the most upstream side in the sheet-transport direction. The transport roller pairs  522 S function as separation rollers that separate the sheets P that are fed in an overlapping manner from the containers  521  by the feeding rollers  523 . A transport roller pair  522 R is one of the transport roller pairs  522  that is located at a position immediately upstream of the transfer nip NT in the sheet-transport direction. The transport roller pair  522 R causes the timing at which the toner image on the transfer belt  31  is moved to the transfer nip NT to match the timing at which the sheet P is transported to the transfer nip NT. 
     The medium feeding portion  52  also includes an auxiliary transport path  52 Pr. The auxiliary transport path  522 Pr extends from an opening  91 W, which is formed in a side surface of the first housing  91  opposite to a side surface adjacent to the second housing  92 , and joins the turning portion  52 P 2  of the medium feeding path  522 . The auxiliary transport path  52 Pr is used to feed a sheet P to the image forming section  12  when the sheet P is fed from an optional recording-medium feeding device (not shown), which is disposed adjacent to the opening  91 W in the first housing  91 . 
     Intermediate Transport Portion 
     As illustrated in  FIG. 10 , the intermediate transport portion  58  is disposed between the transfer nip NT of the transfer device  30  and the fixing nip NF of the fixing device  40 . The intermediate transport portion  58  includes plural belt transport members  581  each having an endless transfer belt, which is looped over rollers. 
     Air is sucked from the inside of the belt transport member  581  so as to produce a negative air pressure that attracts the sheet P to the surface of the transfer belt. In this state, the transfer belt rotate, and thereby the intermediate transport portion  58  transports the sheet P. 
     Medium Output Portion 
     As illustrated in  FIG. 11 , the medium output portion  54  outputs the sheet P, to which the toner image has been fixed by the fixing device  40  of the image forming section  12 , to the outside of the housing  90  through an output port  92 W, which is formed in a side surface of the second housing  92  opposite to a side surface adjacent to the first housing  91 . 
     The medium output portion  54  includes the medium output tray  541  for receiving the sheet P output from the output port  92 W. 
     This medium output portion  54  has a medium output path  54 P, along which the sheet P is transported from the fixing device  40  (fixing nip NF) to the output port  92 W. The medium output path  54 P is formed by a belt transport member  543 , plural roller pairs  542 , and guides (not shown). A roller pair  542 E is one of the roller pairs  542  that is disposed on the most downstream side in the sheet-output direction. The roller pair  542 E functions as an output roller that outputs the sheet P onto the medium output tray  541 . 
     Medium Reversing Portion 
     The medium reversing portion  56  includes plural roller pairs  561 . A reversing path  56 P is formed by the roller pairs  561 . A sheet P that has passed through the image inspection portion  66  is fed to the reversing path  56 P when a duplex image-forming mode is selected. The reversing path  56 P includes a branch path  56 P 1 , a transport path  56 P 2 , and a reversing path  56 P 3 . The branch path  56 P 1  branches off from the medium output path  54 P. The transport path  56 P 2  receives the sheet P from the branch path  56 P 1  and transports the sheet P to the medium feeding path  52 P. The reversing path  56 P 3 , which is provided in the transport path  56 P 2 , reverses the direction in which the sheet P is transported along the transport path  56 P 2  (transports the sheet P in a switchback manner), thereby flipping the sheet P over. 
     Postprocessing Section 
     The postprocessing section  60  includes the medium cooling portion  62 , the decurling device  64 , and the image inspection portion  66 , which are arranged in this order from the upstream side in the sheet-output direction along a portion of the medium output path  54 P of the medium output portion  54 , the portion being located on the upstream side of the branching portion of the branch path  56 P 1  in the sheet-output direction. 
     Medium Cooling Portion 
     The medium cooling portion  62  includes a heat absorbing device  621  that absorbs heat of the sheet P and a pressing device  622  that presses the sheet P against the heat absorbing device  621 . The heat absorbing device  621  is disposed above the medium output path  54 P, and the pressing device  622  is disposed below the medium output path  54 P. 
