JP2018124347A - Optical scanner and image forming apparatus including optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent, in a tandem optical scanner including a cylindrical lens that collects light beams emitted from a plurality of light sources, incident areas of the light beams on a reflection surface of a polygon mirror from being inclined with respect to the direction of rotation of a mirror when seen from the direction of the normal of the mirror.SOLUTION: A cylindrical lens part 42 comprises a plurality of lens parts 42a to 42d through which a plurality of light beams D1 to D4 respectively pass. The plurality of lens part 42a to 42d are arranged such that, when seen from a sub scanning direction, the generatrix directions of the lens parts 42a to 42d are inclined, by predetermined angles, with respect to the direction orthogonal to the direction of light paths of the light beams D1 to D4. The predetermined angles are set respectively to the lens parts 42a to 42d such that the widths in the sub scanning direction of the light beams D1 to D4 on a reflection surface 44a become small compared with a case where the direction of the normal of the lens parts 42a to 42c match the direction orthogonal to the direction of the light paths of the light beams D1 to D4.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical scanning device and an image forming apparatus including the optical scanning device.

  Conventionally, tandem light that has a cylindrical lens portion that condenses light beams emitted from a plurality of light sources corresponding to each color (for example, yellow, magenta, cyan, and black) on the same reflecting surface of a polygon mirror. A scanning device is known (see, for example, Patent Document 1). The cylinder lens unit condenses a plurality of light beams emitted from the light source obliquely incident on the reflection surface of the polygon mirror at different incident angles when viewed in the sub-scan section. Thus, the plurality of light beams collected on the reflection surface are reflected and separated at different reflection angles.

JP 2003-295079 A

  In the optical scanning device shown in Patent Document 1, the optical path length from the cylindrical lens portion to the reflecting surface is determined by the upstream light component and the downstream light component in the mirror rotation direction of the light beam emitted from each light source. Will be different. Here, when the light beam is perpendicularly incident on the reflecting surface of the polygon mirror as seen in the sub-scan section, the optical path length differs between the upstream light component and the downstream light component in the mirror rotation direction. Even so, the incident area of the light beam incident on the mirror reflecting surface extends parallel to the mirror rotation direction. However, in the tandem type optical scanning device, each light beam is obliquely incident on the reflecting surface of the polygon mirror, so that the optical path length differs between the upstream light component and the downstream light component in the mirror rotation direction. In this case, the incident region of the light beam incident on the mirror reflecting surface is tilted so as to intersect the mirror rotation direction when viewed from the mirror normal direction. As a result, there is a problem that image defects such as jitter occur in the printed image.

  The present invention has been made in view of such a point, and an object thereof is to include a cylindrical lens unit that condenses light beams respectively emitted from a plurality of light sources onto the same reflecting surface of a polygon mirror. In the tandem type optical scanning device, the incident area of each light beam on the reflection surface of the polygon mirror is prevented from tilting with respect to the mirror rotation direction when viewed from the mirror normal direction, and as a result, image defects such as jitter occur. It is to suppress.

  An optical scanning device according to the present invention is provided between a polygon mirror, a light source unit that emits a plurality of light beams at intervals in the sub-scanning direction, and between the polygon mirror and the light source unit. Each of the emitted light beams includes a cylindrical lens unit that collects light by obliquely entering the same reflecting surface of the polygon mirror at different incident angles.

  The cylindrical lens unit includes a plurality of lens units through which each of the plurality of light beams passes. Each of the plurality of lens units has a generatrix direction of each lens unit as viewed from the sub-scanning direction. Are arranged so as to be inclined by a predetermined angle with respect to the orthogonal direction of the optical path direction, and the predetermined angle is determined when the respective bus directions of the plurality of lens portions coincide with the orthogonal direction of the optical path direction of each light beam. In comparison, each lens unit is set so that the width of each light beam on the reflecting surface in the sub-scanning direction becomes smaller.

  An image forming apparatus according to the present invention includes the optical scanning device.

  According to the present invention, in the tandem type optical scanning device in which the light beams respectively emitted from the plurality of light sources are condensed on the same reflecting surface of the polygon mirror by the cylindrical lens unit and deflected and scanned by the polygon mirror, the polygon mirror It is intended to suppress the incidence area of each light beam on the reflecting surface from being inclined with respect to the mirror rotation direction when viewed from the mirror normal direction, and thereby to suppress the occurrence of image defects such as jitter.

