JPH103051A - Optical scanning lens and optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the function for keeping constant speed and the curvature of field in the main scanning direction, and to effectively prevent the generation of an erroneous shape in the molding process of an optical scanning lens. SOLUTION: The optical scanning lens 18 is composed of a biconvex single lens, molded from plastic. By representing the coordinates in the direction of optical axis by X, the coordinates in the direction orthogonal to the optical axis by Y, the radius of paraxial curvature by R, a conical constant by K and higher order coefficients by A, B, C, D..., the shapes in the deflection plane of a first and a second lens surfaces counted from the side of an optical deflector are non-circular-arc shapes specified by giving R, K, A, B, C, D in the relation: X=Y<2> /[R+R.√ 1-(1+K)Y<2> /R<2> }]+A.Y<4> + B.Y<6> +C.Y<8> +D.Y<10> +... and, by representing effective main scanning width by W, the thickness on the optical axis by d1 and a distance on the optical axis from the starting point of deflection by the optical deflector to the surface to be scanned by L; W, d1 , L satisfy the condition: (1) W/L>0.9, (2) 10<(W/L)<2> .(L/d1 )<30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical scanning lens and an optical scanning device.

[0002]

2. Description of the Related Art A light beam from a light source is deflected at an equal angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. Optical scanning devices for scanning are widely known in relation to optical printers, digital copiers and the like.

In such an optical scanning device, an arbitrary position on the "virtual optical path in which the optical path from the light source to the surface to be scanned is linearly developed along the optical axis" corresponds to the position parallel to the main scanning direction. The direction corresponding to the main scanning direction is referred to as “main scanning corresponding direction”, and the direction corresponding to the arbitrary position on the optical path in parallel with the sub scanning direction is referred to as “sub scanning corresponding direction”.

The scanning imaging lens has a function of condensing the deflected light beam on the surface to be scanned in the main / sub-scanning corresponding direction, but has a "constant speed function" for equalizing the optical scanning in the main scanning corresponding direction. ”Is required, and“ field curvature in the main scanning direction ”needs to be satisfactorily corrected so that the light spot diameter in the main scanning direction does not greatly vary with the image height.

It is intended to reduce the number of components of the scanning image forming lens by reducing the number of components of the scanning image forming lens by providing the function of at least the main scanning direction in the scanning image forming lens to one lens. Have been. A single lens having a necessary function in the main scanning corresponding direction in the scanning image forming lens is referred to as an “optical scanning lens” in this specification.

[0006] In order to achieve a uniform velocity function, which is a function necessary in the main scanning direction, and to correct field curvature satisfactorily by using one optical scanning lens, at least the optical scanning lens is required. "A shape different from a circular arc" is required as a shape of one surface in the main scanning corresponding direction. The optical scanning lens is generally a convex lens because it has a function of converging a deflected light beam on the surface to be scanned in the main scanning direction.

As described above, since the light scanning lens requires a complicated shape different from an arc on at least one surface, a molding process using a plastic material is suitable for manufacturing the light scanning lens. If configured as
The lens thickness tends to increase at the paraxial portion, or the thickness difference between the paraxial portion and the peripheral portion tends to increase.

[0008] For this reason, when manufacturing an optical scanning lens by plastic molding, there is a problem that a shape error such as "sinking or undulation" tends to occur. When such a shape error occurs, the actual performance is significantly deteriorated, no matter how excellent the design performance is. This problem,
When widening the scanning imaging lens to make the optical scanning device more compact and expand the optical scanning area, the optical scanning lens should be placed near the optical deflector to prevent the scanning imaging lens from becoming large. In particular, it tends to be noticeable.

Further, when the optical scanning lens has a single lens configuration, it is particularly effective to improve the constant velocity function by making the lens surface on the side of the optical deflector convex. However, when the lens surface on the optical deflector side is a convex surface, the "edge thickness" of the lens decreases as the radius of curvature decreases, and the thickness difference between the paraxial portion and the peripheral portion tends to increase. Likely to happen. If the radius of curvature of the lens surface on the optical deflector side is small, the angle of incidence of the deflected light beam on the lens surface (the outward normal of the lens surface and the incident deflection) increases toward the lens periphery in the main scanning direction. The angle formed by the light beam with the principal ray is likely to be large, and the field curvature and the deterioration of the uniform velocity due to the shape error of the lens surface are likely to occur.

[0010]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention improves the uniformity function and the curvature of field in the main scanning direction in an optical scanning lens, and reduces the shape error in the molding processing of the optical scanning lens. It is an object to effectively prevent occurrence.

Another object of the present invention is to reduce the size and cost of an optical scanning device by using the above-described optical scanning lens.