     The heat absorbing device  621  includes a heat-absorbing belt  6211  that is an endless belt, plural rollers  6212  that support the heat-absorbing belt  6211 , a heat sink  6213  disposed inside the loop of the heat-absorbing belt  6211 , and a fan  6214  for cooling the heat sink  6213 . 
     The outer peripheral surface of the heat-absorbing belt  6211  is in contact with the sheet P so that heat of the sheet P may be transferred to the heat-absorbing belt  6211 . A roller  6212 D, which is one of the rollers  6212 , functions as a driving roller that transmits a driving force to the heat-absorbing belt  6211 . The heat sink  6213  is in surface-contact with a predetermined portion of the inner peripheral surface of the heat-absorbing belt  6211  extending along the medium output path  54 P, and the heat-absorbing belt  6211  is slidable over the predetermined portion. 
     The pressing device  622  includes a pressing belt  6221 , which is an endless belt, and plural rollers  6222  that support the pressing belt  6221 . The pressing belt  6221  is looped over the rollers  6222 . The pressing device  622  presses the sheet P against the heat-absorbing belt  6211  (the heat sink  6213 ) and transports the sheet P in cooperation with the heat-absorbing belt  6211 . 
     Decurling Device 
     The decurling device  64  is provided on the downstream side of the medium cooling portion  62  in the medium output portion  54 . The decurling device  64  decurls the sheet P received from the medium cooling portion  62 . 
     Image Inspection Portion 
     An in-line sensor  661  of the image inspection portion  66  is disposed on the downstream side of the decurling device  64  in the medium output portion  54 . The in-line sensor  661  irradiates the sheet P with light and, on the basis of light reflected from the sheet P, detects the presence of a defect of a fixed tone image (and if present, the severity of the defect), such as nonuniform toner density, an image defect, a positional defect, or the like of a fixed toner image. 
     Image Forming Operation of Image Forming Apparatus 
     Next, the outline of an image forming operation performed on a sheet P by the image forming apparatus  10  and a postprocessing operation will be described. 
     As illustrated in  FIG. 11 , upon receiving an image forming command, the controller  70  activates the toner-image forming portions  20 , the transfer device  30 , and the fixing device  40 . Thus, as illustrated in  FIG. 10 , the photoconductor drums  21  of the image forming units  14  corresponding to the respective colors and a development roller  242  of the developing device  24  are rotated, and therefore the transfer belt  31  is rotated. Furthermore, the pressure roller  42  is rotated, and the fixing belt  411  is rotated. In synchronization with the rotations of these rollers and belts, the controller  70  activates the medium transport device  50  and other components. 
     The chargers  22  charge the photoconductor drums  21  for different colors while the photoconductor drums  21  are rotated. The controller  70  sends image data, which have been processed by the image signal processor, to the exposure devices  23 . The exposure devices  23  emit light beams L to the charged photoconductor drums  21  in accordance with the image data. As a result, electrostatic latent images are formed on the surfaces of the photoconductor drums  21 . The developing devices  24  develop the electrostatic latent images on the photoconductor drums  21  by using a developer. Thus, toner images of the first special color (V), the second special color (W), yellow (Y), magenta (M), cyan (C), and black (K) are formed on corresponding photoconductor drums  21 . 
     The color toner images formed on the photoconductor drums  21  are successively transferred to the rotating transfer belt  31  because the transfer bias voltage is applied to the first-transfer rollers  33 . As a result, an overlapping toner image, in which toner images of six colors overlap each other, is formed on the transfer belt  31 . The overlapping toner image is transported to the transfer nip NT as the transfer belt  31  rotates. 
