JP2019008034A - Optical scanner and image forming apparatus including the optical scanner - Google Patents

Abstract

To prevent, in a tandem optical scanner including a cylinder lens part that condenses light beams emitted from a plurality of light sources, an incident area of the light beams on a reflection surface of a polygon mirror from being inclined with respect to a mirror rotation direction when seen from a mirror normal direction.SOLUTION: A cylinder lens part 42 is formed of a plurality of lens parts 42a to 42d through which a plurality of light beams D1 to D4 respectively pass. The plurality of lens parts 42a to 42d are respectively configured such that curvature-fixed straight lines Sa to Sd in which the curvature of radius becomes the same on a lens surface are not parallel to each other, and have inclination angles θa to θd with respect to a lens center line So that passes through the middle position in a sub-scanning direction of the cylinder lens part 42 when seen from the optical axis direction.SELECTED DRAWING: Figure 9

Description

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

  Conventionally, a tandem type optical scanning device having a cylinder lens unit that condenses light beams emitted from a plurality of light sources corresponding to yellow, magenta, cyan, and black colors on the same reflecting surface of a polygon mirror. 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 cylinder 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. However, the incident region of the light beam incident on the mirror reflecting surface extends in parallel to the mirror rotation direction (direction orthogonal to the rotation axis of the polygon mirror). 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. If so, the incident area of the light beam incident on the mirror reflecting surface is inclined in the sub-scanning direction with respect to the mirror rotation direction. As a result, the optical path of the light beam reflected by the mirror reflecting surface is likely to vibrate due to the influence of the surface accuracy of the mirror reflecting surface.

  The present invention has been made in view of such points, and an object of the present invention is to provide a cylindrical lens unit that condenses light beams emitted from a plurality of light sources on the same reflecting surface of a polygon mirror. In the tandem type optical scanning device, the incidence area of each light beam on the reflecting surface of the polygon mirror is prevented from tilting in the sub-scanning direction with respect to the mirror rotation direction, and thus the occurrence of image defects such as jitter is suppressed. There is.

  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. A plurality of emitted light beams are each provided with a cylindrical lens portion that is incident obliquely at different incident angles on the same reflecting surface of the polygon mirror to collect the light.

  The cylinder lens unit includes a plurality of lens units through which each of the plurality of light beams passes, and at least one of the plurality of lens units has a constant curvature straight line having the same curvature radius on the lens surface. The tilt lens unit has a predetermined tilt angle with respect to a lens center line passing through the center position in the sub-scanning direction of the cylinder lens unit when viewed from the optical axis direction. The angle is the maximum amount of tilt in the sub-scanning direction with respect to the mirror rotation direction on the reflecting surface of the light beam that has passed through the tilted lens unit, compared to the case where the constant curvature line of the tilted lens unit is parallel to the lens center line Is set to be small.

  According to the present invention, it is possible to suppress the incidence area of each light beam on the reflection surface of the polygon mirror from being inclined in the sub-scanning direction with respect to the mirror rotation direction, and thus to suppress the occurrence of image defects such as jitter. it can.

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 according to the embodiment. FIG. 3 is a schematic diagram linearly showing an optical path from the light source unit of the optical scanning device to the polygon mirror in the embodiment. FIG. 4 is a schematic diagram illustrating a state in which the light beam emitted from the light source of the optical scanning device in the embodiment is reflected by the polygon mirror. FIG. 5 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. 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 an upstream end portion in a rotation direction on a reflection surface of a polygon mirror. FIG. 7 is a schematic view seen from the rotation center side of the polygon mirror, showing a simplified incident region of the light beam incident on the reflection surface of the polygon mirror in the conventional optical scanning device. FIG. 8 is a side view showing a cylinder lens portion of the optical scanning device in the embodiment. 9 is a view taken in the direction of the arrow IX in FIG. FIG. 10 is a view corresponding to FIG. 8 in a conventional optical scanning device. 11 is a view taken in the direction of the arrow XI in FIG. FIG. 12 is a schematic diagram schematically showing an optical path of a light beam that has passed through a cylinder lens portion in a conventional optical scanning device. FIG. 13 is a schematic diagram schematically showing an optical path of a light beam that has passed through a cylinder lens portion in a conventional optical scanning device. FIG. 14 is a schematic view seen from the rotation center side of the polygon mirror, showing the incident area of the light beam incident on the reflection surface of the polygon mirror in a simplified manner in the scanning device of the present embodiment. FIG. 15 is an explanatory diagram for explaining a method of setting the inclination angle of the constant curvature curve of the split lens unit according to another embodiment. FIG. 16 is a schematic view seen from the rotation center side of the polygon mirror, showing the incident area of the light beam incident on the reflection surface of the polygon mirror in a simplified manner in the optical scanning device of another embodiment.

