Patent Publication Number: US-2021173323-A1

Title: Optical scanning device and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an optical scanning device and an image forming apparatus such as a copy machine, a multifunction peripheral, a printer, or a facsimile machine. 
     Description of the Background Art 
     Generally, in optical scanning devices, to take a main scanning start time of an light beam emitted from a light source (for example, a laser diode element) and deflection-scanned by a deflection-scanning component (for example, a rotary polygon mirror) in a predetermined main scanning direction, the optical scanning device receives, by using a beam detector, the light beam at a time before the start of the main scan and outputs a beam detection signal from the beam detector indicating the time before the start of the main scan. In many of such optical scanning devices, the emission side of the light source and the light receiving side of the beam detector face a longitudinal direction of an fθ lens that is longest in the main scanning direction and emits a light beam deflection-scanned by a deflection-scanning component. In addition, the light source and the beam detector are often provided on one side of the fθ lens in the longitudinal direction of the housing (as in, for example, Japanese Unexamined Patent Publication No. 2017-227739), or provided on both sides. 
     In such an optical scanning device, wasted space (for example, space between the light source and the deflection-scanning component) is easily created, which leads to an increase in the size of the housing. Therefore, a decrease in the size of the housing is desired. 
     Hence, an object of the present invention is to provide an optical scanning device and an image forming apparatus that can have a housing with a decreased size. 
     SUMMARY OF THE INVENTION 
     In order to solve the above problem, the optical scanning device according to the present invention is an optical scanning device that includes a light source and a beam detector for taking the main scanning start time of a light beam emitted from the light source and deflection-scanned in a predetermined main scanning direction by a deflection-scanning component. On the light source and the beam detector, the emission side of the light source and the light receiving side of the beam detector face the light-incident side of an fθ lens, which is longest in the main scanning direction. The light source is arranged on the upstream side in the main scanning direction and the beam detector is arranged on the downstream side in the main scanning direction. Alternatively, the beam detector is arranged on the upstream side in the main scanning direction and the light source is arranged on the downstream side in the main scanning direction. Further, the image forming apparatus according to the present invention includes the optical scanning device of the present invention. 
     According to the present invention, it is possible to decrease the size of the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of an image forming apparatus according to the present embodiment as viewed from the front. 
         FIG. 2  is a perspective view of the front side of the optical scanning device of the image forming apparatus illustrated in  FIG. 1  as viewed from the upper right. 
         FIG. 3  is a perspective view of the back side of the optical scanning device illustrated in  FIG. 2  as viewed from the upper left. 
         FIG. 4  is a perspective view of the optical scanning device illustrated in  FIG. 2 , in which the upper lid is removed, as viewed from above on the front side. 
         FIG. 5  is a plan view showing the optical scanning device shown in  FIG. 4 . 
         FIG. 6  is an exploded perspective view illustrating a state in which the lower lid of the optical scanning device is removed. 
         FIG. 7  is a perspective view showing an example of a deflection-scanning unit in an optical scanning device. 
         FIG. 8A  is a plan view illustrating an example of the configuration of an optical system in an optical scanning device. 
         FIG. 8B  is a front view illustrating an example of the configuration of an optical system in an optical scanning device. 
         FIG. 9  is a plan view illustrating another example of the configuration of an optical system in an optical scanning device. 
         FIG. 10  is a plan view illustrating an example of the positional relationship between the light source and the beam detector in the optical scanning device according to the second embodiment. 
         FIG. 11  is a plan view showing another example of the positional relationship between the light source and the beam detector in the optical scanning device according to the second embodiment. 
         FIG. 12A  is a plan view showing an example of the positional relationship between the light source and the beam detector in the optical scanning device according to the third embodiment. 
         FIG. 12B  is a front view showing an example of the positional relationship between the light source and the beam detector in the optical scanning device according to the third embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. The names and functions of these parts are the same. Therefore, the detailed description of these parts will not be repeated. 
     Image Forming Apparatus 
       FIG. 1  is a schematic cross-sectional view of the image forming apparatus  100  according to the present embodiment as viewed from the front. In  FIG. 1 , reference numeral X represents a depth direction, reference numeral Y represents a left and a right direction (width direction), and reference numeral Z represents an up and a down direction (height direction). 