[0012]

The "optical scanning lens" in this specification condenses a deflecting light beam deflected at an equal angular velocity by an optical deflector on a surface to be scanned in a direction corresponding to the main scanning. This is a single lens having the function of making the main scanning of the scanning surface uniform.

The optical scanning lens according to the first aspect of the present invention has the following features.

That is, the optical scanning lens has a “biconvex single lens configuration” and is “molded with plastic”. For both the first and second lens surfaces counted from the optical deflector, the “shape within the deflecting surface” is such that the coordinates in the optical axis direction are X, the coordinates in the optical axis orthogonal direction are Y, and the paraxial radius of curvature is R. , The conic constant K,
A, B, C, D,. . . X = Y ² / [R + R · {{1- (1 + K) Y ² / R ² }] + A ·
^{Y 4 + B · Y 6 +} C · Y 8 + D · Y 10 +. . . R, K, A, B, C, D,. . . And the “non-circular shape” specified.

The "deflection surface" is a plane on which the principal ray of the deflected light beam ideally deflected by the optical deflector is swept.

The effective main scanning width is W, the thickness on the optical axis is d ₁ ,
When the distance on the optical axis from the starting point of deflection by the optical deflector (reflection position of the deflected light beam when the deflection angle is 0) to the surface to be scanned is L, these W, d ₁ , and L are the following conditions: W / L> 0.9 (2) 10 <(W / L) ² · (L / d ₁ ) <30 is satisfied.

"Effective main scanning width" means a width of a region set as a region where optical writing is performed favorably in a scanning region where main scanning is performed by a light spot, and is generally determined as a design condition of an optical scanning device. .

In the condition (1), (W / L) is “the optical path length from the optical deflector when the image height is 0 to the surface to be scanned: L
The ratio of the effective main scanning width: W to the optical scanning device becomes larger, and the larger the ratio, the more compact the optical scanning device and the wider the angle of view.
Therefore, when the lower limit of the condition (1): 0.9 is exceeded, it becomes difficult to realize a compact optical scanning device and a wide effective main scanning area.

In order to make the optical scanning device compact and to realize a compact optical scanning device using an optical scanning lens with a small difference in thickness, the ratio of the optical path length: L to the thickness: d ₁ : (L / d ₁ ) and the parameter of condition (1): (W / d ₁ )
It is desirable that the product of L) and the square is set within a certain range.

Parameter in condition (2): (W / L) ²
-As (L / d ₁ ) decreases, the lens thickness: d ₁ increases, and the “difference in thickness between the paraxial portion and the peripheral portion” increases,
It becomes a disadvantageous shape for plastic molding. When the value is below the lower limit of the condition (2): 10, the above-mentioned "disadvantage" becomes remarkable, and it becomes difficult to prevent the occurrence of shape errors such as "sinks and undulations" during molding.

As the above parameter in the condition (2) becomes larger, the lens thickness becomes smaller, and the optical scanning lens becomes thinner, which is advantageous for molding. However, since the lens becomes thinner, the field curvature becomes better. It is disadvantageous for realizing a proper correction and a good constant velocity function.

If the upper limit of condition (2) exceeds 30, it becomes difficult to realize a good correction of the curvature of field in the main scanning direction and a good function of equalizing the speed.

When the light beam incident on the light scanning lens is a “parallel light beam in the main scanning corresponding direction”, that is, when the light scanning lens is used as an fθ lens, condition (2)
However, this is a strong limitation on design freedom.

That is, in order to satisfy the above condition (2) when the light incident on the optical scanning lens is a “parallel light beam”,
Assuming that the distance on the optical axis from the starting point of the deflection to the first lens surface is d ₀ , and the distance on the optical axis from the second lens surface to the surface to be scanned is d ₂ , these ratios are d: ₀ / d ₂ is limited to “near 0.2”, and the arrangement position of the optical scanning lens is strongly restricted.

In order to avoid such a design limitation on satisfying the condition (2), the light beam incident on the optical scanning lens should be “a divergent or convergent light beam in the main scanning corresponding direction”. When “divergent light flux” is used in the main scanning corresponding direction, the condition (3) is satisfied by satisfying d ₀ / d ₂ <0.2 (claim 2). When the “convergent light beam” is incident on the optical scanning lens in the main scanning corresponding direction, the following condition is satisfied: (4) d ₀ / d ₂ > 0.2 Thereby (claim 3), the condition (2) can be easily satisfied.

According to the fourth aspect of the present invention, there is provided an optical scanning device comprising:
An optical scanning device that deflects a light beam from a light source at an equal angular velocity by an optical deflector, condenses the deflected light beam as a light spot on a surface to be scanned by a scanning image forming lens, and optically scans the surface to be scanned at a constant speed. Wherein the scanning imaging lens includes the optical scanning lens according to claim 1.