  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.

  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 polygon mirror 44 reflects and scans the light beams D1 to D4 emitted from the light source unit 40 in the main scanning direction.

  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 cylinder lens portion 42 that condenses the light beams D1 to D4 that have passed through the aperture onto the reflection surface 44a of the polygon mirror 44.

  The cylinder lens portion 42 has a structure in which one cylinder lens is divided into four in the height direction (see FIG. 8). Each of the divided lens portions 42a to 42d (hereinafter referred to as first to fourth divided lens portions 42a to 42d) is provided in a light path of 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. 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.

  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 made into substantially parallel light beams by the collimator lenses 41a to 41d, and then enter the divided lens portions 42a to 42d of the cylinder 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. The incident angles of the light beams D1 to D4 with respect to the reflection surface 44a of the polygon mirror 44 are different from each other when viewed in the sub-scan section (see FIG. 3). By making the incident angles different in this way, the optical path separation of the four light beams D1 to D4 is facilitated. The width in the mirror rotation direction of each of the light beams D1 to D4 incident on the reflecting surface 44a of the polygon mirror 44 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.

  5 and 6 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. FIG. 5 shows a state in which each of the light beams D1 to D4 is incident on the downstream end portion of the reflecting surface 44a. FIG. 6 shows that the polygon mirror 44 rotates in the clockwise direction from the state of FIG. Is incident on the upstream end of the reflecting surface 44a. As shown in each figure, among the light beams D1 to D4, a light component L1 closer to the downstream side in the mirror rotation direction and a 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 cylinder 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. 7).

  FIG. 7 is a diagram schematically showing an incident region R of the light beam D1 emitted from the light source 40a with respect to the reflection 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. 5 and 6) is larger in the incident region r3 than in the incident region r1, the inclination angle α3 of the incident region r3 is larger than the inclination angle α1 of the incident region 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. The maximum tilt amount in the sub-scanning direction with respect to the mirror rotation direction in the incident region R is represented by W in the figure. When the maximum tilt amount W is large, the reflected light path of the light beam D1 reflected by the reflecting surface 44a of the polygon mirror 44 is likely to vibrate due to the influence of the surface accuracy of the reflecting surface 44a. As a result, there is a problem that image defects such as jitter occur in the printed image.

  On the other hand, in this embodiment, as shown in FIGS. 8 and 9, the cylinder lens part 42 is divided into four divided lens parts 42a to 42d through which the four light beams D1 to D4 pass. The straight lines Sa, Sb, Sc and Sd (hereinafter referred to as constant curvature straight lines) having a constant radius of curvature in each of the divided lens portions 42a to 42d are center lines So of the cylinder lens portion 42 (the center of the cylinder lens portion 42 in the sub-scanning direction). It is made to have inclination | tilt angle (theta) a-thetad with respect to the straight line extended along a position. The center line So is a straight line extending along the center position of the cylinder lens portion 42 in the sub-scanning direction and extending in a direction perpendicular to the rotation axis of the polygon mirror 44. In FIG. 8, a step is shown between the divided lens portions 42a to 42d, but this step is actually a minute step that cannot be visually confirmed.

  According to the above configuration, the tilt amount in the sub-scanning direction with respect to the mirror rotation direction of the light beams D1 to D4 on the reflection surface 44a of the polygon mirror 44 can be adjusted. That is, in the conventional cylinder lens unit 100, as shown in FIGS. 10 and 11, constant curvature straight lines Sa to Sd in regions where the light beams D1 to D4 pass are parallel to each other. Therefore, as schematically shown in the lower part of FIG. 12, the light beams D1 to D4 (only the light beam D1 is shown in the figure) are inclined at the reflection surface 44a of the polygon mirror 44. On the other hand, in this embodiment, the constant curvature straight lines Sa to Sd of the divided lens portions 42a to 42d have inclination angles θa to θd with respect to the center line So, so that the lower part of FIG. As shown specifically, the amount of inclination of the light beams D1 to D4 (only the light beam D1 is shown in the figure) on the reflecting surface 44a of the polygon mirror 44 can be reduced.

  Next, a method for setting the inclination angles θa to θd of the constant curvature straight lines Sa to Sd will be specifically described. The inclination angles θa to θd are the maximum inclination amounts of the incident regions R of the light beams D1 to D4 on the reflecting surface 44a with respect to the mirror rotation direction, compared to the case where the constant curvature straight lines Sa to Sd are parallel to the center line So. W is set to be small. FIG. 14 shows an incident region R of the light beam D1 on the reflecting surface 44a. According to this figure, it can be seen that the maximum inclination amount W is reduced as compared with the conventional example of FIG. More specifically, the tilt angles θa to θd are set so that the incident region r3 having the largest tilt amount in the conventional example is parallel to the mirror rotation direction (that is, the tilt angle α3 is 0). Yes.