     The image forming apparatus  100  according to the present embodiment is a monochrome image forming apparatus. The image forming apparatus  100  performs an image forming process according to image data read by the image reading device  1  or image data transmitted from outside. It is noted that the image forming apparatus  100  may also be a color image forming apparatus that forms multicolor and monochromatic images on the paper P. 
     The image forming apparatus  100  includes a document feeder  108  and an image forming apparatus main body  110 . The image forming apparatus main body  110  is provided with an image forming unit  102  and a paper conveying system  103 . 
     The image forming unit  102  includes an optical scanning device  200  (optical scanning unit), a developing unit  2 , a photoreceptor drum  3  that acts as an electrostatic latent image carrier, a cleaning unit  4 , a charging device  5 , and a fixing unit  7 . Further, the paper conveying system  103  includes a paper feed tray  81 , a manual paper feed tray  82 , a discharge roller  31 , and a discharge tray  14 . 
     An image reading device  1  for reading an image of the document G is provided on the upper part of the image forming apparatus main body  110 . The image reading device  1  includes a document placing table  107  on which the document G is placed. Further, a document feeder  108  is provided on the upper side of the document placing table  107 . In the image forming apparatus  100 , the image of the document G read by the image reading device  1  is sent to the image forming apparatus main body  110  as image data, and the image is recorded on the paper P. 
     The image forming apparatus main body  110  is provided with a paper conveyance path S 1 . The paper feed tray  81  or the manual paper feed tray  82  supplies the paper P to the paper conveyance path S 1 . The paper conveyance path S 1  guides the paper P to the discharge tray  14  via the transfer roller  10  and the fixing unit  7 . The fixing unit  7  heats and fixes the toner image formed on the paper P onto the paper P. Pickup rollers  11   a  and  11   b , conveyance roller  12   a , registration roller  13 , transfer roller  10 , heat roller  71  and pressure roller  72  in the fixing unit  7 , and discharge roller  31  are arranged in the vicinity of the paper conveyance path S 1 . 
     In the image forming apparatus  100 , the paper P supplied by the paper feed tray  81  or the manual paper feed tray  82  is conveyed to the registration roller  13 . Next, the paper P is conveyed to the transfer roller  10  by the registration roller  13  at a time at which the paper P is aligned with the toner image on the photoreceptor drum  3 . The toner image on the photoreceptor drum  3  is transferred onto the paper P by the transfer roller  10 . After that, the paper P passes through the heat roller  71  and the pressure roller  72  in the fixing unit  7 , and is discharged onto the discharge tray  14  via the conveyance roller  12   a  and the discharge roller  31 . When an image is formed not only on the front surface of the paper P but also on the back surface, the paper P is conveyed from the discharge roller  31  to the reverse paper conveyance path S 2  in the opposite direction. The front and back of the paper P are reversed and the paper P is again guided to the registration roller  13  via the reverse transfer rollers  12   b . Then, after a toner image is formed and fixed on the back surface in the same manner as on the front surface, the paper P is discharged toward the discharge tray  14 . 
     Optical Scanning Device 
       FIG. 2  is a perspective view of the front side of the optical scanning device  200  in the image forming apparatus  100  illustrated in  FIG. 1  as viewed from the upper right.  FIG. 3  is a perspective view of the back side of the optical scanning device  200  illustrated in  FIG. 2  as viewed from the upper left.  FIG. 4  is a perspective view of the optical scanning device  200  illustrated in  FIG. 2 , in which the upper lid  202  is removed, as viewed from above on the front side.  FIG. 5  is a plan view illustrating the optical scanning device  200  shown in  FIG. 4 .  FIG. 6  is an exploded perspective view illustrating a state in which the lower lid  204  of the optical scanning device  200  is removed.  FIG. 7  is a perspective view illustrating an example of the deflection-scanning unit  220  in the optical scanning device  200 .  FIGS. 8A and 8B  are a plan view and a front view, each respectively illustrating an example of the configuration of the optical system in the optical scanning device  200 . Further,  FIG. 9  is a plan view illustrating another example of the configuration of the optical system in the optical scanning device  200 . In  FIGS. 2 to 9  and in  FIGS. 10 to 12B  described later, reference numeral X represents the main scanning direction (longitudinal direction of the fθ lens  231 ), reference numeral Y represents the direction orthogonal to both the main scanning direction X and the direction of the rotational axis (height direction H) of the deflection-scanning component  223 , and the reference numeral H represents the direction of the rotational axis (height direction) of the deflection-scanning component  223 . 
