JP2005189435A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner and an image forming apparatus in which reflected light on a cover member of the inlet/outlet port of light of a polygon mirror is prevented from directing to a light source or a image plane due to the reflection or the scatter of the light hitting a lens on the light source side or an imaging lens on the image plane side, and the occurrence of failure is preliminarily avoided. <P>SOLUTION: The apparatus is so composed to be provided with: a polygon motor with which the light from the light source is made incident to the polygon mirror 3 and the scanning light is emitted via a cover member 6; and an optical system including a lens 21a which focuses the scanning light on the image plane, and so composed that at least one of the condition (1) concerning the light path of the reflected light at the cover member with respect to the incident side of the lens and the condition (2) concerning the emitting side of the lens is satisfied. The condition (1) is H<RL-in and -H>RH-in, and the condition (2) is -H<RL-out and H>RH-out, where H stands for the height of the lens measured from the lens optical axis, RL-in stands for the height of reflected light (lower light) measured from the lens optical axis on the lens incident side, RH-in stands for the height of reflected light (upper light) measured from the lens optical axis on the lens incident side, RL-out stands for the height of reflected light (lower light) measured from the lens optical axis on the lens emitting side, and RH-out stands for the height of reflected light (upper light) measured from the lens optical axis on the lens emitting side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical scanning device having a polygon motor and an image forming apparatus.

  The optical scanning device is a device in which a polygon mirror is rotated by a polygon motor to scan a laser beam with respect to an image plane, and is widely used in image forming apparatuses such as laser imagers and laser printers, image reading apparatuses, and the like. In Patent Document 1 below, as shown in FIG. 5A, in a polygon motor 100 in which a polygon mirror 130 accommodated in a cover 120 is rotated by a motor 140, a cover glass 170 is perpendicular to the optical axis Z direction. It is disclosed that the ghost caused by the reflected light from the optical system such as the imaging lens 180 reflected by the cover glass 170 toward the optical axis Z direction by being tilted from the optical axis Z is disclosed.

  However, as shown in FIG. 5B, when the reflected light from the tilted cover glass 170 hits the upper or lower surface of the imaging lens (fθ lens) 180 on the image plane 190 side, the reflected or scattered light is not reflected. It may reach the image plane and cause image defects. Or, when the cover glass 170 is a cover glass on the light source side, it may return to the light source (semiconductor laser), and the laser oscillation may become unstable.

  Further, when the cover glass 170 is shared by the light source side and the image plane side (single glass), the reflected light of the laser light from the light source on the cover glass 170 has a very large amount of reflected light, which hits the upper or lower surface of the lens. If reflected or scattered, a serious image defect will occur.

In addition, when the light reflected by the fθ lens 180 is re-reflected by the cover glass 170, the reflection direction of the re-reflected light by the cover glass 170 changes with the rotation of the polygon mirror 130. The image defects when reflected or scattered are widespread.
JP 09-185002 A

  In view of the above-described problems of the prior art, the present invention is such that the reflected light from the cover member at the light entrance / exit of the polygon motor strikes the lens on the light source side or the imaging lens on the image plane side, and the light is reflected or scattered to cause the light source or It is an object of the present invention to provide an optical scanning device and an image forming apparatus which are prevented from going to the image plane and preventing occurrence of defects.

To achieve the above object, a first optical scanning device according to the present invention rotatably accommodates a polygon mirror in a casing, light from a light source is incident on the polygon mirror, and the scanning light is transmitted to the casing. An optical scanning device comprising: a polygon motor configured to emit light through a translucent image plane side cover member provided on the optical system; and an optical system including a lens for imaging the scanning light on the image plane The light path of the reflected light in the image surface side cover member is configured to satisfy at least one of the following condition (1) relating to the incident side of the lens and the following condition (2) relating to the exit side of the lens. It is characterized by.
H <RL-in or -H> RH-in (1)
-H <RL-out and H> RH-out (2)

However, H: Lens height from the lens optical axis RL-in: Reflected light (lower ray) on the lens incident side of the lens RH-in: Reflected light (upward ray) on the lens incident side Ray height from the lens optical axis RL-out: Ray height from the lens optical axis on the lens exit side of reflected light (lower ray) RH-out: From the lens optical axis on the lens exit side of reflected light (upward ray) Ray height

  According to this optical scanning device, when the condition (1) is satisfied, the reflected light from the image surface side cover member passes outside the lens on the incident side of the lens of the optical system on the image surface side and satisfies the condition (2). Since the reflected light from the image surface side cover member is transmitted through the lens of the optical system on the image surface side, the reflected light from the image surface side cover member hits the lens on the image surface side, and the light is reflected or scattered, so that the image surface Never go to. For this reason, it is possible to prevent occurrence of problems in image formation and the like.

