JP2002107646A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the size of a beam spot uniform on a surface to be scanned while securing a constant velocity in a main scanning direction by appropriately defining the shape of the lens surface on the optical deflecting means side of a 2nd image forming optical system constituted of two lenses, as for an optical scanner where the 2nd image forming optical system is arranged between the optical deflecting means and the surface to be scanned. SOLUTION: As for the lens L2 arranged on the surface 7 side to be scanned of the 2nd image forming optical system 6, the surface on the optical deflecting/reflecting surface 4 side is formed so that the cross section in the main scanning direction may be formed to a non circular arc shape, and so that the cross section in the subscanning direction may be formed to a convex shape, the surface on the surface 4 side is a toric surface with a rotary axis which is orthogonal to the optical axis and the main scanning direction, and the surface on the surface 7 side to be scanned is formed so that the cross section in the main scanning direction may be formed to a non circular arc shape with a nearly straight or concave shape near the optical axis and the cross section in the subscanning direction may be formed to a nearly straight or convex shape, and provided with a rotary axis (including a rotating radius ∞) which is orthogonal to the optical axis, and also, parallel to the main scanning direction. Besides, as the whole 2nd lens L2, the cross section in the main scanning direction has a small negative refractive power near the optical axis, and the cross section in the subscanning direction has a positive refractive power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and more particularly to an optical scanning device, in which a light beam emitted from a light source is reflected and deflected by a light deflecting device, and then optically scanned on a surface to be scanned via a scanning optical device having fθ characteristics. The present invention relates to an optical scanning device suitably used for a laser beam printer, a digital copying machine, a laser plate making device, and the like having an electrophotographic process in which image information is recorded.

[0002]

2. Description of the Related Art Conventionally, laser beam printers, digital copiers, laser plate making devices, and the like, which scan a light beam such as a laser beam on a surface to be scanned such as a photosensitive material and form an image on the surface to be scanned. Optical scanning devices are known. Such an optical scanning device includes a light deflecting unit such as a rotary polygon mirror that reflects and deflects a light beam emitted from a light source to scan the surface to be scanned, and an imaging optical system that forms the light beam on the surface to be scanned. And

As such an optical scanning device, the applicant of the present invention has disclosed in Japanese Patent Application No. 11-33821, in which a toric and aspherical lens are disposed on the light deflecting / reflecting surface side, and only a section in the sub scanning direction is positive. There has been proposed an optical scanning device in which a cylindrical lens having a refractive power is provided and which can correct the field curvature of component light mainly in the sub-scanning direction.

Further, as described in Japanese Patent Application Laid-Open No. 61-120112, a convex surface in which the absolute value of the radius of curvature increases in the section in the sub-scanning direction as the distance from the vicinity of the optical axis in the main scanning direction increases, or As described in Japanese Unexamined Patent Publication No. 3-33712, a lens using a concave surface whose absolute value of the radius of curvature becomes smaller from the vicinity of the optical axis in the main scanning direction in the sub-scanning direction section is arranged near the surface to be scanned. By decreasing the positive refractive power of the section in the sub-scanning direction or increasing the negative refractive power as the distance from the optical axis in the main scanning direction increases, the image of the component in the sub-scanning direction mainly becomes smaller. An optical system in which the surface curvature has been corrected has been proposed.

[0005]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application No. Hei.
In the optical scanning device disclosed in the specification of No. 33821,
Although the distortion associated with the curvature of field and the uniformity of the beam spot on the surface to be scanned is well corrected, the uniformity of the beam spot size on the surface to be scanned corresponding to any scanning angle in the effective scanning area is further improved. It is hoped that this will be achieved.

The present invention has been made in view of such circumstances, and provides an optical scanning device capable of achieving a uniform beam spot size on a surface to be scanned while ensuring constant speed in a main scanning direction. The purpose is to do so.

[0007]

An optical scanning device according to the present invention comprises a collimator lens for emitting a light beam from a light source as a substantially parallel light beam, and a first image forming the light beam in a sub-scanning direction at a predetermined position. An image forming optical system, a light deflecting means having a light deflecting / reflecting surface disposed at or near the predetermined position, and a second means for forming an image of a light beam reflected and deflected by the light deflecting means on a surface to be scanned. In the optical scanning device having an imaging optical system, the second imaging optical system includes two lenses, and one of the lenses disposed on the surface to be scanned has an auxiliary lens. A toric surface having a convex cross section in the scanning direction and a rotation axis orthogonal to the optical axis and the main scanning direction, and the other surface is a non-circular shape in which the cross section in the main scanning direction is substantially straight or concave near the optical axis. , The cross section in the sub-scanning direction is almost straight or convex A lens having a rotation axis orthogonal to the optical axis and parallel to the main scanning direction (including the rotation radius ∞), and the cross section in the main scanning direction is weak near the optical axis as a whole of the lens, and the cross section in the sub scanning direction is weak. It has a positive refractive power.