     The optical scanning device  200  includes a housing  201 , an incident optical system  210 , a deflection-scanning unit  220  (deflection scanner), and an emission optical system  230 . 
     The incident optical system  210  includes a light source  211  (laser diode element), a collimator lens  212 , an aperture component  213 , a cylindrical lens  214 , and a light source reflecting mirror  215 . The light source  211  emits a light beam L (laser beam). The collimator lens  212  exposes the aperture component  213  to the light beam L from the light source  211  as substantially parallel light. The aperture component  213  narrows the light beam L from the collimator lens  212  and exposes the cylindrical lens  214  to the light beam L. The cylindrical lens  214  causes the light beam L from the aperture component  213  to converge only in the sub-scanning direction and focuses the light beam L on a reflective surface  223   a  of the deflection-scanning component  223  (polygon mirror) via the light source reflecting mirror  215 . The light source reflecting mirror  215  guides the light beam L from the cylindrical lens  214  to a reflective surface  223   a  of the deflection-scanning component  223  (polygon mirror). 
     The deflection-scanning unit  220  includes a deflection-scanning substrate  221 , a deflection-scanning motor  222  (polygon motor), and a deflection-scanning component  223  (rotary polygon mirror (polygon mirror)). The deflection-scanning substrate  221  is attached to the flat surface (upper surface) side of the lower lid  204  by a plurality of attachment components (screws) SC. A deflection-scanning motor  222  is provided on the deflection-scanning substrate  221 . A deflection-scanning component  223  is attached to the rotating shaft  222   a  of the deflection-scanning motor  222 . The deflection-scanning component  223  deflection-scans the light beam L from the light source reflecting mirror  215  in a predetermined main scanning direction X 1 . 
     The emission optical system  230  includes an fθ lens  231 , a beam-detection reflecting mirror  232 , a beam detection lens  233  (focusing lens), and a beam detector  234  (beam detection sensor (BD sensor)). 
     The fθ lens  231  has a shape that is longest in the main scanning direction X 1 . The fθ lens  231  causes incidence of the light beam L that was deflection-scanned in the main scanning direction X 1  (longitudinal direction W) by the deflection-scanning component  223 . The beam-detection reflecting mirror  232  guides the light beam L deflection-scanned by a reflective surface  223   a  of the deflection-scanning component,  223  to the beam detection lens  233 . 
     Also, considering the detection accuracy of the beam detector  234 , it is necessary to make the first optical path length from the deflection-scanning component  223  to the scanning object (photoreceptor drum  3 ) equal to or substantially equal to the second optical path length from the deflection-scanning component  223  to the beam detector  234 , thereby to make the beam diameter of the light beam L exposed by the photoreceptor drum  3  equal to or substantially equal to the beam diameter of the light beam L exposed by the beam detector  234 . However, in this example, the first optical path length is longer than the second optical path length. Therefore, the light beam L from the beam-detection reflecting mirror  232  is focused on the beam detector  234  by using the beam detection lens  233 . As a result, even if the first optical path length is longer than the second optical path length, the beam diameter of the light beam L in the photoreceptor drum  3  and the beam diameter of the light beam L in the beam detector  234  are made equal or substantially equal. The beam detection lens  233  can tolerate a certain degree of deviation of the optical axis of the light beam L. 
     In order to take the main scanning start time (image writing start time) of the light beam L, the beam detector  234  receives the light beam L at a time before the start of the main scan and outputs a beam detection signal (BD signal) indicating the time before the start of the main scan. The beam detector  234  is an optical sensor (BD sensor) that acts as a synchronization detection element. In the present embodiment, the beam detector  234  uses the synchronization signal (BD signal) obtained by detecting the output signal from the beam detector  234  to adjust the time of the scanning start position of image recording on the surface of the photoreceptor drum  3 . The optical scanning device  200  further includes a substrate  240  (a substrate for the light source and the beam detector). A light source  211  and a beam detector  234  are provided on the substrate  240 . 