     As illustrated in  FIG. 11 , the sheet P is fed to the transfer nip NT by the transport roller pair  522 R of the medium feeding portion  52  at the same time as the overlapping toner image is transported to the transfer nip NT. Because a transfer bias voltage is applied to the second-transfer roller  34  at the transfer nip NT, the overlapping toner image is transferred from the transfer belt  31  to the sheet P. 
     The intermediate transport portion  58  transports the sheet P, to which the toner image has been transferred, from the transfer nip NT of the transfer device  30  to the fixing nip NF of the fixing device  40 . The fixing device  40  applies heat and pressure to the sheet P passing through the fixing nip NF. Thus, the toner image on the sheet P is fixed to the sheet P. 
     The sheet P, which has passed through the fixing device  40 , is transported by the medium output portion  54  to the medium output tray  541  outside the device. During this time, the postprocessing section  60  performs a postprocessing operation as follows. First, the medium cooling portion  62  cools the sheet P, which has been heated in the fixing process. Then, the decurling device  64  decurls the sheet P. Then, the image inspection portion  66  inspects the toner image fixed to the sheet P in order to detect the presence of a defect of the fixed toner image (and if present, the severity of the defect), such as nonuniform toner density, an image defect, a positional defect, or the like of a fixed toner image. Subsequently, the sheet P is output to the medium output portion  54 . 
     When forming an image on a surface of the sheet P on which the image has not been formed (when performing a duplex image-forming operation), the controller  70  switches the transport path for the sheet P, which has passing through the image inspection portion  66 , from the medium output path  54 P of the medium output portion  54  to the branch path  56 P 1  of the medium reversing portion  56 . As a result, the sheet P is flipped over as the sheet P passes through the reversing path  56 P and is fed to the medium feeding path  52 P. An image is formed (and fixed) on the back surface of the sheet P through an image forming process the same as that performed on the front surface. An operation the same as that described above is performed on the back surface of the sheet P after an image has been formed on the front surface is performed. Then, the medium output portion  54  outputs the sheet to the medium output tray  541  outside the device. 
     Structure of Exposure Device 
     Next, the exposure device  23  will be described. 
     As illustrated in  FIG. 8 , the exposure device  23  includes a printed circuit board  330  (hereinafter simply referred to as “circuit board  330 ”). The circuit board  330  is attached to a housing  23 A (see  FIG. 9 ) of the exposure device  23 , and a light source  302  for emitting plural light beams L is mounted on the circuit board  330 . The circuit board  330  is an example of a board. A polygon mirror  306  is disposed between the light source  302  on the circuit board  330  and the photoconductor drum  21 , which is irradiated with the light beams L. The polygon mirror  306  is a component of an optical system  304  for deflecting and guiding the light beams L emitted from the light source  302 . 
     As illustrated in  FIG. 6 , the light source  302  is a surface emitting laser (so-called “VCSEL”) having plural emission points  308  for emitting the light beams L. To be specific, in the light source  302 , the emission points  308  are arranged two-dimensionally. For example, the light source  302  has two sets of emission points  308 , each set including six emission points  305  arranged along a straight line. The arrangement of the emission points  308  is adjusted so that light beams L are emitted to points that are separated from each other along straight lines having predetermined angles with respect to the main scanning direction and the sub-scanning direction. The light beams L, which have been modulated, are emitted from the emission points  308 , and the light beams L scan along scan lines that are different from each other with respect to the sub-scanning direction. The details of the light source  302  and the circuit board  330  will be described below. 
     As illustrated in  FIG. 8 , the polygon mirror  306  is a rotary body having a regular polygonal prism shape (in the present exemplary embodiment, a regular hexagonal prism shape). The polygon mirror  306  has six reflection surfaces  306 A on sides thereof and rotates in the direction of an arrow D around the axis of the regular hexagon as the polygon mirror  306  is driven by a motor (not shown). 