  The height of the lens, the thickness of the lens, the distance between the image plane side cover member and the lens, and the lens light of the image plane side cover member so as to satisfy the condition in the first optical scanning device It is preferable to set an inclination angle with respect to the axis.

A second optical scanning device according to the present invention includes a light source and a light-transmitting light source side cover member in which a polygon mirror is rotatably accommodated in a casing, and light from the light source is provided in the casing on the polygon mirror. A polygon motor configured so that the scanning light is emitted toward the image plane, and the light from the light source is placed between the light source and the light source side cover member. In the optical scanning device in which an optical system including a lens is arranged for coupling to the light source, the light path of the reflected light in the light source side cover member is the following condition (3) on the reflected light incident side of the lens and the lens Further, the present invention is characterized in that it is configured to satisfy at least one of the following conditions (4) regarding the reflected light emitting side.
H <RL-in or -H> RH-in (3)
-H <RL-out and H> RH-out (4)

However, H: Lens height from the lens optical axis RL-in: Reflected light (lower ray) on the lens incident side of the lens RH-in: Reflected light (upward ray) on the lens incident side Ray height from the lens optical axis RL-out: Ray height from the lens optical axis on the lens exit side of reflected light (lower ray) RH-out: From the lens optical axis on the lens exit side of reflected light (upward ray) Ray height

  According to this optical scanning device, when the condition (3) is satisfied, the reflected light from the light source side cover member passes outside the lens on the incident side of the lens of the light source side optical system, and when the condition (4) is satisfied, Since the reflected light from the light source side cover member is transmitted through the lens of the optical system on the light source side, the reflected light on the light source side cover member does not hit the lens on the light source side and is reflected or scattered to go to the light source. For this reason, when the light source is a semiconductor laser, laser oscillation does not become unstable, and it is possible to prevent occurrence of problems in image formation and the like.

  In the second optical scanning device, the height of the lens, the thickness of the lens, the distance between the light source side cover member and the lens, and the optical axis of the light source side cover member with respect to the lens optical axis so as to satisfy the conditions It is preferable to set an inclination angle.

  In the first or second optical scanning device, the optical system includes a plurality of lenses, and the nth (n = 1) of the plurality of lenses counted from the image surface side cover member or the light source side cover member. , 2, 3,...) Is made higher than the (n + 1) th lens height Hn + 1 (Hn> Hn + 1 or | −Hn |> | −Hn + 1 |), the reflected light becomes n. Even if it passes through the nth lens, it can pass outside the n + 1th lens.

  The optical system includes a plurality of lenses, and the reflected light from the image surface side cover member or the light source side cover member is nth (n = 1, 2, 3,...) Of the plurality of lenses. ) And the outside of the (n + 1) th lens. The height of the lens, the thickness of the lens, the distance between the light source side cover member and the lens, and the tilt angle of the light source side cover member with respect to the optical axis of the lens so as to satisfy such a condition, , The interval between the nth lens and the (n + 1) th lens is set.

  In each case described above, a light blocking member that cuts the reflected light is arranged between the nth lens and the n + 1th lens, so that even if there is an optical axis shift or the like in the n + 1th lens, the reflected light is reflected. Can be reliably prevented from being directed to the image plane side or the light source side.

  The optical system includes a plurality of lenses, and the reflected light from the image surface side cover member or the light source side cover member strikes the upper surface or the lower surface of the (n + 1) th lens among the plurality of lenses. The nth lens (n = 1, 2, 3,...) Is configured such that the reflected light is transmitted through the lens, and the nth lens and the (n + 1) th lens are arranged between the nth lens and the n + 1th lens. By arranging a light blocking member that cuts the reflected light, even if the reflected light hits the upper or lower surface of the (n + 1) th lens (the above formula (1) or (3) is not satisfied), the nth lens Since the reflected light is transmitted through the lens and a light shielding member for cutting the reflected light is arranged between the nth lens and the n + 1th lens, even if there is an optical axis shift or the like in the n + 1th lens, Ensure reflected light Possible so as not directed to the image plane side or the light source side.