     The housing  201  has a bottom plate  201   a  with a rectangular shape and four side plates  201   b  to  201   e  surrounding the bottom plate  201   a . The housing  201  is provided with a deflection-scanning chamber  203  (see  FIGS. 4 to 6 ) that encloses the deflection-scanning unit  220 . An opening  203   a  (see  FIG. 6 ) is provided in a portion corresponding to the deflection-scanning chamber  203  in the bottom plate  201   a . The opening  203   a  is closed by the lower lid  204 . The lower lid  204  is attached to the bottom surface (lower surface) side of the bottom plate  201   a  by a plurality of attachment components (screws) SC. A deflection-scanning unit  220  is arranged on the lower lid  204 , and the deflection-scanning unit  220  is housed in the deflection-scanning chamber  203  by attaching the lower lid  204  to the bottom plate  201   a.    
     The light beam L reflected by the light source reflecting mirror  215  is incident on the inside of the deflection-scanning chamber  203  through the first window  203   b  (see  FIG. 5 ) formed in the deflection-scanning chamber  203 . Further, the light beam L scanned by the deflection-scanning component  223  is emitted to the outside of the deflection-scanning chamber  203  through the first window  203   b . A first dustproof glass plate  235  (transparent body) is provided in the first window  203   b . As a result, it is possible to effectively prevent unnecessary substances such as dust from entering into the deflection-scanning chamber  203 . Further, the light beam L that has passed through the fθ lens  231  is emitted to the outside of the housing  201  through the second window  201   f  formed in the side plate  201   e  of the housing  201  on the side of the fθ lens  231 . A second dustproof glass plate  236  (transparent body) is provided in the second window  201   f . As a result, it is possible to effectively prevent unnecessary substances such as dust from entering into the housing  201 . 
     The substrate  240  is a flat plate shaped, printed substrate that has a circuit for driving the light source  211 . The substrate  240  is attached to the outside of the side plate  201   d  on the side opposite to the fθ lens  231  of the housing  201  so that the emitting portion of the light source  211  and the light receiving portion of the beam detector  234  face to the inside of the housing  201 . The emitting portion of the light source  211  and the light receiving portion of the beam detector  234  face to the inside of the housing  201  through respective openings (not illustrated) formed in the side plate  201   d . As a result, the light source  211  can emit the light beam L from the emitting portion toward the collimator lens  212  in the housing  201 . The beam detector  234  can receive the light beam L from the beam detection lens  233  in the housing  201 , by using the light receiving portion. 
     Further, the deflection-scanning substrate  221  is a flat plate-shaped printed substrate that has a circuit for driving the deflection-scanning motor  222 . The deflection-scanning motor  222  is attached to the deflection-scanning substrate  221 , and the central portion of the deflection-scanning component  223  is connected and attached to the rotating shaft  222   a  of the deflection-scanning motor  222 . The deflection-scanning component  223  is rotationally driven by the deflection-scanning motor  222 . 
     Next, the optical path of light beam L from the light source  211  until entering the photoreceptor drum  3  will be described. 
     The light beam L of the light source  211  is transmitted through the collimator lens  212 , thus becomes substantially parallel light, is narrowed by the aperture component  213 , is transmitted through the cylindrical lens  214 , becomes incident on and then reflected by the light source reflecting mirror  215 , and becomes incident on a reflective surface  223   a  of the deflection-scanning component  223 . The deflection-scanning component  223  is rotated at a constant angular velocity in a predetermined rotation direction R by the deflection-scanning motor  222 , reflects the light beam L sequentially on each reflective surface  223   a , and repeatedly deflects the light beam L in the main scanning direction X 1  at a constant angular velocity. The fθ lens  231  focuses the light beam L on the surface of the photoreceptor drum  3  so as to have a predetermined beam diameter in both the main scanning direction X 1  and the sub-scanning direction. Further, the fθ lens  231  converts the light beam L deflected in the main scanning direction X 1  by the deflection-scanning component  223  at a constant angular velocity, so it moves at a constant linear velocity on the photoreceptor drum  3 . As a result, the light beam L can repeatedly scan the surface of the photoreceptor drum  3  in the main scanning direction X 1 . 