FIG. 1 is a schematic diagram illustrating an image forming apparatus including an optical scanning device according to an embodiment. FIG. 2 is a side view illustrating a schematic configuration of the optical scanning device. FIG. 3 is a schematic diagram linearly showing the optical path from the light source unit to the polygon mirror. FIG. 4 is a schematic diagram showing a state in which the light beam emitted from the light source of the optical scanning device is reflected by the polygon mirror. FIG. 5 is an enlarged plan view showing the cylindrical lens portion. FIG. 6 is a schematic diagram showing an optical path of a conventional optical scanning device, and shows a state in which a light beam is reflected at a downstream end portion in a rotation direction on a reflection surface of a polygon mirror. FIG. 7 is a schematic diagram showing an optical path of a conventional optical scanning device, and shows a state in which a light beam is reflected at an upstream end portion in a rotation direction on a reflection surface of a polygon mirror. FIG. 8 is a schematic diagram showing a simplified incident position of a light beam incident on a reflecting surface of a polygon mirror in a conventional optical scanning device. FIG. 9 is a view corresponding to FIG. 7 in the present embodiment. FIG. 10 is a view corresponding to FIG. 8 in the present embodiment. FIG. 11 is a view for explaining a method of setting the tilt angle of each divided lens unit in another embodiment, and corresponds to FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiment.

<Embodiment>
FIG. 1 shows an image forming apparatus 1 according to the embodiment. The image forming apparatus 1 is a tandem color printer, and includes an intermediate transfer belt 7, a primary transfer unit 8 and a secondary transfer unit 9, a fixing unit 11, an optical scanning device 15, and four image forming units. Units 16a to 16d and first to fourth paper transport units 21 to 24 are provided.

  A paper feed cassette 3 is disposed in the lower part of the main body 2 of the image forming apparatus 1. The paper feed cassette 3 stores and accommodates paper (not shown) such as cut paper before printing. The sheets are separated and sent one by one toward the upper right of the sheet feeding cassette 3 in FIG.

  The first paper transport unit 21 is provided on the side of the paper feed cassette 3. The first paper transport unit 21 is disposed along the right side surface of the main body 2. The first paper transport unit 21 receives the paper sent out from the paper feed cassette 3 and transports the paper along the right side surface of the main body 2 to the upper secondary transfer unit 9.

  A manual paper feed unit 5 is provided on the left side of the paper feed cassette 3. In the manual sheet feeder 5, paper of a size that is not in the paper cassette 3, thick paper, an OHP sheet, or the like is placed. A second paper transport unit 22 is provided on the right side of the manual paper feed unit 5. The second paper transport unit 22 extends substantially horizontally from the manual paper feed unit 5 to the first paper transport unit 21 and joins the first paper transport unit 21. Then, the second paper transport unit 22 receives the paper sent from the manual paper feed unit 5 and transports it to the first paper transport unit 21.

  The optical scanning device 15 is disposed above the second paper transport unit 22. Here, the image forming apparatus 1 receives image data transmitted from the outside. The image data is stored in a temporary storage unit (not shown) and then sent to the optical scanning device 15 as necessary. The optical scanning device 15 irradiates the image forming units 16a to 16d with laser light controlled based on the image data.

  The image forming units 16 a to 16 d are provided above the optical scanning device 15. Each of the image forming units 16a to 16d has photosensitive drums 10a to 10d, respectively. Chargers 20a to 20d, developing devices 30a to 30d, and cleaning devices 35a to 35d are provided for the respective photosensitive drums 10a to 10d. The cleaning devices 35a to 35d are provided for cleaning the peripheral surfaces of the photosensitive drums 10a to 10d.

  An endless intermediate transfer belt 7 is provided above each of the image forming units 16a to 16d. The intermediate transfer belt 7 is wound around a plurality of rollers and is rotationally driven by a driving device (not shown).

  As shown in FIG. 1, the four image forming units 16a to 16d are arranged in a line along the intermediate transfer belt 7, and respectively form yellow, magenta, cyan, or black toner images. That is, in each of the image forming units 16a to 16d, the optical scanning device 15 irradiates the peripheral surfaces of the photosensitive drums 10a to 10d with laser light to form an electrostatic latent image of the original image, and the developing devices 30a to 30d Each color toner image is formed by developing the electrostatic latent image.