In the second imaging optical system, the lens disposed on the surface to be scanned has a surface on the light deflecting means side having a convex cross section in the main scanning direction and a convex cross section in the sub scanning direction. In the toric surface having a rotation axis orthogonal to the optical axis and the main scanning direction, the surface on the surface to be scanned, the cross section in the main scanning direction is away from the optical axis in a concave shape on the surface to be scanned near the optical axis. Accordingly, the non-arc shape having a convex shape on the surface to be scanned has a shape in which the cross section in the sub-scanning direction has an extremely large radius of curvature, and the cross section in the main scanning direction is weak near the optical axis as a whole of the lens. It is possible that the cross section has a positive refractive power.

In the second imaging optical system, the lens arranged on the surface to be scanned has a surface on the side of the light deflecting means whose section in the main scanning direction is substantially straight near the optical axis, Is a deformed cylindrical surface having a rotation axis orthogonal to the optical axis and parallel to the main scanning direction, such that the non-arc shape approaches the scanning surface side as it moves away from the scanning surface, and the cross section in the sub-scanning direction forms a convex shape. The surface on the scanning surface side is a toric surface having a concave section in the main scanning direction, a convex section in the sub-scanning direction, and having a rotation axis orthogonal to the optical axis and the main scanning direction. It is possible that the cross section in the main scanning direction has a weak negative power and the cross section in the sub scanning direction has a positive refractive power.

In each of the optical devices described above, the lens of the second imaging optical system which is provided on the light deflecting means side has a surface on the light deflecting means side having an arc-shaped or non-circular cross section in the main scanning direction. The circular arc-shaped curve is rotated by a rotation axis orthogonal to the optical axis and parallel to the main scanning direction, and the surface on the scanned surface side has a rotation axis orthogonal to the optical axis and the main scanning direction. It is preferable that the surface of the lens has a positive refractive power in both the main scanning direction cross section and the sub scanning direction cross section, and that the surface on the scanning surface side has a convex meniscus shape near the optical axis.

Further, each lens constituting the second image forming optical system is preferably made of a plastic material. Here, the “main scanning direction” means a direction parallel to the trajectory of the deflected light beam on the surface to be scanned, and the “sub scanning direction” is substantially orthogonal to the main scanning direction on the surface to be scanned. Means direction. Further, the “section in the main scanning direction” means a section in the main scanning direction including the optical axis, and the “section in the sub-scanning direction” means a section perpendicular to the section in the main scanning direction and including the optical axis.

"Non-circular arc" means a line shape that is not a circular arc in a predetermined cross section. Further, the “aspheric surface” described later means a rotationally symmetric surface shape obtained by rotating a non-circular arc with the optical axis as a rotation axis.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating a configuration of an optical scanning device according to an embodiment of the present invention.

As shown in FIG. 1, the optical scanning device according to the present invention includes a collimator lens 2 for emitting a light beam from a light source 1 as a substantially parallel light beam, and a sub-scanning of the substantially parallel light beam at or near a predetermined position. A cylindrical lens 3 serving as a first image forming optical system for forming an image in a direction, and a plurality of light deflecting / reflecting surfaces 4 near the predetermined position. A polygon mirror 5 serving as a light deflecting means for scanning on the surface 7 and a light beam reflected and deflected by the polygon mirror 5 are imaged on the surface 7 to be scanned, and the light beam is scanned on the surface 7 at a substantially constant speed. And a second imaging optical system 6 acting as described above. In addition,
A scanning line 8 is shown on the scanned surface 7.

The second imaging optical system 6 includes a first lens L ₁ on the light deflection / reflection surface 4 side and a second lens L ₁ on the surface 7 to be scanned.
₂ consisting of two lenses.

Next, referring to FIG. 2, a second imaging optical system 6 will be described.
Will be described. FIG. 2 shows a plan view (a) and a longitudinal sectional view (b) of the second imaging optical system 6 of the optical scanning device according to the embodiment of the present invention.