According to a fifth aspect of the present invention, there is provided an optical scanning device comprising:
An optical scanning device that deflects a light beam from a light source at an equal angular velocity by an optical deflector, condenses the deflected light beam as a light spot on a surface to be scanned by a scanning image forming lens, and optically scans the surface to be scanned at a constant speed. Wherein the deflected light beam enters the optical scanning lens as “a light beam diverging in the main scanning direction”, and the scanning image forming lens includes the optical scanning lens according to claim 2.

The "optical scanning device" of the invention according to claim 6 is
An optical scanning device that deflects a light beam from a light source at an equal angular velocity by an optical deflector, condenses the deflected light beam as a light spot on a surface to be scanned by a scanning image forming lens, and optically scans the surface to be scanned at a constant speed. Wherein the deflected light beam enters the optical scanning lens as “a light beam converging in the main scanning corresponding direction”, and the scanning image forming lens includes the optical scanning lens according to claim 3.

The "optical scanning device" of the invention according to claim 7 is:
An optical scanning device that deflects a light beam from a light source at an equal angular velocity by an optical deflector, condenses the deflected light beam as a light spot on a surface to be scanned by a scanning image forming lens, and optically scans the surface to be scanned at a constant speed. And a `` line image forming optical system '' for forming a light beam from the light source as a long line image in the main scanning corresponding direction in the vicinity of the deflecting and reflecting surface of the optical deflector. The optical scanning lens according to any one of 1, 2, and 3, wherein the optical scanning lens has a function of providing a geometrically conjugate relationship between a line image forming position and a surface to be scanned in the sub-scanning corresponding direction. And

In each of the optical scanning devices described in claims 4 to 7, "the scanning imaging lens includes an optical scanning lens" means that the scanning imaging lens is an optical scanning lens and at least one other lens. And the case where the optical scanning lens is the “scanning imaging lens itself”, that is, the case where the scanning imaging lens itself has a single lens configuration. .

It is necessary for the scanning imaging lens to properly correct the field curvature in the sub-scanning direction so that the light spot diameter in the sub-scanning direction does not fluctuate greatly with the image height in the "sub-scanning corresponding direction". In the optical scanning device according to the seventh aspect of the invention, in order to correct so-called "surface tilt" in the optical deflector, the position of the line image and the position of the surface to be scanned are geometrically conjugated. A “conjugate function” to be related is required.

The satisfactory correction of the field curvature in the sub-scanning direction and the satisfaction of the conjugate function can be realized by an optical scanning lens and one or more lenses added thereto. When the lens is the scanning imaging lens itself, it is possible to optimize the lens surface shape of at least one lens surface of the optical scanning lens in the sub-scanning corresponding direction according to the above-described field curvature correction and conjugate function. it can.

The optical scanning lens according to the present invention has the following features. That is, it is “a single ball configuration in which at least the lens surface on the optical deflector side has a convex shape in the paraxial region in the deflection surface” and is “molded with plastic”. Counting from the optical deflector side, the shape in the deflecting surface of both the first and second lens surfaces is represented by coordinates X and X in the optical axis direction.
The coordinates in the direction perpendicular to the optical axis are Y, the paraxial radius of curvature is R, the conic constant is K, and the higher order coefficients are A, B, C, D,. . . X = Y ² / [R + R · {{1- (1 + K) Y ² / R ² }] + A ·
^{Y 4 + B · Y 6 +} C · Y 8 + D · Y 10. . . R, K, A, B, C, D,. . . And the “non-circular shape” specified.

The effective main scanning width is W, the thickness on the optical axis is d ₁ ,
Assuming that the distance on the optical axis from the origin of deflection by the optical deflector to the surface to be scanned is L, these W, d ₁ , and L are conditions: (1A) W / L> 0.9 (2A) 10 < (W / L) ² · (L / d ₁ ) <30. Further, the focal length in the deflection plane is fm,
When the paraxial curvature radius is R ₁ in the first lens surface of the deflection plane as counted from the light deflector side, they conditions: a (5) 1.0 <R ₁ /fm<3.0 To be satisfied.

Therefore, the optical scanning lens according to the eighth aspect has the following differences from the optical scanning lens according to the first aspect. That is, first, the optical scanning lens according to claim 1 is a “biconvex lens”, whereas the optical scanning lens according to claim 8 is a second lens surface counted from the optical deflector side. The shape may be a shape other than the convex shape in the deflection plane. Second, the optical scanning lens according to claim 8 is:
The condition (5) is satisfied. The convex shape in the deflection surface refers to a shape in which the lens surface shape in the deflection surface is convex toward the outside of the lens.

Therefore, the shape in the sub-scanning corresponding direction is
The first lens surface counted from the optical deflector side can also have a concave shape (a shape concave toward the inside of the lens).