  The primary transfer portions 8a to 8d are respectively disposed above the image forming units 16a to 16d. The primary transfer portions 8 a to 8 d include primary transfer rollers 80 a to 80 d that primarily transfer the toner images formed by the image forming units 16 a to 16 d to the surface of the intermediate transfer belt 7. A transfer bias is applied to the primary transfer rollers 80a to 80d from a transfer bias power source (not shown). The toner images of the image forming units 16a to 16d are transferred to the intermediate transfer belt 7 at a predetermined timing by a transfer bias applied to the primary transfer rollers 80a to 80d. Thus, a color toner image is formed on the surface of the intermediate transfer belt 7 by superposing four color toner images of yellow, magenta, cyan, and black.

  The secondary transfer unit 9 has a secondary transfer roller 18 disposed on the right side of the intermediate transfer belt 7. A transfer bias is applied to the secondary transfer roller 18 by a transfer bias power source. The secondary transfer roller 18 sandwiches the paper P with the intermediate transfer belt 7. Thus, the toner image on the intermediate transfer belt 7 is transferred onto the paper P by the transfer bias applied to the secondary transfer roller 18.

  The fixing unit 11 is provided above the secondary transfer unit 9. Between the secondary transfer unit 9 and the fixing unit 11, a third paper transport unit 23 that transports the paper P onto which the toner image has been secondarily transferred to the fixing unit 11 is formed.

  The fixing unit 11 includes a heating roller 111 and a pressure roller 112 that rotate. The fixing unit 11 sandwiches the paper P between the heating roller 111 and the pressure roller 112 so that the toner image transferred to the paper P is heated and pressed to be fixed on the paper P.

  A branch portion 27 is provided above the fixing portion 11. The sheet P discharged from the fixing unit 11 is discharged from the branching unit 27 to the sheet discharging unit 28 formed on the upper part of the image forming apparatus 1 when double-sided printing is not performed. The discharge port portion from which the paper P is discharged from the branch portion 27 toward the paper discharge portion 28 functions as a switchback portion 29. When performing duplex printing, the switchback unit 29 switches the transport direction of the paper P discharged from the fixing unit 11.

-Details of optical scanning device-
Next, the details of the optical scanning device 15 will be described with reference to FIGS. 2 is a side view showing the optical scanning device, and FIG. 3 is a schematic diagram linearly showing the incident optical system from the light source unit 40 of the optical scanning device 15 to the reflection surface 44a of the polygon mirror 44. 4 is a schematic diagram showing how the light beams D1 to D4 emitted from the light sources 40a to 40d of the optical scanning device 15 are reflected by the polygon mirror 44. FIG.

  The optical scanning device 15 has a housing 43 (see FIG. 2). A polygon mirror 44 and a light source unit 40 (see FIGS. 3 and 4) that emit light beams D1 to D4 toward the polygon mirror 44 are disposed in the housing 43. In the present embodiment, the polygon mirror 44 has a regular hexagonal shape having six reflecting surfaces 44a on the side surface. The polygon mirror 44 is rotated at a predetermined speed by a motor (not shown).

  The light source unit 40 includes light sources 40a to 40d corresponding to colors of yellow, magenta, cyan, and black. The four light sources 40a to 40d are arranged at intervals in the sub-scanning direction (the rotational axis direction of the polygon mirror 44 and the vertical direction in FIG. 3). Each light source 40a-40d emits light beams D1-D4, respectively.

  On the upstream side of the optical path from the polygon mirror 44, there are four collimator lenses 41a to 41d provided corresponding to the respective light sources 40a to 40d, and light beams D1 to D4 that have passed through the collimator lenses 41a to 41d have a predetermined optical path width. And a cylindrical lens unit 42 for condensing the light beams D1 to D4 that have passed through the aperture onto the reflection surface 44a of the polygon mirror 44 are disposed. A first imaging lens 45a, a plurality of second imaging lenses 45b (see FIG. 2), and a plurality of folding mirrors 46a to 46h are disposed on the downstream side of the optical path from the polygon mirror 44. Each of the imaging lenses 45a and 45b is constituted by, for example, an fθ lens.

  The cylindrical lens portion 42 has a structure in which one cylindrical lens is divided into four in the height direction (see FIG. 3). Each of the divided lens portions 42a to 42d is provided in the light path of the light beams D1 to D4 emitted from the light sources 40a to 40d, respectively. The incident side surfaces of the first to fourth divided lens portions 42a to 42d have a cylindrical surface shape, and the emission side surface has a flat surface shape.