     The light beams L (only one of which is shown in  FIG. 8 ) emitted from the light source  302  are incident on the reflection surfaces  306 A. As the polygon mirror  306  rotates, the incident angles of the light beams L on the reflection surfaces  306 A continuously change, and therefore the light beams L are deflected by the reflection surfaces  306 A. Thus, the light beams L simultaneously scan the outer peripheral surface (exposure surface) of the photoconductor drum  21  in the main scanning direction (axial direction of the photoconductor drum  21 ). 
     A collimator lens  312  and a cylindrical lens  314  are arranged in this order along an optical path extending from the light source  302  to the polygon mirror  306 . The collimator lens  312  and the cylindrical lens  314  constitute the optical system  304  described above. The collimator lens  312  converts the light beams L, which are divergent when emitted from the emission points  308 , into parallel beams. The cylindrical lens  314  makes the light beams L converge in the sub-scanning direction and directs the light beams L toward the polygon mirror  306 . 
     In other words, the light beams L emitted from the light source  302  become parallel beams when the light beams L pass through the collimator lens  312 , and the light beams L converge at a focal point F, which is located downstream of the collimator lens  312  along the optical path, so as to intersect each other (see  FIG. 7 ). 
     As illustrated in  FIG. 8 , a pair of fθ lenses  320  are disposed on the downstream side of the polygon mirror  306  along the optical path. The fθ lenses  320  have an optical power that gathers the light beams L only in the main scanning direction. Moreover, the fθ lenses  320  cause the light beams L to scan the outer peripheral surface of the photoconductor drum  21  at the same scanning speed in the main scanning direction. A first cylindrical mirror  322  and a second cylindrical mirror  324  are disposed on the downstream side of the fθ lenses  320  along the optical path. The first cylindrical mirror  322  and the second cylindrical mirror  324  cause the light beams L to converge in the sub-scanning direction. 
     A reflection mirror  328  is disposed in an optical path between the first cylindrical mirror  322  and the second cylindrical mirror  324 . The reflection mirror  328  adjusts the angles at which the light beams L are incident on the second cylindrical mirror  324  in the sub-scanning direction. 
     To be specific, the pair of fθ lenses  320  adjust the light beams L, which have been deflected by the polygon mirror  306 , so that the light beams L scan the outer peripheral surface of the photoconductor drum  21  at the same scanning speed. 
     The first cylindrical mirror  322  and the second cylindrical mirror  324 , which have a power for gathering light in the sub-scanning direction, direct the light beams L toward the photoconductor drum  21  and focus the light beams L on the outer peripheral surface of the photoconductor drum  21 . 
     The first cylindrical mirror  322  and the second cylindrical mirror  324  are disposed so that the optical-side focal point of the first cylindrical mirror  322  and the image-side focal point of the second cylindrical mirror  324  coincide with each other (in other words, so that the optical path length between the first cylindrical mirror  322  and the second cylindrical mirror  324  is the same as the sum of the focal length of the first cylindrical mirror  322  and the focal length of the second cylindrical mirror  324 ). Thus, the positions of the reflection surfaces  306 A of the polygon mirror  306  and the positions on the outer peripheral surface of the photoconductor drum  21 , which is to be scanned by the laser beams L, have a relationship that is afocal and conjugate in the sub-scanning direction. 
     Light Source and Circuit Board 
     Next, the light source  302 , the circuit board  330 , and related components will be described in detail. 
     As illustrated in  FIG. 8 , the light source  302 , which emits the light beams L, are held by a holder  342  having a rectangular plate-like shape. The holder  342  holding the light source  302  is mounted on the circuit board  330 . The circuit board  330  has a rectangular shape extending in the main scanning direction (in the direction of an arrow S in  FIG. 8 ). The holder  342  is mounted on a portion of the circuit board  330  on one side in the main scanning direction (the right side in  FIG. 8 ). The holder  342  has a positioning surface  342 A, which is flat. The positioning surface  342 A surrounds the light source  302  and faces in the direction in which the light beams L are emitted. The positioning surface  342 A is an example of a reference portion. 