[0017] The first lens L _1, the surface of the light deflection reflecting surface 4 side, rotating in the main scanning cross section is a curve of the non-arcuate shape, perpendicular to the optical axis, and a rotational axis parallel to the main scanning direction The surface on the scanning surface 7 side is a toric surface having an optical axis and a rotation axis orthogonal to the main scanning direction. Also,
As the first lens L ₁ overall, the main scanning cross section and has a both positive refractive power in the sub scanning cross section, the plane of the scan surface 7 side without a meniscus shape convex in the vicinity of the optical axis. The surface on the side of the light deflecting / reflecting surface 4 may be formed in an arc shape in a cross section in the main scanning direction.

[0018] The second lens L _2, the surface of the light deflection reflecting surface 4 side, the main non-arc shape in the scanning direction cross section, the sub-scanning cross section with the convex shape, the rotation axis perpendicular to the optical axis and the main scanning direction The surface on the side to be scanned 7 has a non-arc shape whose cross section in the main scanning direction is substantially straight or concave near the optical axis, and has a substantially straight or convex shape in the sub scanning direction. And has a rotation axis (including a rotation radius ∞) parallel to the main scanning direction. Also, the second
Lens L ₂ as a whole the negative main scanning cross section in the vicinity of the optical axis is weak, the sub-scanning cross section has a positive refractive power.

Further, the second lens L ₂ is a surface of the light deflection reflecting surface 4 side, both the main scanning cross section and the sub-scanning cross section is such as to form a convex shape, orthogonal to the optical axis and the main scanning direction Scanning surface 7 having a rotating axis
The surface on the side has a non-arc shape in which the cross section in the main scanning direction is near the optical axis and concave toward the surface to be scanned and convex toward the surface to be scanned 7 as the distance from the optical axis increases, and the cross section in the sub scanning direction has an extremely large curvature. It is possible to have a shape having a radius. Also,
The surface on the side of the light deflecting / reflecting surface 4 is formed such that the cross section in the main scanning direction is substantially straight near the optical axis, and the non-circular shape approaches the scanned surface 7 as the distance from the optical axis increases, and the cross section in the sub scanning direction is convex. A deformed cylindrical surface having a rotation axis perpendicular to the optical axis and parallel to the main scanning direction, and the surface on the side to be scanned has a concave shape in the main scanning direction and a convex shape in the sub-scanning direction. It is also possible to use a toric surface having an axis and a rotation axis orthogonal to the main scanning direction.

Further, the surface shape on the light deflection / reflection surface 4 side and the surface shape on the scanned surface 7 side may be exchanged. Further, it is preferable that the first lens L ₁ and the second lens L ₂ constituting the second imaging optical system 6 are made of a plastic material. By configuring the second imaging optical system 6 with lenses made of a plastic material in this way, the workability of each lens is improved, and the manufacturing is facilitated.
Cost can be reduced.

Hereinafter, in the optical system of the optical scanning device according to the present invention, an embodiment of the second imaging optical system 6, which is a feature thereof, will be described using specific numerical values. In addition,
Numerical data in the following embodiments are standardized by the focal length in the main scanning direction.

<Embodiment 1> The second imaging optical system 6 in Embodiment 1 is composed of two lenses L ₁ and L ₂ and has the configuration shown in FIG. 2 described above.

The second imaging optical system 6 in the first embodiment
Radius of curvature R _H , R _V ( _RH is the radius of curvature in the cross section in the main scanning direction, R _V is the radius of curvature in the cross section in the sub scanning direction, and the same applies to the following Examples 2 and 3. ), Lens spacing (or lens thickness) of each lens
D, and the refractive index N of each lens at a wavelength of 780 nm.
Are shown in the upper row of Table 1. However, in Table 1 and Tables 2 and 3 to be described later, the numbers corresponding to the symbols R, D, and N are sequentially increased from the light deflection reflection surface 4 side. The curvature radius R _H, R _V, as described below, the lens surface is the case of the non-arcuate become surface or aspherical in the main scanning direction cross section shows the numerical values of the curvature radius near the optical axis.

[0024]

[Table 1]

Here, each lens surface will be described. In each lens surface, the non-arc shape of the surface whose shape in the predetermined cross section is a non-arc is expressed by the following non-arc / aspheric formula. This non-circular arc / aspherical surface expression is the same in the non-circular arc shape and the aspherical surface shape in Examples 2 and 3 below.