     Further, the beam detector  234  causes the light beam L reflected by the beam-detection reflecting mirror  232 , to be incident immediately before the main scanning (writing) of the photoreceptor drum  3  is started. The beam detector  234  receives the light of the light beam L at the time immediately before the start of the main scanning of the surface of the photoreceptor drum  3  and outputs a BD signal indicating the time immediately before the start of the main scanning. The start time of the main scan of the photoreceptor drum  3 , on which the toner image in formed, is set according to the BD signal, and the writing by the light beam L according to the image data is started. Then, the two-dimensional surface (peripheral surface) of the photoreceptor drum  3 , which is rotationally driven and charged, is scanned by the light beam L, and each electrostatic latent image is formed on the surface of the photoreceptor drum  3 . 
     Also, the closer the incident angle of the light beam L incident on the first dustproof glass plate  235  is to a right angle, the more the light transmission improves accordingly. In this regard, since the light beam L is scanned in the main scanning direction X 1 , if the first dustproof glass plate  235  is provided along the longitudinal direction W of the fθ lens  231 , for example, the following inconveniences occur. That is, the light beam L (directed to the beam detector  234  from the deflection-scanning component  223  light beam L) outside of the scanning area α (see  FIGS. 8A and 9 ), which is from the scanning start position to the scanning end position of the light beam L based on the deflection-scanning component  223  in relation to the first dustproof glass plate  235 , is too far inclined with respect to the first dustproof glass plate  235 , and so the light transmission deteriorates. 
     In this respect, in the present embodiment, the first dustproof glass plate  235  is inclined so as to face the beam detector  234  with respect to the longitudinal direction W of the fθ lens  231 . In this way, not only is it possible to avoid deterioration of the light transmission of the light beam L at the scanning area α with respect to the first dustproof glass plate  235 , but it is also possible to avoid deterioration of light transmission of the light beam L from the deflection-scanning component  223  toward the beam detector  234  with respect to the first dustproof glass plate  235 . Further, the deflection-scanning substrate  221  is arranged in parallel to or substantially parallel to the first dustproof glass plate  235 . 
     About the Present Embodiments 
     The optical scanning device  200  according to the present embodiment detects, by using the beam detector  234 , the main scanning start time of the light beam L emitted from the light source  211  and deflection-scanned in the main scanning direction X 1  by the deflection-scanning component  223 . 
     Next, the first to third embodiments will be described below with reference to  FIGS. 8A to 12B . 
     First Embodiment 
     In the optical scanning device  200  according to the first embodiment, on the light source  211  and the beam detector  234 , the emission side (emitting portion) of the light source  211  and light receiving side (light receiving portion) of the beam detector  234  face the light-incident side of the fθ lens  231 , which is longest in the main scanning direction X 1  and causes incidence of a light beam L detection-scanned by the deflection-scanning component  223 . Further, in the examples shown in  FIGS. 8A and 8B , on the light source  211  and the beam detector  234 , the light source  211  is arranged on the upstream side and the beam detector  234  is arranged on the downstream side in the main scanning direction X 1 , in the longitudinal direction W of the fθ lens  231 . In the example shown in  FIG. 9 , on the light source  211  and the beam detector  234 , the beam detector  234  is arranged on the upstream side and the light source  211  is arranged on the downstream side in the main scanning direction X 1 , in the longitudinal direction W of the fθ lens  231 . In this way, wasted space (particularly the space between the light source  211  and the deflection-scanning component  223 ) can be reduced, and as a result, the housing  201  can be decreased in size. 
     The light source  211  and the beam detector  234  are disposed along the main scanning direction X 1 . In this way, the light source  211  and the beam detector  234  can be arranged in a row in the main scanning direction X 1 , and the size of the housing  201  can be decreased accordingly. 
     In the examples shown in  FIGS. 8A and 8B , the light beam L (L 1 ) incident on the deflection-scanning component  223  and the light beam L (L 2 ) incident on the beam detector  234  intersect (see  FIG. 8A ) when viewed from the direction of the rotational axis of the deflection-scanning component  223  (height direction H of the fθ lens  231 ). In this way, wasted space can be further reduced, and as a result, the housing  201  can be further decreased in size. 