  In the first optical scanning device, the image surface side cover member and the light source side cover member on which light from the light source is incident on the polygon motor are formed of a single common member, so that the number of parts in the polygon motor is increased. In addition, even if the amount of reflected light from the common cover member from the light source is large, the scattering or reflection can be prevented, so that it is possible to prevent image defects.

  In the second optical scanning device, the light source side cover member and the image surface side cover member from which the scanning light is emitted from the polygon mirror toward the image surface are formed of a single common member. The number of components can be reduced, and even if the amount of reflected light from the common cover member from the light source is large, re-reflection or scattering can be prevented, and image defects can be prevented beforehand.

  An image forming apparatus according to the present invention includes the first or second optical scanning device described above, and is configured to form an image on the image plane. Thereby, when an image is formed on the image plane, an image defect can be prevented in advance, so that the image quality can be maintained.

  According to the optical scanning device and the image forming apparatus of the present invention, the reflected light from the cover member at the light entrance / exit of the polygon motor strikes the lens on the light source side or the imaging lens on the image plane side, and the light is reflected or scattered to cause the light source or image to be reflected. It is possible to prevent the occurrence of troubles by not facing the surface.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a plan view schematically showing an optical scanning device according to the present embodiment. FIG. 2 is a partial side view showing the main part of FIG.

  As shown in FIG. 1, the optical scanning device 1 according to this embodiment includes a laser light source 11 including a laser diode that emits laser light, and the laser light from the laser light source 11 is incident through a first cover member 5. A polygon motor 10 that is incident on the polygon mirror 3 rotated about the rotation axis 4 by the motor 2 and the scanning light exits through the second cover member 6, and the light emitted through the second cover member 6 is image surface 22. An imaging optical system 21 including a plurality of lenses such as an fθ lens.

  Between the laser light source 11 and the first cover member 5 of the polygon motor 10, a collimator lens 12 is disposed on the light source side, and a cylindrical lens 13 is disposed on the first cover member 5 side. Is imaged on the polygon mirror 3 by the optical system of the lenses 12 and 13.

  The polygon motor 10 accommodates the motor 2 and the polygon mirror 3 in a housing 9, a first cover member 5 is disposed at the light entrance of the housing 9, and a second cover member 6 is disposed at the light exit of the housing 9. Is arranged.

  The 1st cover member 5 and the 2nd cover member 6 are comprised from translucent flat plates, such as glass, and the 2nd cover member 6 inclines with respect to the perpendicular of the lens optical axis a like FIG. They are arranged at an angle θ. Similarly, the first cover member 5 is also tilted with respect to the normal of the lens optical axis b.

  The optical scanning device 1 scans the laser light from the laser light source 11 with the polygon motor 10, and the scanning light forms an image on the image plane 22 via the imaging optical system 21. Main scanning is performed in the scanning direction c, for example, image formation is performed.

  Next, in the optical scanning device 1 of FIG. 1, the reflected light reflected from the surface of the first cover member 5 by the laser light from the laser light source 11 strikes the upper and lower surfaces of the collimator lens 12 and the cylindrical lens 13 and is reflected or scattered. Light directed toward the laser light source 11 or emitted through the second cover member 6 is reflected from the lens of the imaging optical system 21 and re-reflected by the second cover member 6, and the upper and lower surfaces of the lens of the imaging optical system 21. A measure for preventing the light from being reflected or scattered toward the image plane 22 will be described.

  As shown in FIG. 2, in the optical scanning device 1 of FIG. 1, the respective light beam paths of the reflected lights A and C in the second cover member 6 of FIG. The light beam path of the reflected light B is configured to pass through the lens 21a.

  That is, the lens height H, the lens thickness D, the distance S in the optical axis a direction between the second cover member 6 and the lens 21a, and the second cover so as to satisfy the following expressions (1) and (2). An inclination angle θ of the member 6 with respect to the lens optical axis a is set.

  With respect to the lens height H and the light beam height R, the upper side from the optical axis a in FIG. Further, as shown in FIG. 2, the upper ray and the lower ray of the reflected light are higher than the principal rays A1, B1, C1 of the reflected light A, B, C, and the upper rays A2, B2, C2, The minus side from the principal ray is defined as lower rays A3, B3, and C3.