The conditions (1A) and (2A) are the conditions (1) and (2) for the optical scanning lens described in the first embodiment, respectively.
It is the same as (2) and has the same meaning.

Parameter in condition (5): R ₁ / fm
Exceeds the upper limit of 3.0, it is difficult to adjust the distortion, and it is difficult to improve the “constant velocity function” for realizing constant velocity of optical scanning. When the above parameter in the condition (5) exceeds the lower limit of 1.0, the thickness of the optical scanning lens is increased, or the difference in thickness between the paraxial portion and the peripheral portion is apt to increase. It is easy to generate undulations.
In addition, the angle of incidence of the deflected light beam on the lens surface on the optical deflector side becomes large in the peripheral portion in the main scanning direction, and the measurement error and the shape change due to environmental fluctuation (the plastic lens is deformed under the influence of temperature and humidity) ) Easily occurs.

The increase in the wall thickness and the wall thickness difference becomes more remarkable as the parameter: R ₁ / fm becomes smaller. Claim 8
As in the case of the optical scanning lens according to the invention described above, in the case where the shape of the second lens surface counted from the optical deflector side also allows “shape other than convex”, the lower limit is 1.0 as described above. However, when the lens shape is “biconvex” as in the optical scanning lens according to the first aspect of the present invention, the parameter: R ₁ /
The lower limit of fm is allowed up to about 0.5. Also in the optical scanning lens according to the eighth aspect, the “portion near the optical axis in the deflecting surface can be made biconvex”. When the shape within the deflection surface is a biconvex shape, the positive power of the optical scanning lens in the main scanning direction can be distributed to both surfaces, so that the radius of curvature of the lens surface on the optical deflector side within the deflection surface can be improved. Can be set large.

Also in the optical scanning lens according to the present invention, the distance on the optical axis from the starting point of the deflection to the first lens surface is d ₀ , and the distance from the second lens surface to the surface to be scanned is when the distance on the leading optical axis and d _2, d ₀ and d ₂ and the condition: (6) 0.1 <by so as to satisfy the d ₀ / d ₂ <0.3, the main scanning When a light flux substantially parallel to the corresponding direction is incident, the curvature of field in the main scanning direction and the function of equalizing the speed can be improved.
0).

In the case where the deflected light beam is incident on the optical scanning lens as a light beam converging in the main scanning direction, the above d ₀ and d ₂ are equivalent to the above condition (4): 4A) By satisfying d ₀ / d ₂ > 0.2, when a light beam substantially parallel to the main scanning corresponding direction is incident, the curvature of field in the main scanning direction and the function of equalizing the speed can be improved. (Claim 1
1). Furthermore, when the deflected light beam as incident on the optical scanning lens as a light flux diverging corresponding to the main scanning direction, the d ₀ and d ₂ and the _{condition: (7) d 0 / d} 2 <0.3 Is satisfied, the curvature of field in the main scanning direction and the function of equalizing the speed can be improved.
2).

According to a thirteenth aspect of the present invention, a light beam from a light source is deflected at a constant angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device for optically scanning the surface to be scanned at a constant speed, wherein the scanning image forming lens includes the optical scanning lens according to claim 8 or 9.

According to a fourteenth aspect of the present invention, a light beam from a light source is deflected at an equal angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. 11. An optical scanning device for optically scanning the surface to be scanned at a constant speed, wherein a deflected light beam is incident on an optical scanning lens as "a substantially parallel light beam in a main scanning corresponding direction", and a scanning image forming lens is provided. It is characterized by including the optical scanning lens described above.

According to a fifteenth aspect of the present invention, a light beam from a light source is deflected at an equal angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device that optically scans the surface to be scanned at a constant speed, wherein a deflected light beam is incident on the optical scanning lens as “a light beam converging in a main scanning corresponding direction”, and a scanning imaging lens is provided. The optical scanning lens according to the eleventh aspect is included.

According to a sixteenth aspect of the present invention, a light beam from a light source is deflected at a constant angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device for optically scanning the surface to be scanned at a constant speed, wherein the deflected light beam enters the optical scanning lens as "a light beam diverging in the main scanning corresponding direction", and the scanning imaging lens is provided. 12. An optical scanning lens according to claim 12.

According to a seventeenth aspect of the present invention, a light beam from a light source is deflected at an equal angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device that optically scans the surface to be scanned at a constant speed, wherein a light beam from a light source is formed as a long line image in a main scanning corresponding direction near a deflecting reflection surface of an optical deflector. An image optical system ", wherein the scanning image forming lens includes the optical scanning lens according to claim 8 or 9 or 10 or 11 or 12, and" the image forming position of the line image and A function of making the scanning plane a geometrically conjugate relationship with the scanning plane ".