  The inclination angles θa to θd set in this manner vary depending on the incident angles of the light beams D1 to D1 with respect to the reflection surface 44a when viewed in the sub-scanning section. That is, in the split lens portions 42a to 42d through which the light beams D1 to D4 having the same incident angle pass, the inclination angles θa to θd of the constant curvature straight lines Sa to Sd are the same. In the present embodiment, θa = θd, θb = θc, and θa> θb are satisfied.

  As described above, in the present embodiment, the maximum inclination amount W in the sub-scanning direction with respect to the mirror rotation direction of each of the light beams D1 to D4 on the reflection surface 44a of the polygon mirror 44 is reduced. Therefore, the optical paths of the light beams D1 to D4 reflected by the reflection surface 44a of the polygon mirror 44 are suppressed from vibrating due to the influence of the surface accuracy of the reflection surface 44a (the curvature and inclination of the reflection surface 44a). can do. Therefore, occurrence of image defects such as jitter in the printed image can be suppressed.

  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 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 an underfield optical system that easily generates jitter is employed, the constant curvature straight lines Sa to Sd of the divided lens portions 42a to 42d are the center line So of the cylinder lens portion 42 in the sub-scanning direction. In contrast, by having predetermined inclination angles θa to θd, it is possible to reliably suppress the occurrence of image defects such as jitter.

<< Other embodiments >>
In the above embodiment, the inclination angles θa to θd are set so that the incident region r3 is along the mirror rotation direction (that is, α3 = 0). In this case, however, the incident region r1 and the incident region r2 are set. It is also conceivable that the inclination angles α1 and α2 of the above increase. Therefore, as shown in FIG. 15, the inclination angle θa is set so that the total value σ of w1 + w2 + w3 is minimized when w1 to w3 are inclination amounts in the sub-scanning direction with respect to the mirror rotation direction of the respective incident regions r1 to r3. ˜θd may be set. FIG. 16 shows the incident region R of the light beams D1 to D3 when the tilt angles θa to θc are set by this method. In this example, as a result, it can be seen that the region r2 is parallel to the mirror rotation direction.

  In the above embodiment, the constant curvature straight lines Sa to Sd are inclined with respect to the center line So for all of the divided lens portions 42a to 42d. However, the present invention is not limited to this, and the divided lens portions 42a and 42d are not limited to this. Only the constant curvature straight lines Sa and Sd may be inclined with respect to the center line So, and the constant curvature straight lines Sb and Sc of the divided lens portions 42b and 42c may be parallel to the center line So.

  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-described embodiment, the cylinder lens unit 42 is formed of one cylinder lens by the divided lens units 42a to 42d, but is not limited thereto. That is, the cylinder lens unit 42 may be configured by one (four in the above embodiment) cylinder lens 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 R incident area Sa constant curvature straight line Sb constant curvature straight line Sc constant curvature straight line Sd constant curvature straight line So center line W maximum inclination amount w1 inclination amount w2 inclination amount w3 inclination amount θa Inclination angle θb Inclination angle θc Inclination angle θd Inclination angle 1 Image forming device 15 Optical scanning device 40 Light source unit 42 Cylinder lens unit 42a First split lens unit (inclined lens unit)
42b Second split lens part (tilt lens part)
42c Third split lens part (tilt lens part)
42d Fourth lens segment (tilt lens)
44 polygon mirror 44a reflective surface

Claims (4)

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 cylinder lens portion that is incident obliquely at different incident angles on the same reflecting surface of the polygon mirror and collects the light,
The cylinder lens unit includes a plurality of lens units through which each of the plurality of light beams passes.
At least one of the plurality of lens portions has a lens constant line having a constant curvature radius on the lens surface as a lens center line passing through a center position in the sub-scanning direction of the cylinder lens portion when viewed from the optical axis direction. In contrast, an inclined lens unit having a predetermined inclination angle,
The inclination angle of the constant curvature straight line of the inclined lens portion is larger than that in the case where the constant curvature straight line of the inclined lens portion is parallel to the lens center line on the reflection surface of the light beam that has passed through the inclined lens portion. An optical scanning device which is set so that the maximum tilt amount in the sub-scanning direction with respect to the mirror rotation direction is small. The optical scanning device according to claim 1,
The inclination angle of the constant curvature straight line of the inclined lens portion is the mirror at each of the upstream end portion, the central portion, and the downstream end portion of the reflecting surface in the mirror rotation direction of the light beam passing through the inclined lens portion. An optical scanning device that is set so that the total amount of tilt in the sub-scanning direction with respect to the rotation direction is summed and the sum is minimized. The optical scanning device according to claim 1 or 2,
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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