H <RL-in or -H> RH-in (1)
-H <RL-out and H> RH-out (2)

Where H: lens height from the lens optical axis RL-in: reflected light (lower light rays A3, C3) from the lens optical axis on the lens incident side RH-in: reflected light (upper light rays A2, C2) ) Of the light beam from the lens optical axis on the lens entrance side RL-out: the light beam height RH-out of the reflected light (lower light beam B3) from the lens optical axis on the lens output side: the reflected light (upper light beam B2) Ray height from the lens optical axis on the lens exit side

  As shown in FIG. 2, the height H of the lens 21a satisfies H <RL-in in the above formula (1) with respect to the lower ray A3 of the reflected light A with respect to the incident side (in) of the lens 21a, and the reflected light C Similarly, -H> RH-in in the formula (1) is satisfied for the upper light ray C2.

  Regarding the reflected light B, the height H of the lens 21a is such that the upper ray B2 and the lower ray B3 are -H <RL-out and H> in the above formula (2) with respect to the lens exit side (out) of the lens 21a. Meets RH-out.

  According to the optical scanning device 1 of FIGS. 1 and 2, when the condition (1) is satisfied, the reflected lights A and C from the cover member 6 are on the lens upper surface 21b or lower surface on the incident side of the lens 21a of the imaging optical system 21. When the light passes through the outside of 21c and satisfies the condition (2), the reflected light B is transmitted through the lens 21a of the imaging optical system 21, so that the reflected light A, B, C in the cover member 6 is the upper surface 21b of the lens 21a. The light hits the lower surface 21c and is not reflected or scattered to travel toward the image plane 22. For this reason, it is possible to prevent occurrence of problems in image formation and the like.

  In addition, the reflection direction of the re-reflected light reflected by the lens 21a re-reflecting by the cover member 6 changes relatively greatly with the rotation of the polygon mirror 3 and hits the upper surface or the lower surface of the lens, and reflection or scattering occurs. Although image defects cover a wide area on the image plane 22, reflection or scattering of the reflected light on the upper surface of the lens can be prevented beforehand by configuring as shown in FIG.

  The second cover member 6 in FIG. 2 is the light source side first cover member 5 in FIG. 1, the lens 21a in FIG. 2 is the light source side lenses 12 and 13, and the optical axis a is the optical axis. In the same manner, by satisfying the above conditions (3) and (4), the light reflected from the first cover member 5 on the light source side is outside the lenses 12 and 13 on the incident side of the lens. Since the light passes or passes through the lenses 12 and 13, the reflected light from the light source side cover member 6 does not hit the lens on the light source side and the light is reflected or scattered so that it does not go to the laser light source 11. For this reason, laser oscillation does not become unstable in the laser light source 11 made of a semiconductor laser, and it is possible to prevent problems in image formation and the like.

  Next, the case where the imaging optical system 21 of FIG. 1 includes a plurality of lenses will be described with reference to FIG. FIG. 3 is a partial side view showing the main part when the imaging optical system of FIG. 1 includes a plurality of lenses.

  As shown in FIG. 3, the height Hn from the optical axis a of the nth (n = 1, 2, 3...) Lens 31 from the second cover member 6 on the image plane side is the (n + 1) th lens 32. Is set so as to satisfy Hn> Hn + 1 or | −Hn |> | −Hn + 1 | with respect to the height Hn + 1 from the optical axis a of the lens and satisfy the conditions (1) and (2). The length Hn, the lens thickness Dn, the distance Sn between the cover member 6 and the lens 31, the distance Sn + 1 between the lenses 31 and 32, and the inclination angle θ of the cover member 6 from the perpendicular to the optical axis a are set.

  That is, the light path of the reflected light E at the second cover member 6 on the image plane side is as shown in FIG. 3, and the reflected light E is transmitted through the nth lens 31 including the upper light beam E2 and below. The light beam E3 passes outside the (n + 1) th lens 32. As a result, the reflected light E consisting of the principal ray E1, the upper ray E2 on the + side from the principal ray, and the lower ray E3 on the minus side from the principal ray hits the upper and lower surfaces of the lenses 31 and 32 and is reflected or scattered. There is no way to face 22.

  In addition, as shown in FIG. 3, by arranging a light shielding member 30 that cuts the reflected light from the second cover member 6 between the nth lens 31 and the (n + 1) th lens 32, the (n + 1) th lens 32. Even if there is an optical axis shift or the like, the reflected light can be reliably prevented from being directed toward the image plane side.

  Further, the height of the (n + 1) th lens 32 in FIG. 3 is not lowered due to optical design, lens processing restrictions, etc., and as shown by the broken line in FIG. 3, the upper surface 32a (or the lower surface) of the (n + 1) th lens 32. Even when the reflected light hits, the light shielding member for cutting the reflected light is arranged between the nth lens 31 and the (n + 1) th lens 32 so that the reflected light is not directed to the image plane side reliably. Can be.