     Second Embodiment 
     In the optical scanning device  200  according to the first embodiment, the beam detector  234  is arranged on the main scanning start side with respect to the light beam L. In this way, the beam detector  234  can reliably detect the main scanning start time of the light beam L. 
     Also, the beam detector  234  is arranged on the main scanning start side with respect to the light beam L, but the beam detector  234  may be arranged on the main scanning end side with respect to the light beam L. 
       FIGS. 10 and 11  are plan views respectively illustrating an example and another example of the positional relationship between the light source  211  and the beam detector  234  in the optical scanning device  200  according to the second embodiment. 
     In the example shown in  FIG. 10 , the beam detector  234  is arranged on the upstream side and the light source  211  is arranged on the downstream side in the main scanning direction X 1 , in the longitudinal direction W of the fθ lens  231 . In the example shown in  FIG. 11 , the light source  211  is arranged on the upstream side and the beam detector  234  is arranged on the downstream side in the main scanning direction X 1 , in the longitudinal direction W of the fθ lens  231 . In this way, wasted space (particularly the space between the light source  211  and the deflection-scanning component  223 ) can be reduced, and as a result, the housing  201  can be decreased in size. 
     The beam detector  234  is arranged on the main scanning end side with respect to the light beam L. In this way, although it is necessary to add a beam-detection reflecting mirror  232   a  on the main scanning start side with respect to the light beam L for causing the light beam L from the deflection-scanning component  223  to be incident on the beam detector  234 , the beam detector  234  can detect the main scan start time of the light beam L on the main scanning end side with respect to the light beam L. 
     In the example shown in  FIG. 10 , the light beam L (L 1 ) incident on the deflection-scanning component  223  and the light beam L (L 2 ) incident on the beam detector  234  intersect when viewed from the height direction H of the fθ lens  231 . In this way, wasted space can be further reduced, and as a result, the housing  201  can be further decreased in size. 
     Third Embodiment 
       FIGS. 12A and 12B  are a plan view and a front view, each illustrating an example of the positional relationship between the light source  211  and the beam detector  234  in the optical scanning device  200  according to the third embodiment. 
     In the example shown in  FIGS. 12A and 12B , the light source  211  and the beam detector  234  are arranged at the same position in the longitudinal direction W of the fθ lens  231  (so that the optical axes are aligned in the height direction H). In this way, the space for providing the light source  211  and the beam detector  234  in the longitudinal direction W of the fθ lens  231  can be reduced as much as possible, and as a result, the housing  201  can be further decreased in size. 
     The beam detector  234  is arranged on the main scanning start side with respect to the light beam L. In this way, the beam detector  234  can reliably detect the main scanning start time of the light beam L. Further, the light beam L (L 1 ) incident on the deflection-scanning component  223  and the light beam L (L 2 ) incident on the beam detector  234  intersect when viewed from the height direction H of the fθ lens  231 . It is noted that the beam detector  234  may also be arranged on the main scanning end side with respect to the light beam L. It is also possible that the light beam L (L 1 ) incident on the deflection-scanning component  223  and the light beam L (L 2 ) incident on the beam detector  234  may not intersect when viewed from the height direction H of the fθ lens  231 . 
     About the First to Third Embodiments 
     In the first to third embodiments, the light source reflecting mirror  215  is provided nearer than the fθ lens  231  is to a side of the deflection-scanning component  223  in the orthogonal direction E that is orthogonal to both the main scanning direction X 1  (longitudinal direction W of the fθ lens  231 ) and the direction of the rotational axis (height direction H) of the deflection-scanning component  223 . The light source reflecting mirror  215  reflects the light beam L emitted from the light source  211  toward the deflection-scanning component  223 . In this way, the light beam L from the light source  211  can be folded back to the side opposite to the fθ lens  231  by the light source reflecting mirror  215 , and the size of the housing  201  can be reduced accordingly. 