In each of the optical scanning devices according to claims 13 to 17, "the scanning imaging lens includes an optical scanning lens" means that the scanning imaging lens includes the optical scanning lens and at least one other lens. This includes a case where the optical scanning lens is a “scanning imaging lens itself”, that is, a case where the scanning imaging lens itself has a single lens configuration.

It is necessary for the scanning imaging lens to properly correct the curvature of field in the sub-scanning direction so that the light spot diameter in the sub-scanning direction does not fluctuate greatly with the image height. In the case of the optical scanning device according to the seventeenth aspect of the present invention, the so-called "surface tilt" in the optical deflector.
In order to correct the above, a "conjugate function" is required which makes the image-forming position of the line image and the position of the surface to be scanned a geometrically conjugate relationship.

In each of the optical scanning devices according to the thirteenth to seventeenth aspects, the satisfactory correction of the curvature of field in the sub-scanning direction and the satisfaction of the conjugation function can be achieved by using an optical scanning lens and an additional lens. It can be realized by the above lens,
If the optical scanning lens is the scanning image forming lens itself, “optimize the lens surface shape of one or more lens surfaces of the optical scanning lens in the sub-scanning corresponding direction according to the above-described field curvature correction and conjugate function. You can do that. For this purpose, in each of the optical scanning lenses according to claims 8 to 12, at least one of the lens surfaces is referred to as “the power in the sub-scanning corresponding direction becomes greater as the optical axis moves away from the optical axis in the main scanning corresponding direction. It is effective to set the surface to be weaker and to make the optical scanning lens an anamorphic lens.

[0050]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments will be described below. Embodiment 1 of the optical scanning device according to claims 7 and 17
In FIG. 1 (a) showing the configuration, an LD 10
The divergent luminous flux emitted from is coupled with the LD 10 by the coupling lens 12 constituting a “light source”. A light beam from the light source is converged in a sub-scanning corresponding direction (a direction perpendicular to the drawing) by a convex cylinder lens 14 which is a “line image forming optical system”, and is deflected by a polygon mirror 16 which is an “optical deflector”. An image is formed in the vicinity as a long linear image in the main scanning direction, and is deflected at a constant angular velocity by the rotation of the polygon mirror 16.

The deflected light beam enters the optical scanning lens 18 forming the "scanning imaging lens itself", and the surface to be scanned 20 (a photoconductive photoreceptor is provided at that position) by the action of the optical scanning lens 18. The light is condensed as a light spot on the surface, and the surface to be scanned 20 is optically scanned in the main scanning direction (vertical direction in the figure). Distance: W is "effective main scanning width". The cylinder lens as the line image forming optical system can be replaced by a “concave cylinder mirror”.

In the embodiment shown in FIG. 1A, the coupling lens 12 has a function of converting the light beam from the LD 10 into a "weakly converging light beam". The deflection light beam having an angle of 0 is transmitted to the optical scanning lens 1.
If there is no 8, light is condensed on the natural light condensing point Q. "Natural focus point"
Indicates that the light flux coupled by the coupling lens forms a line image on this optical path in the aforementioned “virtual optical path in which the optical path from the light source to the surface to be scanned is linearly developed along the optical axis”. This is a position where light is naturally condensed when there is no image optical system or scanning image forming lens.

The distance from the deflecting reflection surface to the natural light converging point Q is represented by a distance: S as shown in the figure. When the natural focal point Q is on the scanning surface side with respect to the optical deflector, “S> 0”, and in this case, the coupled light beam is a weak convergent light beam. When the natural light converging point Q is closer to the light source than the optical deflector, “S <0”, and the light flux coupled at this time is weakly divergent. When the coupled light flux is a parallel light flux, “S = ∞”.

In FIG. 1A, X ₁ (Y) appears in the shape within the deflecting surface of the “first surface counted from the optical deflector side” (ie, in the drawing of FIG. 1A). Shape). X ₂ (Y) is “the second surface counted from the optical deflector side”
In the deflection plane.

In each of these, the coordinates in the optical axis direction are X, the coordinates in the optical axis orthogonal direction are Y, the paraxial radius of curvature is R, the conic constant is K, and the higher-order coefficients are A, B, C, D, . . X = Y ² / [R + R · {{1- (1 + K) Y ² / R ² }] + A ·
^{Y 4 + B · Y 6 +} C · Y 8 + D · Y 10. . . R, K, A, B, C, D,. . . And the “non-arc shape” specified.