  As shown in FIG. 5, the first to fourth divided lens portions 42 a to 42 d have optical paths of the light beams D <b> 1 to D <b> 4 in the respective busbar directions (directions having no light collecting ability) when viewed from the sub-scanning direction. Are arranged so as to be inclined by a predetermined angle θa to θd with respect to the orthogonal direction. In the present embodiment, the inclination angle θa of the first divided lens portion 42a and the inclination angle θd of the fourth divided lens portion 42d are equal, and the inclination angle θb of the second divided lens portion 42b and the inclination angle θc of the third divided lens portion 42c. Is equal to

  Next, the operation of the optical scanning device 15 will be described with reference to FIGS. The light beams D1 to D4 emitted from the light sources 40a to 40d are converted into substantially parallel light beams by the collimator lenses 41a to 41c, and then enter the divided lens portions 42a to 42d of the cylindrical lens portion 42. The light beams D1 to D4 incident on the divided lens portions 42a to 42d are emitted in the state of parallel light beams in the main scanning section (cross section perpendicular to the sub-scanning direction), and are sub-scanned (in the sub-scanning direction). (The cross section) converges and exits, and obliquely enters the reflecting surface 44a of the polygon mirror 44 to form an image. At this time, in order to facilitate the optical path separation of the four light beams D1 to D4 deflected by the polygon mirror 44, each of the light beams D1 to D4 is seen from the sub-scan section (see FIG. 3), and the reflecting surface 44a. Are incident at different angles. In the present embodiment, the width of each light beam D1 to D4 incident on the reflecting surface 44a of the polygon mirror 44 in the mirror rotating direction is narrower than the width of the reflecting surface 44a (see FIG. 4).

  The light beams D1 to D4 incident on the reflecting surface 44a of the polygon mirror 44 are scanned at a constant angular velocity by the polygon mirror 44, and then converted to a constant velocity scanning light by the first imaging lens 45a. The light beams D1 to D4 that have passed through the first imaging lens 45a are reflected by the folding mirrors 46a to 46g, respectively, and pass through the second imaging lens 45b to obtain the surfaces (scanned surfaces) of the photosensitive drums 10a to 10d. ) 10p to 10s.

  6 and 7 show how the light beams D1 to D4 emitted from the light sources 40a to 40d are incident on the reflection surface 44a of the polygon mirror 44 in the conventional optical scanning device. 6 and 7 show how the light beams D1 to D4 are incident on the downstream end of the reflecting surface 44a. FIG. 7 shows that the polygon mirror 44 is rotated clockwise from the state shown in FIG. A state in which the light beam D1 is incident on the upstream end of the reflecting surface 44a is shown. As shown in each figure, among the light beams D1 to D4, the light component L1 closer to the downstream side in the mirror rotation direction and the light component L2 closer to the upstream side in the rotation direction cause the polygon mirror 44 to move from the principal point of the cylindrical lens unit 100. A difference (hereinafter referred to as an optical path length difference δ) occurs in the distance to the reflecting surface 44a. Here, as shown in FIG. 3, each of the light beams D1 to D4 is inclined with respect to the normal direction of the reflecting surface 44a when viewed in the sub-scanning section, and thus there exists such an optical path length difference δ. Then, the incident region R of each of the light beams D1 to D4 incident on the reflecting surface 44a is inclined with respect to the mirror rotation direction when viewed from the mirror normal direction (see FIG. 8).

  FIG. 8 is a diagram schematically showing an incident region R of the light beam D1 emitted from the light source 40a with respect to the reflecting surface 44a in the conventional optical scanning device. In this figure, the incident region R is simply divided into three incident regions r1 to r3. The incident area r1 corresponds to the case where the light beam D1 is incident on the downstream end of the reflecting surface 44a in the mirror rotation direction as shown in FIG. 6, and the incident area r2 is the mirror rotation of the light beam D1 on the reflecting surface 44a. The incident region r3 corresponds to the case where the light beam D1 is incident on the upstream end of the reflecting surface 44a in the mirror rotation direction as shown in FIG. Since the optical path length difference δ (see FIGS. 6 and 7) is larger in the incident area r3 than in the incident area r1, the inclination angle α3 of the incident area r3 is larger than the inclination angle α1 of the incident area r1. In the incident region r2, the optical path length difference δ is smaller than the incident region r3 and larger than the incident region r1, and therefore the relationship α1 <α2 <α3 is satisfied. When the inclination angles α1 to α3 are large, the width (height) W in the sub-scanning direction of the light beam D1 incident on the reflection surface 44a of the polygon mirror 44 becomes large, and image defects such as jitter are likely to occur.