  The second cover member 6 in FIG. 3 is the light source side first cover member 5 in FIG. 1, the lens 31 in FIG. 3 is the cylindrical lens 13 in FIG. 1, and the lens 32 is in the collimator lens 12 in FIG. The optical axis a is replaced with the optical axis b, and the reflected light from the first cover member 5 on the light source side passes through the cylindrical lens 13 and passes outside the collimator lens 12 in the same manner as in FIG. The height of the lenses 12 and 13, the thickness of the lenses 12 and 13, the distance between the cover member 5 and the lens 13, the angle of the cover member 5 with respect to the perpendicular to the optical axis b, and the distance between the lenses 12 and 13 are set. With this configuration, the light reflected from the cover member 6 on the light source side does not hit the lenses 13 and 12 and the light is reflected or scattered and does not travel toward the laser light source 11. Further, in a system in which reflected light hits the upper surface or the lower surface of the collimator lens 12, a light shielding member for cutting the reflected light is disposed between the cylindrical lens 13 and the collimator lens 12 (similar to the light shielding member 30 in FIG. 3). Also good.

  As described above, according to the optical scanning device 1 of the present embodiment, the reflected light from the cover members 5 and 6 disposed to be inclined with respect to the optical axes b and a is reflected on the light source side lens (cylindrical lens 13 or the like) or It does not hit the upper and lower surfaces of the image side lens (fθ lens or the like) 21a, 31, 32, and does not go to the laser light source 11 or the image plane 22.

  The optical scanning device 1 in FIG. 1 is applied to an image forming apparatus such as a laser printer or a laser imager, a recording medium such as a film is disposed at the position of the image plane 22 in FIG. Is imaged on the image plane 22 by the imaging optical system 21, and the recording medium is sub-scanned in the direction perpendicular to the paper surface of FIG. 1 while being scanned in the main scanning direction c by the polygon motor 10, thereby forming an image on the recording medium. be able to. In such an image forming apparatus, the reflected light from the cover members 5 and 6 of the polygon motor 10 of the optical scanning apparatus 1 in FIG. It does not occur and a good image can be obtained.

  Next, a modification of the optical scanning device in FIG. 1 will be described with reference to FIG. FIG. 4 is a plan view schematically showing a modification of the optical scanning device of FIG.

  The housing 49 of the polygon motor 40 of the optical scanning device 1 ′ in FIG. 4 has a cover member 41 made of a translucent plate material such as glass, and the incidence of laser light from the laser light source 11 and scanning light from the polygon mirror 3. Are emitted through the same cover member 41. Therefore, the reflected light from the common cover member 41 hits the upper and lower surfaces of the lens and is reflected or scattered so as not to go to the image plane 22 side and to the laser light source 11 as described above with reference to FIGS. By taking the same measures as described above, even if the reflected light amount of the reflected light from the laser light source 11 on the common cover member 41 is large, re-reflection or scattering of the reflected light can be prevented. Can be prevented. Further, since the cover member on the light source side and the image plane side is shared by one cover member 41, the number of parts in the polygon motor can be reduced.

  As described above, the best mode for carrying out the present invention has been described. However, the present invention is not limited to these, and various modifications are possible within the scope of the technical idea of the present invention. For example, the configuration of the plurality of lenses in FIG. 3 may be three or more. For example, reflected light from the cover member passes through the nth lens and the n + 1th lens from the cover member, and the n + 2th lens. The effect similar to FIG. 3 can be acquired by comprising so that it may pass outside. In this case, a light shielding member similar to that in FIG. 3 may be disposed between the (n + 1) th lens and the (n + 2) th lens.

It is a top view which shows schematically the optical scanning device by this Embodiment. It is a partial side view which shows the principal part of FIG. It is a partial side view which shows the principal part in case the optical system of FIG. 1 contains a some lens. It is a top view which shows roughly the modification of the optical scanning device of FIG. It is the side view (a) of the conventional polygon mirror, and the top view (b) for demonstrating generation | occurrence | production of the scattered light by the reflected light in the cover member of the conventional polygon mirror.