Further, in the embodiment shown in FIG. 1A, since the optical scanning lens 18 forms the "scanning imaging lens itself", the sub-scanning corresponding direction is "line in the sub-scanning corresponding direction. It has a function of making the image forming position of the image and the scanned surface 18 a geometrically conjugate relationship, and has a shape that favorably corrects the field curvature in the sub-scanning direction. For this reason, the first and / or counting from the optical deflector side
Alternatively, the second lens surface is a “special toric surface” as shown in FIG. 1B or 1C. The sub-scanning direction of each surface of the optical scanning lens 1
The shape related to (the direction orthogonal to the drawing in FIG. 1A) is
As shown in FIG. 1A, they are symbolically represented by x ₁ (Y) and x ₂ (Y).

That is, in FIGS. 1B and 1C, the curves:
X (Y) represents the above-mentioned "non-circular shape (R is the paraxial radius of curvature in the above equation)". Figure 1 shows a special toric surface
As shown in (b) and (c), “the radius of curvature of the curvature circle in the sub-scanning corresponding direction: r according to each Y coordinate position of the non-arc shape
(Y) is a surface changed so as to improve the conjugate function and the correction of the curvature of field in the sub-scanning direction. At this time, a series of curvature centers at the curvature radius r (Y) is
It is generally a curve as shown by the chain line in the figure.

In each of the optical scanning lenses according to the first to third aspects, the non-circular shape in the deflecting surface is such that the first lens surface counted from the optical deflector side has a paraxial region in the paraxial region. The second lens surface is convex toward the surface to be scanned in the paraxial region. In each of the optical scanning lenses according to claims 8 to 12, the first lens surface counted from the optical deflector side is convex in the paraxial region toward the optical deflector side, and the second lens surface is The shape in the paraxial region can be other than convex to the surface to be scanned.

[0059]

EXAMPLES Hereinafter, 15 specific examples will be described.

In each embodiment, as shown in FIG. 1A, the light scanning lens 18 is moved from the starting point of deflection by the optical deflector.
The distance to the incident side surface of the optical scanning lens 18 is “d ₀ ”.
The thickness on the optical axis is “d ₁ ”, and the distance between the lens surface on the scanned surface 20 side and the scanned surface 20 is “d ₂ ”. Therefore, “L = d ₀ + d ₁ + d ₂ ”.

In the deflecting surface, the paraxial radii of curvature of the lens surfaces on the optical deflector side and the surface to be scanned side are defined as “R ₁ ” and “R ₂ ”, and the refractive index of the lens material (related to a wavelength of 780 nm). Represented by "N". Further, the focal length in the deflection plane is "fm".

The non-circular shape on the first lens surface counted from the optical deflector side: X ₁ (Y), R ₁ , K ₁ ,
The shape is specified by giving A ₁ , B ₁ , C ₁ , D _1, and the non-circular shape on the second lens surface counted from the optical deflector side: X
_{For 2} (Y), the shape is specified by giving R ₂ , K ₂ , A ₂ , B ₂ , C ₂ , and D ₂ .

When the first and / or second lens surface is the “special toric surface”,
For x ₁ (Y) = r ₁ (Y) and / or x ₂ (Y) = r ₂ (Y), deflection angles: θ = 0, 10, 20, 30, 36, 40,
45 degrees (θ = 10, 20, 30, 3 in Example 6)
4 degrees), the radius of curvature: r ₁ (θ) and / or
Alternatively, the shape is specified by giving r ₂ (θ). Note that Y and θ
Is related to: Y = d ₀ · θ.

Examples 1 to 6 relate to the optical scanning lenses according to the first to third aspects. In Examples 1 to 5, the effective main scanning width: W = 216 mm, the effective half angle of view: θm
ax = 45 degrees, and in the sixth embodiment, the effective main scanning width: W =
216 mm, effective half angle of view: θmax = 34 degrees.

Embodiment 1 In Embodiment 1, the light beam coupled by the coupling lens is a “parallel light beam”.

S = ∞, fm = 137.503 i R _i D _i N 0 29.887 1 137.503 12.364 1.53664 2-154.248 132.649 The lens surface on the optical deflector side is “common”. axis aspheric ", is rotationally symmetrical about the optical axis, symbolically" X ₁ to this (Y) = x ₁
(Y) ". The lens surface on the scanned surface side is a “special toric surface”.

X ₁ (Y): R ₁ = 137.503, K ₁ = −92.438, A ₁ =
−1.11822 × 10 to ⁶ , B ₁ = 7.28745 ×
10 to ¹⁰ , C ₁ = −3.20311 × 10 to ¹³ , D ₁ =
9.55204 × 10 ~ ^17.

X ₂ (Y): R ₂ = −154.248, K ₂ = 5.36873, A ₂
= −2.51300 × 10 ~ ⁶ , B ₂ = 1.95625
× 10 to ⁹ , C ₂ = −1.18490 × 10 to ¹² , D ₂ =
3.38372 × 10 ~ ^16.