[0026]

(Equation 1)

In the middle part of Table 1 above, each coefficient 1 / of each non-circular arc shown in the above-mentioned non-circular arc / aspherical formula in the first embodiment is shown.
The values of R, K, A ₄ , A ₆ , A ₈ , and A ₁₀ are shown. The first surface, that is, the first surface disposed on the light deflecting / reflecting surface 4 side
Surface of the light deflection reflecting surface 4 side of the lens L _1, said non-arc / the non-arc in the main scanning cross section, represented by the aspherical equation and coefficients, the optical axis from the point of the non-arcuate intersects the optical axis It has a shape formed by rotating a straight line parallel to the optical axis and parallel to the main scanning direction as a rotation axis on the same cross section including a point separated by the radius of curvature R _V1 above.

The second surface, i.e., the plane of the scan surface 7 side of the first lens L ₁ disposed on the light deflecting reflection face 4 side, a circular arc comprising a radius of curvature R _V2, the arc intersects the optical axis a shape formed by a straight line perpendicular to the main scanning cross section including a point at a distance radius of curvature R _H2 on the optical axis from the point is rotated as a rotation axis.

The third surface, i.e., the surface of the light deflection reflecting surface 4 side of the second lens L ₂ disposed on the scan surface 7 side, a circular arc comprising a radius of curvature R _V3, the arc intersects the optical axis a shape formed by a straight line perpendicular to the main scanning cross section including a point at a distance radius of curvature R _H3 on the optical axis from the point is rotated as a rotation axis.

The fourth surface, i.e., the plane of the scan surface 7 side of the second lens L ₂ disposed on the scan surface 7 side in the main scanning represented by the non-arc / aspheric expression and coefficients The non-circular arc on the cross section includes a point on the optical axis away from the point where the non-circular crosses the optical axis by a radius of curvature R _V4, and is orthogonal to the optical axis in the cross section and parallel to the main scanning direction. It forms a shape formed by rotating a straight line as a rotation axis.

In the lower part of Table 1, the distance D ₀ from the light deflecting / reflecting surface 4 to the first surface, the focal length f _{H in the} main scanning direction, the focal length f _V in the sub scanning direction, and the light The values of the magnification β _V , the half angle of view θ, and the focal length f _{2H in} the main scanning direction near the optical axis of the second lens L ₂ are shown in the section in the sub-scanning direction between the deflecting reflecting surface 4 and the surface 7 to be scanned. .

<Embodiment 2> The second image forming optical system 6 in Embodiment 2 is composed of two lenses, and the above-described Embodiment 1
Compared to the surface of the scan surface 7 side, instead of being a non-arc shape in which the surface of the light deflection reflecting surface 4 side in the second lens L ₂ of the surface shape becomes linear in the vicinity of the optical axis in the main scanning cross section Are arc-shaped in the cross section in the main scanning direction.

Second imaging optical system 6 in the second embodiment
Of each lens surface, R _H , R _V , lens spacing (or lens thickness) D of each lens, and wavelength 7 of each lens
The upper row of Table 2 shows the refractive index N at 80 nm.

[0034]

[Table 2]

In the middle part of Table 2 above, each coefficient 1 / R, K, A ₄ , A ₆ , A ₈ , A _{10 of} each non-circular arc shown in the non-circular arc / aspherical surface equation in the second embodiment. Indicates the value of
In the lower part of Table 2, the surface distance D ₀ from the light deflecting / reflecting surface 4 to the first surface in the second embodiment, the focal length f _H in the main scanning direction,
The focal length f _V in the sub-scanning direction, the magnification β _{V of} the cross section in the sub-scanning direction between the light deflection reflecting surface 4 and the surface 7 to be scanned, the half angle of view θ, the second
Shows the values of the focal length f _2H in the main scanning direction in the vicinity of the optical axis of the lens L _2.

<Embodiment 3> The second image forming optical system 6 in Embodiment 3 is composed of two lenses.
The configuration is almost the same as that described above. The radius of curvature _RH of each lens surface of the second imaging optical system 6 in the third embodiment,
R _V , the lens interval (or lens thickness) D of each lens,
Table 3 shows the refractive index N of each lens at a wavelength of 780 nm.

[0037]

[Table 3]

In the middle part of Table 3 above, each coefficient 1 / R, K, A ₄ , A ₆ , A ₈ , A _{10 of} each non-circular arc shown in the above-mentioned non-circular arc / aspheric surface equation in the third embodiment. Indicates the value of
The lower part of Table 3 shows the light deflection / reflection surface 4 in the third embodiment.
From the first surface to the first surface D ₀ , the focal length f in the main scanning direction
_H , the focal length f _V in the sub-scanning direction, the magnification β _{V of} the cross section in the sub-scanning direction between the light deflection reflecting surface 4 and the surface to be scanned 7, the half angle of view θ,
The focal length f of the main scanning direction in the vicinity of the optical axis of the second lens L ₂
Each value of _2H is shown.