Explanation of symbols

1, 1 'optical scanning device 3 polygon mirror 5 first cover member (light source side cover member)
6 Second cover member (image surface side cover member)
DESCRIPTION OF SYMBOLS 10,40 Polygon motor 11 Laser light source 12 Collimator lens 13 Cylindrical lens 21 Imaging optical system 21a Lens 21b Lens upper surface 21c Lens lower surface 22 Image surface 30 Light-shielding member 31 Lens (nth lens)
32 lenses (n + 1th lens)
32a Upper surface 41 Cover member θ Inclination angle of cover member relative to normal of optical axis of lens A, B, C, E Reflected light A1, B1, C1, E1 Main rays of reflected light A2, B2, C2, E2 Upper rays of reflected light A3, B3, C3, E3 Downward ray of reflected light D, Dn Lens thickness H, Hn Lens height R Ray height S, Sn interval a Lens optical axis on image plane side b Lens optical axis on light source side c Main scanning direction

Claims (11)

A polygon mirror is rotatably accommodated in a housing so that light from a light source enters the polygon mirror, and the scanning light is emitted through a translucent image surface side cover member provided in the housing. In an optical scanning device comprising a configured polygon motor and an optical system including a lens for forming an image of the scanning light on an image plane,
The light path of the reflected light in the image side cover member is configured to satisfy at least one of the following condition (1) relating to the incident side of the lens and the following condition (2) relating to the exit side of the lens. An optical scanning device.
H <RL-in or -H> RH-in (1)
-H <RL-out and H> RH-out (2)
However, H: Lens height from the lens optical axis RL-in: Reflected light (lower ray) on the lens incident side of the lens RH-in: Reflected light (upward ray) on the lens incident side Ray height from the lens optical axis RL-out: Ray height from the lens optical axis on the lens exit side of reflected light (lower ray) RH-out: From the lens optical axis on the lens exit side of reflected light (upward ray) Ray height The height of the lens, the thickness of the lens, the distance between the image plane side cover member and the lens, and the tilt angle of the image plane side cover member with respect to the lens optical axis are set so as to satisfy the condition. The optical scanning device according to claim 1. A polygon mirror is rotatably accommodated in a light source and a casing, and light from the light source enters the polygon mirror through a translucent light source side cover member provided in the casing, and the scanning light is imaged. A polygon motor configured to emit light toward a surface, and an optical system including a lens for coupling light from the light source to the polygon mirror between the light source and the light source side cover member. In the arranged optical scanning device,
The light path of the reflected light in the light source side cover member satisfies at least one of the following condition (3) regarding the reflected light incident side of the lens and the following condition (4) regarding the reflected light emitting side of the lens. An optical scanning device characterized by comprising.
H <RL-in or -H> RH-in (3)
-H <RL-out and H> RH-out (4)
However, H: Lens height from the lens optical axis RL-in: Reflected light (lower ray) on the lens incident side of the lens RH-in: Reflected light (upward ray) on the lens incident side Ray height from the lens optical axis RL-out: Ray height from the lens optical axis on the lens exit side of reflected light (lower ray) RH-out: From the lens optical axis on the lens exit side of reflected light (upward ray) Ray height The height of the lens, the thickness of the lens, the distance between the light source side cover member and the lens, and the inclination angle of the light source side cover member with respect to the optical axis of the lens are set so as to satisfy the condition. The optical scanning device according to claim 3. The optical system includes a plurality of lenses, and the n-th lens height of the plurality of lenses is higher than the (n + 1) -th lens height counted from the image plane side cover member or the light source side cover member. The optical scanning device according to claim 1, wherein: (Hn> Hn + 1 or | −Hn |> | −Hn + 1 |) The optical system is composed of a plurality of lenses, and reflected light from the image plane side cover member or the light source side cover member is transmitted through the nth lens among the plurality of lenses, and passes outside the n + 1th lens. The optical scanning device according to claim 1, wherein the optical scanning device is configured to pass. 7. The optical scanning device according to claim 5, wherein a light blocking member for cutting the reflected light is disposed between the nth lens and the (n + 1) th lens. The optical system is composed of a plurality of lenses, and the reflected light from the image surface side cover member or the light source side cover member strikes the upper surface or the lower surface of the (n + 1) th lens among the plurality of lenses. The second lens is configured such that the reflected light is transmitted through the lens, and a light blocking member for cutting the reflected light is disposed between the nth lens and the n + 1th lens. The optical scanning device according to claim 1. 3. The optical scanning device according to claim 1, wherein the image plane side cover member and the light source side cover member on which light from the light source is incident on the polygon motor are formed of one common member. 5. The optical scanning device according to claim 3, wherein the light source side cover member and the image plane side cover member from which scanning light is emitted from the polygon mirror toward the image plane are formed of one common member. . An image forming apparatus comprising the optical scanning device according to claim 1 and forming an image on the image plane.

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