R ₂ (θ): θ (degrees) 0 10 20 30 36 40 45 r ₂ -17.083 -17.243 -17.658 -18.116 -18.463 -18.607 -18.803

Fm = 137.503 (W / L) = 1.23, (W / L) ² · (L / d ₁ ) = 2
1.6, (d ₀ / d ₂ ) = 0.23
.

In Examples 2 and 3 below, the coupled luminous flux is weakly divergent, and thus “S
<0 ”. As in the first embodiment, the optical deflector side is a “coaxial aspherical surface”, and the scanned surface side is a “special toric surface”.

Example 2 S = -391.925, fm = 108.193 i R _i D _i N 0 22.381 1 108.193 10.000 1.53664 2 -121.259 142.519

X ₁ (Y) (= x ₁ (Y)): R ₁ = 108.503, K ₁ = −56.32541, A
₁ = -3.46610 × 10 ~ ⁶ , B ₁ = 1.98195
× 10 to ⁹ , C ₁ = −1.32194 × 10 to ¹³ , D ₁ =
5.00528 × 10 ~ ^17. X ₂ (Y): R ₂ = −121.259, K ₂ = 4.91312, A ₂
= -3.24924 × 10 ~ ⁶ , B ₂ = 1.444308
× 10 to ⁹ , C ₂ = -1.889357 × 10 to ¹² , D ₂ =
1.43613 × ^10-15 . r ₂ (θ): θ (degrees) 0 10 20 30 36 40 45 r ₂ -13.913 -14.070 -14.487 -14.979 -15.160 -15.181 -15.136

(W / L) = 1.23, (W / L) ^2.
(L / d ₁ ) = 26.7, (d ₀ / d ₂ ) = 0.16
.

[0075] Example 3 S = -796.535, fm = 125.223 i R i d i N 0 25.505 1 125.223 12.700 1.48578 2 -114.374 136.695.

X ₁ (Y) (= x ₁ (Y)): R ₁ = 125.223, K ₁ = −12.16377, A
₁ = −3.41094 × 10 ~ ⁶ , B ₁ = 1.79586
_{^{× 10 ~ 9, C 1 =}} -2.13309 × 10 ~ 13, D 1 =
1.22926 × 10 ~ ^16. X ₂ (Y): R ₂ = −114.374, K ₂ = 4.94342, A ₂
= -1.42312 × 10 ~ ⁶ , B ₂ = 1.07576
× 10 ~ ⁹ , C ₂ = -1.888925 × 10 ~ ¹² , D ₂ =
1.26201 × ^10-15 . r ₂ (θ): θ (degree) 0 10 20 30 36 40 45 r ₂ -13.246 -13.396 -13.815 -14.395 -14.717 -14.871 -15.096.

(W / L) = 1.23, (W / L) ^2.
(L / d ₁ ) = 21.0, (d ₀ / d ₂ ) = 0.19
.

In the following Examples 4 to 6, the coupled light flux has a weak convergence, and therefore “S
> 0 ". In Examples 4 and 5, the optical deflector side
The scanned surface side is a special toric surface.

[0079] Example 4 S = 551.935, fm = 168.191 i R i d i N 0 38.916 1 168.191 15.000 1.5370 2 -188.994 120.984.

X ₁ (Y): R ₁ = 168.191, K ₁ = −39.925, A ₁ =
_{^{-3.42235 × 10 ~ 7, B 1}} = 2.27288 ×
10 to ¹³ , C ₁ = 8.02089 × 10 to ¹⁵ , D ₁ = −
8.70591 × 10 ~ ^19. r ₁ (θ): θ (degrees) 0 10 20 30 36 40 45 r ₁ -31.000 -33.138 -45.561 -70.282 -81.839 -102.128 -126.958.

X ₂ (Y): R ₂ = −188.994, K ₂ = 4.83792, A ₂
^{= -4.98172 × 10 ~ 7, B} 2 = 7.72365
× 10 to ¹² , C ₂ = −1.63863 × 10 to ¹⁴ , D ₂ =
1.78271 × 10 ~ ^18. r ₂ (θ): θ (degrees) 0 10 20 30 36 40 45 r ₂ -13.910 -14.163 -15.245 -16.629 -16.990 -17.441 -17.540.

(W / L) = 1.23, (W / L) ^2.
(L / d ₁ ) = 17.8, (d ₀ / d ₂ ) = 0.46
.

[0083] Example 5 S = 316.745, fm = 200.243 i R i d i N 0 48.618 1 200.244 20.000 1.537664 2 -224.142 106.382.