  On the other hand, in the present embodiment, the cylindrical lens unit 42 is divided into four divided lens units 42a to 42d through which the four light beams D1 to D4 pass, and the buses of the divided lens units 42a to 42d are configured. The direction is inclined by a predetermined angle θa to θd with respect to the orthogonal direction of the optical path of each of the light beams D1 to D4 when viewed from the sub-scanning direction. In this embodiment, the predetermined angles θa to θd are viewed from the sub-scanning direction on the assumption that the light beams D1 to D4 are incident on the downstream end in the rotation direction of the reflection surface 44a of the polygon mirror 44. Sometimes, the distance from the principal points at both ends of each of the divided lens portions 42a to 42d to the reflecting surface 44a is set to be substantially equal. In FIG. 9, as an example, a state in which the light beam D <b> 1 passing through the first divided lens portion 42 a is incident on the downstream end portion in the rotation direction of the reflection surface 44 a of the polygon mirror 44 is shown. Points S1 and S2 in the figure are principal points at both ends of the first divided lens portion 42a, and satisfy the relationship of distance K1 = distance K2. The method of setting the tilt angles θb to θd of the second to fourth split lens portions 42b to 42d is the same as the method of setting the tilt angle θa of the first split lens portion 42a described above. The inclination angles θa to θd are angles determined according to the incident angles of the light beams D1 to D1 when viewed in the sub-scanning section. In this embodiment, θa (= θd)> θb (= θc). Satisfies the relationship.

  In this way, each split lens is based on the state in which each light beam D1 to D4 is incident on the upstream end in the rotational direction of the reflecting surface 44a of the polygon mirror 44 (that is, the state corresponding to the incident region r3 in FIG. 8). Each light beam incident on the reflecting surface 44a is inclined by tilting the generatrix direction of each of the divided lens portions 42a to 42d so that the distances from the principal points at both ends of the portions 42a to 42d to the reflecting surface 44a of the polygon mirror 44 are equal. Of the incident areas r1 to r3 of D1 to D4, the incident area r3 having the largest inclination can be set along the mirror rotation direction (see FIG. 10). Thereby, the width W in the sub-scanning direction of each of the light beams D1 to D4 incident on the reflection surface 44a of the polygon mirror 44 can be reduced, and image defects such as jitter can be suppressed.

  Here, in the above embodiment, an underfield optical system is employed in which the width in the mirror rotation direction of each of the light beams D1 to D4 incident on the reflection surface 44a of the polygon mirror 44 is smaller than the width of the reflection surface 44a. When the underfield optical system is adopted, the output efficiency is increased because all of the light beams D1 to D4 emitted from the light source unit 40 are used for forming a latent image, compared with the case where the overfield optical system is adopted. Since the incident areas of the light beams D1 to D4 on the reflection surface 44a are narrow, the influence of the surface accuracy (curvature and inclination of the reflection surface) of the reflection surface 44a on the occurrence of image defects such as jitter increases. In the present invention, even when such an underfield optical system that easily generates jitter is employed, the generatrix direction of each of the divided lens portions 42a to 42d is inclined by a predetermined angle θa to θd with respect to the orthogonal direction of the optical path. The occurrence of image defects such as jitter can be reliably suppressed.

<< Other embodiments >>
In the above embodiment, the inclination angles θa to θd in the generatrix direction of the divided lens portions 42a to 42d are set so that the incident region r3 is along the mirror rotation direction (that is, α3 = 0). In this case, the inclination angles α1 and α2 of the incident region r1 and the incident region r2 may be conversely increased. Therefore, as shown in FIG. 11, when the widths of the incident areas r1 to r3 in the sub-scanning direction are set to w1 to w3, the direction of the buses of the divided lens portions 42a to 42d is set so that the total value σ of w1 + w2 + w3 is minimized. The inclination angles θa to θd may be set.