     As illustrated in  FIGS. 1 and 2 , attachment holes  352  are formed in the circuit board  330  on both sides of the holder  342  in the main scanning direction. The attachment holes  352  are used to attach the circuit board  330  to the housing  23 A of the exposure device  23 . The circuit board  330  has U-shaped cutout portions  354  each surrounding a corresponding one of the attachment holes  352 . To be specific, the cutout portions  354  having U-shapes are formed in the circuit board  330  so that the vertices of the cutout portions  354  face each other. 
     Deformable portions  356  (described below in detail) are portions of the circuit board  330  surrounded by the cutout portions  354  (which are hatched in  FIG. 2 ). When the circuit board  330  is attached to the housing  23 A, the deformable portions  356  become elastically deformed and generate restoring forces with which the deformable portions  356  urge the positioning surface  342 A against a positioning member  340  (as described below in detail). A circuit  358  is disposed on a region of the circuit board  330  that is different from a region in which the deformable portions  356  are disposed. 
     A connector  360  is attached to a portion of the circuit board  330  on the other side in the main scanning direction (the right side in  FIGS. 1 and 2 ). The connector  360 , which is an example of a connection member, is connectable to another connection member (not shown), which is, for example, a connector of a flexible printed circuit board. The connector  360  is attached to a surface of the circuit board  330  that is opposite to a mounting surface  330 A on which the holder  342  is mounted. The connector  360  has a rectangular-parallelepiped shape extending in the sub-scanning direction the direction of an arrow F in  FIG. 2 ). 
     An attachment hole  362  is formed in the circuit board  330  at a position adjacent to the connector  360 . The attachment hole  362  is used to attach the circuit board  330  to the housing  23 A. The attachment hole  362  is an example of an attachment portion. To be specific, the attachment hole  362  has a circular shape and is disposed at a position that is opposite the holder  342  with the connector  360  therebetween. The attachment hole  362  is located inside of an offset line  348 , which is an imaginary line on the circuit board  330  that surrounds the outer periphery of the connector  360  and that is separated from the outer periphery by 10 mm. 
     In other words, the phrase “a position adjacent to the connector  360 ” refers to a position in an area surrounded by the offset line  348  on the circuit board  330 , which is an imaginary line that surrounds the outer periphery of the connector  360  and that is separated from the outer periphery by 10 mm. 
     Housing 
     Next, the housing  23 A, to which the circuit board  330  is attached from the outside, will be described. 
     As illustrated in  FIG. 1 , a cylindrical portion  336  is disposed on a planar portion  338  of the housing  23 A, which faces outward. The cylindrical portion  336  connects the outer space of the housing  23 A to the inner space of the housing  23 A. The light beams Z emitted from the light source  302  enter the housing  23 A through the cylindrical portion  336 . 
     The positioning member  340  is disposed so as to surround the cylindrical portion  336 . The positioning member  340  positions the light source  302  in the optical axis direction by contacting the positioning surface  342 A disposed around the light source  302 . 
     The positioning member  340  includes three positioning portions  341 . Each of the positioning portions  341  is a cylindrical body attached to the housing  23 A and extending toward the circuit board  330 . The positioning portions  341  are arranged in the circumferential direction of the cylindrical portion  336  at regular intervals. When the circuit board  330  is attached to the housing  23 A, top surfaces  341 A of the positioning portions  341  contact the positioning surface  342 A. 
     Cylindrical bosses  346  are disposed on the planar portion  338  on both sides of the cylindrical portion  336  in the main scanning direction. The cylindrical bosses  346  face the deformable portions  356  of the circuit board  330  when the positioning surface  342 A contacts the top surfaces  341 A. A cylindrical boss  364  is disposed on the planar portion  338 . The cylindrical boss  364  contacts the attachment hole  362  of the circuit board  330  when the positioning surface  342 A contacts the top surfaces  341 A (see  FIG. 4 ). 