FIGS. 3 to 5 show aberration diagrams (field curvature and distortion) of the optical system of the optical scanning apparatus according to the first to third embodiments. In each aberration diagram of the field curvature, aberrations in the main scanning direction and the sub scanning direction are shown. FIG.
As is clear from FIGS. 5 to 5, according to each of Examples 1 to 3, each aberration is satisfactorily corrected.

In the above-described embodiment, a lens using a concave surface whose absolute value of the radius of curvature increases in the main scanning direction from the vicinity of the optical axis in the cross section in the sub-scanning direction is disposed near the surface to be scanned. ing. On the other hand, the radius of curvature of the cross section in the sub-scanning direction increases as the distance from the vicinity of the optical axis increases in the main scanning direction, but may decrease again in the middle.

The optical scanning device according to the present invention includes:
The present invention is not limited to the above-described embodiment, and various changes can be made. For example, the radii of curvature _RH and R
_V and the lens interval (or lens thickness) D can be changed as appropriate.

Further, when the absolute value | β _V | of the magnification in the sub-scanning direction section between the light polarization reflection surface 4 and the surface to be scanned 7 becomes large and exceeds, for example, 2, the position error of the light polarization reflection surface becomes large. Is enlarged, and the beam spot position on the surface to be scanned fluctuates greatly. When | β _V | decreases and becomes smaller than 0.5, for example, the traveling angle of the light beam reaching the vicinity of the scanned surface due to the inclination of the light polarization reflecting surface in the sub-scanning direction is enlarged, and the position of the scanned surface is shifted along the optical axis. If the beam spot position fluctuates, the beam spot position greatly fluctuates, resulting in uneven printing. On the other hand, in the above embodiment,
Since the magnification β _{V of the} cross section in the sub-scanning direction between the light polarization reflection surface 4 and the surface to be scanned 7 is in the range of 1 <| β _V | <2, a good image without printing unevenness can be obtained. .

Incidentally, the second lens _{L 2} of the above embodiment the main scanning cross section in the vicinity of the optical axis, _{5 <|} has a weak negative refractive power in the range of | _f 2H _/ f H. The numerical values in each embodiment are shown in the above-described tables.

[0044]

As described above, according to the optical scanning device of the present invention, the second image forming optical system including two lenses disposed between the light deflecting means and the surface to be scanned. The lens disposed on the scanned surface side has one surface which is a toric surface having a convex cross-section in the sub-scanning direction and having a rotation axis orthogonal to the optical axis and the main scanning direction, and the other surface being Has a non-arc shape whose cross section in the main scanning direction is substantially linear or concave near the optical axis, has a substantially straight or convex shape in the sub scanning direction, and has a rotation axis orthogonal to the optical axis and parallel to the main scanning direction. (Including the radius of rotation ∞), and the lens as a whole has a weak cross section in the main scanning direction near the optical axis and a cross section in the sub scanning direction having a positive refractive power.
It is possible to make the beam spot size uniform on the surface to be scanned while ensuring constant velocity in the main scanning direction.

In the second image forming optical system, the lens arranged on the light deflecting means side has a surface on the light deflecting means side having a cross section in the main scanning direction having a circular or non-circular curved line. It is a shape that is rotated with a rotation axis that is orthogonal to the main scanning direction, and the surface on the scanned surface side is formed of a toric surface having an optical axis and a rotation axis that is orthogonal to the main scanning direction. By doing so, it is possible to further uniform the beam spot size on the scanned surface in synergy with the effect of the lens disposed on the scanned surface side described above.

In the lens provided on the light deflecting means side, the cross section in the main scanning direction and the cross section in the sub scanning direction have a positive refractive power, and the surface on the scanning surface side has a meniscus shape convex near the optical axis. In this configuration, the incident angle and the outgoing angle of the light beam with respect to the lens can be made relatively small, and the tolerance of an error in the lens processing can be increased.

Further, when the second imaging optical system is constituted by lenses made of a plastic material, the workability of each lens is improved, the manufacture is facilitated, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an optical scanning device according to an embodiment of the present invention.

FIG. 2 illustrates an optical scanning device according to an embodiment of the present invention.
Configuration diagram of second imaging optical system

FIG. 3 is an aberration diagram of an optical system in the optical scanning device according to the first embodiment.