  The method for setting the predetermined angles θa to θd is not limited to the method described above. That is, the width W in the sub-scanning direction of each of the light beams D1 to D4 on the reflecting surface 44a is compared with the case where the generatrix direction of each of the divided lens portions 42a to 42d coincides with the orthogonal direction of the optical path direction of each of the light beams D1 to D4. Any setting method may be employed as long as the setting method is such that the value becomes small.

In the above embodiment, an underfield optical system is employed in which the width of the light beams D1 to D4 incident on the reflection surface 44a of the polygon mirror 44 in the mirror rotation direction is narrower than the width of the reflection surface 44a. The present invention is not limited to this, and an overfield optical system in which the width of the light beams D1 to D4 incident on the reflection surface 44a of the polygon mirror 44 in the mirror rotation direction is wider than the width of the reflection surface 44a may be adopted. Here, when the overfield optical system is employed, the entire area in the width direction of the reflecting surface 44a is used as the incident region of the light beams D1 to D4, so that an image such as jitter is obtained as compared with the case where the underfield optical system is employed. It is possible to reduce the influence of the surface accuracy (curvature or inclination of the reflecting surface) of the reflecting surface 44a on the occurrence of defects. Therefore, the occurrence of image defects such as jitter can be more reliably suppressed.
In the above embodiment, the cylindrical lens unit 42 includes one cylindrical lens constituted by the divided lens units 42a to 42d. However, the present invention is not limited to this. That is, the cylindrical lens unit 42 may be configured by one (four in the above embodiment) cylindrical lenses for each light source.

  As described above, the present invention is useful for an optical scanning device and an image forming apparatus including the optical scanning device.

σ Total value D1 Light beam D2 Light beam D3 Light beam D4 Light beam K1 Distance K2 Distance L1 Light component L2 Light component W Beam incident area width in the sub-scanning direction w1 Light beam incident area width in the sub-scanning direction
w2 Width of the light beam incident area in the sub-scanning direction w3 Width of the light beam incident area in the sub-scanning direction θa Predetermined angle θb Predetermined angle θc Predetermined angle θd Predetermined angle 1 Image forming device 15 Optical scanning device 40 Light source unit 42 Cylindrical lens unit 42a First split lens section (each lens section)
42b Second split lens section (each lens section)
42c Third split lens section (each lens section)
42d Fourth divided lens section (each lens section)
44 polygon mirror 44a reflective surface

Claims (6)

A polygon mirror, a light source unit that emits a plurality of light beams at intervals in the sub-scanning direction, and a plurality of light beams that are provided between the polygon mirror and the light source unit, respectively. In the optical scanning device comprising a cylindrical lens portion that is incident obliquely at different incident angles on the same reflecting surface of the polygon mirror and collects the light,
The cylindrical lens unit includes a plurality of lens units through which each of the plurality of light beams passes,
Each of the plurality of lens portions is disposed so that the generatrix direction of each lens portion is inclined by a predetermined angle with respect to a direction orthogonal to the optical path direction of each light beam, as viewed from the sub-scanning direction,
The predetermined angle is such that the width of each light beam in the sub-scanning direction on the reflecting surface is smaller than when the generatrix direction of each of the plurality of lens portions coincides with the orthogonal direction of the optical path direction of each light beam. As described above, the optical scanning device is set for each of the lens units. The optical scanning device according to claim 1,
The predetermined angle is determined from the principal points at both ends of each lens unit when viewed from the sub-scanning direction in a state where each light beam is incident on the upstream end of the reflecting surface in the mirror rotation direction. The optical scanning device is set for each of the lens units so that the distance to the lens becomes substantially equal. The optical scanning device according to claim 1,
For each of the light beams, the width in the sub-scanning direction of the light beam incident area at each of the upstream end portion, the central portion, and the downstream end portion in the mirror rotation direction on the reflecting surface is summed, and the sum value is The optical scanning device in which the predetermined angle is set for each of the lens units so as to be minimized. In the optical scanning device according to any one of claims 1 to 3,
The optical scanning device, wherein the predetermined angle, which is an inclination angle of each lens unit, is an angle determined according to the incident angle of each light beam to the reflecting surface. In the optical scanning device according to any one of claims 1 to 4,
An optical scanning device employing an underfield optical system in which the width of each light beam incident on the reflection surface of the polygon mirror in the mirror rotation direction is narrower than the width of the reflection surface in the mirror rotation direction. An image forming apparatus comprising the optical scanning device according to claim 1.

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