     To be specific, as illustrated in  FIGS. 3 and 4 , when the positioning surface  342 A contacts the top surfaces  341 A of the positioning portions  341  during the process of attaching the circuit board  330  to the housing  23 A, gaps are formed between the mounting surface  330 A, on which the holder  342  is mounted, and top surfaces  346 A of the bosses  346 . In this state, the mounting surface  330 A contacts a top surface  364 A of the boss  364 . 
     Then, the circuit board  330  is attached to the housing  23 A by inserting screws  368  into the attachment hole  352  and screwing the screws  368  into the bosses  346  and by inserting a screw  370  into the attachment hole  362  and screwing the screw  370  into the boss  364 . 
     As described above, when the positioning surfaces  342 A contact the top surfaces  341 A of the positioning portions  341 , gaps are generated between the mounting surface  330 A and the top surfaces  346 A of the bosses  346 . Therefore, as illustrated in  FIG. 5 , when the screws  368  are screwed into the bosses  346 , the deformable portions  356  become elastically deformed and the top surfaces  346 A of the bosses  346  contact the peripheries of the attachment holes  352 . 
     CONCLUSION 
     The deformable portion  356  is elastically deformable, because U-shaped cutout portions surround the attachment holes  352  in the circuit board  330 . When the deformable portions  356  become elastically deformed, restoration forces are generated, and the restoration forces urge the positioning surface  342 A toward the top surfaces  341 A of the positioning portions  341 . The circuit  358  is disposed on a region of the circuit board  330  that is different from a region in which the deformable portions  356  are disposed. Therefore, as compared with a case where a circuit board is attached to a housing by using an independent attachment member while causing a circuit on the circuit to be deformed, it is possible to suppress damage to the circuit  358  on the circuit board  330  and it is possible to position the light source  302  with a higher accuracy relative to the housing  23 A in the optical axis direction of the light source  302  by using a simple structure. 
     Because the light source  302  may be positioned with a higher accuracy in the optical axis direction, it is possible to form a toner image at a predetermined position on the outer peripheral surface of the photoconductor drum  21  (and therefore displacement of the image is suppressed). 
     The light source  302  is a surface emitting laser (so-called “VCSEL”) having the plural emission points  308  for emitting the light beams L. Because the emission surface of the light source  302  is inclined, there is a difference (focus difference) between the optical path length from one of the emission points  308  located in one end portion of the light source  302  to the outer peripheral surface of the photoconductor drum  21  and the optical path length from one of the emission points  308  located at the other end portion to the outer peripheral surface of the photoconductor drum  21 . However, as described above, because the accuracy of positioning of the light source  302  in the optical axis direction is increased, the inclination of the emission surface is reduced. As a result, it is possible to reduce the difference in the optical path length between the emission points to the outer peripheral surface of the photoconductor drum  21 . 
     The position of the circuit board  330  may be changed when another connection member is connected to or disconnected from the connector  360 . If the change in the position is not corrected, the emission points  308  may become inclined or may become displaced from desired positions. In this case, the emission surface of the light source  302  becomes inclined, and therefore a difference (focus difference) arises between the optical path length from one of the emission points  308  located in one end portion of the light source  302  to the outer peripheral surface of the photoconductor drum  21  and the optical path length from one of the emission points  308  located at the other end portion to the outer peripheral surface of the photoconductor drum  21 . With the present embodiment, such a difference is suppressed, because the circuit board  330  is attached to the housing  23 A by using the attachment hole  362  formed at a position adjacent to the connector  360 . 
     The present invention is not limited to the exemplary embodiments described above. It is clear for a person having ordinary skill in the art that these exemplary embodiments may be modified in various ways within the spirit and scope of the present invention. For example, in the exemplary embodiments described above, the deformable portions  356  are formed by cutting the circuit board  330  in U-shapes. Alternatively, the deformable portions  356  may be formed by making the thicknesses of portions of the circuit board  330  be smaller than other portions. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.