     In the first to third embodiments, the substrate  240  is a single substrate provided along the main scanning direction X 1  (longitudinal direction W of the fθ lens  231 ). The substrate  240  is provided with a light source  211  and a beam detector  234 . In this way, the light source  211  and the beam detector  234  can be integrated on a single substrate, and the size of the housing  201  can be decreased accordingly. 
     In the first to third embodiments, the light source  211  and the beam detector  234 , with the deflection-scanning component  223  in between, are provided on the side opposite to the fθ lens  231  on the wall surface side (the outer wall surface of the side plate  201   d  via the substrate  240 ) in the housing  201  of the optical scanning device  200 . In this way, the space in the housing  201  can be effectively used. 
     In the first to third embodiments, the beam-detection reflecting mirror  232  is provided nearer than the fθ lens  231  is to the deflection-scanning component  223  in the orthogonal direction E that is orthogonal to both the main scanning direction X 1  and the rotational axis direction (height direction H) of the deflection-scanning component  223 . The beam-detection reflecting mirror  232  reflects the light beam L from the deflection-scanning component  223  toward the beam detector  234 . In this way, the light beam L from the deflection-scanning component  223  can be folded back to the side opposite to the fθ lens  231  by the beam-detection reflecting mirror  232 , and the size of the housing  201  can be reduced accordingly. 
     In the first to third embodiments, the beam-detection reflecting mirror  232  is arranged nearer than the light source reflecting mirror  215  is to the side of the fθ lens  231  in the orthogonal direction E that is orthogonal to both the main scanning direction X 1  and the rotational axis direction (height direction H) of the deflection-scanning component  223 . In this way, the space between the light source reflecting mirror  215  and the fθ lens  231  can be effectively used. 
     In the first embodiment and the second embodiment, the cylindrical lens  214  is provided on the optical path of the light beam L between the light source  211  and the deflection-scanning component  223  (in this example, the light source reflecting mirror  215 ). The beam detection lens  233  is provided on the optical path of the light beam L between the deflection-scanning component  223  (in this example, the reflective beam detection mirror  232 ) and the beam detector  234 . The arrangement position of the cylindrical lens  214  and the arrangement position of the beam detection lens  233  overlap in the orthogonal direction E that is orthogonal to both the main scanning direction X 1  (longitudinal direction W of the fθ lens  231 ) and the direction of the rotational axis (height direction H) of the deflection-scanning component  223  when viewed from the height direction H of the fθ lens  231 . In this way, the cylindrical lens  214  and the beam detection lens  233  can be integrated into one place in the orthogonal direction E, and the size of the housing  201  can be reduced accordingly. 
     The present invention is not limited to the embodiments described above, and can be implemented in various other forms. Therefore, the embodiments are merely examples in all respects and should not be interpreted to limit the present invention. The range of the present invention is shown by the range of claims and is not bound by the text of the specification. Further, all modifications and changes belonging to the equivalent range of the claims are within the range of the present invention. 
     DESCRIPTION OF THE DRAWINGS 
     
         
         
           
               100  Image forming apparatus 
               200  Optical scanning device 
               201  Housing 
               201   a  Bottom plate 
               201   b  Side plate 
               201   d  Side plate 
               201   e  Side plate 
               201   f  Second window 
               202  Upper lid 
               203  Deflection-scanning chamber 
               203   a  Opening 
               203   b  First window 
               204  Lower lid 
               210  Incident optical system 
               211  Light source 
               212  collimator lens 
               213  Aperture component 
               214  Cylindrical lens 
               215  Light source reflecting mirror 
               220  Deflection-scanning unit 
               221  Deflection-scanning substrate 
               222  Deflection-scanning motor 
               222   a  Rotating shaft 
               223  Deflection-scanning component 
               223   a  Reflective surface 
               230  Emission optical system 
               231  fθ lens 
               232  Beam-detection reflecting mirror 
               232   a  Beam-detection reflecting mirror 
               233  Beam detection lens 
               234  Beam detector 
               235  First dustproof glass plate 
               236  Second dustproof glass plate 
               240  Substrate 
               3  Photoreceptor drum (scanning object) 
             E Orthogonal direction 
             H Height direction 
             L Light beam 
             R Rotation direction 
             W Longitudinal direction 
             X 1  main scanning direction 
             α scanning area