FIG. 4 is an aberration diagram of an optical system in the optical scanning device according to the second embodiment.

FIG. 5 is an aberration diagram of an optical system in the optical scanning device according to the third embodiment.

[Explanation of symbols]

L ₁ ~L ₂ second subscanning direction curvature radius D ₀ to D ₃ lens curvature in the main scanning direction radius R _V1 to R _V4 lens surface of the lens R _H1 to R _H4 lens surfaces constituting the imaging optical system Surface distance (lens thickness) 1 Light source 2 Collimator lens 3 Cylindrical lens 4 Light deflection / reflection surface 5 Polygon mirror 6 Second imaging optical system 7 Scanned surface

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 13/18 B41J 3/00 D H04N 1/113 H04N 1/04 104A F-term (Reference) 2C362 AA26 BA86 BB14 BB22 2H045 AA01 CA04 CA34 CA55 CA68 CB15 2H087 KA19 LA22 PA02 PA17 PB02 QA03 QA06 QA12 QA22 QA37 QA41 RA05 RA08 RA12 RA13 UA01 5C072 CA02 CA06 DA02 DA21 DA23 HA02 HA09 HA13 HB10 XA05

Claims (5)

[Claims] A collimator lens for emitting a light beam from a light source as a substantially parallel light beam; a first imaging optical system for forming an image of the light beam in a sub-scanning direction at a predetermined position; An optical scanning device comprising: a light deflecting unit having a light deflecting / reflecting surface disposed thereon; and a second imaging optical system for forming an image of a light beam reflected and deflected by the light deflecting unit on a surface to be scanned. The second imaging optical system is composed of two lenses. Of these, one of the lenses disposed on the surface to be scanned has a convex cross section in the sub-scanning direction, and the optical axis and the main scanning direction. A toric surface having a rotation axis orthogonal to the direction, the other surface is a non-arc shape in which the cross section in the main scanning direction forms a substantially straight or concave shape near the optical axis, the cross section in the sub scanning direction is a substantially straight or convex shape, Perpendicular to the optical axis and parallel to the main scanning direction An optical scanning device having a shape having a rotation axis (including a radius of rotation ∞), wherein the entire lens has a negative refractive power near the optical axis in the main scanning direction and a positive refractive power in the sub-scanning direction. . 2. A lens disposed on the surface to be scanned in the second imaging optical system, wherein the surface on the side of the light deflecting means has a convex cross section in the main scanning direction and a convex cross section in the sub scanning direction. In the toric surface having a rotation axis orthogonal to the optical axis and the main scanning direction, the surface on the surface to be scanned, the cross section in the main scanning direction is away from the optical axis in a concave shape on the surface to be scanned near the optical axis. Accordingly, the non-arc shape having a convex shape on the surface to be scanned has a shape in which the cross section in the sub-scanning direction has an extremely large radius of curvature, and the cross section in the main scanning direction is weak near the optical axis as a whole of the lens. The optical scanning device according to claim 1, wherein the cross section has a positive refractive power. 3. A lens provided on the surface to be scanned in the second imaging optical system, wherein the surface on the side of the light deflecting means has a substantially straight section in the main scanning direction near the optical axis; Is a deformed cylindrical surface having a rotation axis orthogonal to the optical axis and parallel to the main scanning direction, such that the non-arc shape approaches the scanning surface side as it moves away from the scanning surface, and the cross section in the sub-scanning direction forms a convex shape. The surface on the scanning surface side is a toric surface having a concave section in the main scanning direction, a convex section in the sub-scanning direction, and having a rotation axis orthogonal to the optical axis and the main scanning direction. 2. The optical scanning device according to claim 1, wherein the cross section in the main scanning direction has a weak negative refractive power, and the cross section in the sub scanning direction has a positive refractive power. 4. A lens provided in the second image forming optical system on the side of the light deflecting means, wherein a surface on the side of the light deflecting means has a cross section in a main scanning direction having an arc or a non-arc shape. It is a shape rotated by a rotation axis that is orthogonal to the axis and parallel to the main scanning direction, and the surface on the scanned surface side is
A toric surface having a rotation axis orthogonal to the optical axis and the main scanning direction; the lens as a whole having a positive refractive power in both the main scanning direction cross section and the sub scanning direction cross section; The optical scanning device according to any one of claims 1 to 3, wherein the optical scanning device has a convex meniscus shape in the vicinity. 5. The optical scanning device according to claim 1, wherein each lens constituting the second imaging optical system is made of a plastic material.