X ₁ (Y): R ₁ = 200.244, K ₁ = -30.283, A ₁ =
−1.59263 × 10 to ⁷ , B ₁ = −4.04532 ×
_{^{10 ~ 12, C 1 = 6.02170}} × 10 ~ 15, D 1 = -
3.98571 × 10 ~ ^19. r ₁ (θ): θ (degrees) 0 10 20 30 36 40 45 r ₁ -30.000 -29.182 -28.764 -27.743 -26.556 -24.175 -17.022

X ₂ (Y): R ₂ = −224.142, K ₂ = 1.1990, A ₂
= −3.21262 × 10 ~ ⁷ , B ₂ = 7.0634
× 10 to ¹² , C ₂ = −9.24177 × 10 to ¹⁵ , D ₂ =
1.95829 × 10 ~ ^18. r ₂ (θ): θ (degree) 0 10 20 30 36 40 45 r ₂ -15.316 -15.232 -15.119 -14.531 -13.641 -12.436 -9.338

(W / L) = 1.23, (W / L) ^2.
(L / d ₁ ) = 13.3, (d ₀ / d ₂ ) = 0.37
.

In the sixth embodiment described below, the surface on the optical deflector side is “coaxial aspherical surface”, that is, X ₁ (Y) = x ₁ (Y), and the surface on the surface to be scanned is “special surface”. Toric surface ".

Example 6 S = + 728.528, fm = 225.700 i R _i D _i N 0 51.669 1 148.846 10.390 1.5241 2 -562.372 162.880

X ₁ (Y) (= x ₁ (Y)): R ₁ = 148.846, K ₁ = 5.4534, A ₁ =
−7.09267 × 10 to ⁷ , B ₁ = −2.21975 ×
10 to ¹⁰ , C ₁ = 6.07139 × 10 to ¹⁴ , D ₁ = −
8.33979 × 10 ~ ^18.

X ₂ (Y): R ₂ = −562.372, K ₂ = −462.3305A
₂ = −4.60398 × 10 ~ ⁷ , B ₂ = −2.89720
_{^{× 10 ~ 11, C 2 =}} -5.93656 × 10 ~ 14, D 2 =
1.73926 × 10 ~ ^17. r ₂ (θ): θ (degrees) 0 10 20 30 34 r ₂ -25.651 -26.163 -27.558 -28.895 -28.836

(W / L) = 0.96, (W / L) ^2.
(L / d ₁ ) = 19.9, (d ₀ / d ₂ ) = 0.32.
.

The special toric surface: r (Y)
Of "analytical expression" is, r (Y) = a + b · Y 2 + c · Y 4 + d · Y 6 + e · Y 8 + f
· In Y ¹⁰ + g · Y ^12, by substituting the value of the corresponding to each _{θ Y (= d 0 × θ} ), the coefficient: obtained solving in simultaneous equations a to g.

FIGS. 2 to 7 show diagrams of "field curvature" and "distortion" in Examples 1 to 6, respectively. The solid line in the figure of curvature of field relates to the main scanning direction, and the broken line relates to the sub-scanning direction. The curvature of field and distortion in the main scanning direction are satisfactorily corrected by the non-arc shapes: X ₁ (Y) and X ₂ (Y) that determine the shape of the deflection surface of the optical scanning lens. In Examples 4 and 5, both the curvature of field and the distortion in the main scanning direction are extremely good.

The distortion is related to the “function of equalizing the speed of light scanning”. The scanning speed of the light spot due to the deflecting light beam deflected at a uniform angular velocity tends to increase with an increase in the image height, and therefore, as shown in the figure, the positive distortion tends to increase in the portion where the image height increases. By doing so, good uniformity is realized. Further, the curvature of field in the sub-scanning direction is corrected very well by the "special toric surface" employed.

Embodiments 7 to 15 described below are claimed in claim 8.
It is an Example of the lens for optical scanning of-12. In Examples 7 to 15, counting from the optical deflector side, the first and second lens surfaces are both convex in the deflecting surface, and each surface is a special toric surface. That is,
The first lens surface counted from the optical deflector side is shown in FIG.
The second lens surface has a surface shape as shown in FIG. 1 (c).

In the following embodiments 7 to 15, only data relating to the performance (curvature of field and constant velocity function) in the direction corresponding to the main scanning, that is, only the shape data in the deflection plane are given.
Data in the sub-scanning corresponding direction, that is, the radius of curvature in the sub-scanning corresponding direction at the coordinate Y for the main scanning corresponding direction: r (Y)
Is optimized for each embodiment.

Example 7 S = ∞, fm = 139.256 i R _i D _i N 0 33.047 1 153.181 11.223 1.57210 2 -161.581 134.898

X ₁ (Y): R ₁ = 153.181, K ₁ = -15.522, A ₁ =
_{^{-4.90025 × 10 ~ 7, B 1}} = -3.62007 ×
10 to ¹¹ , C ₁ = 1.57778 × 10 to ¹⁴ , D ₁ =
4.52347 × 10 ~ ^18.

X ₂ (Y): R ₂ = −161.581, K ₂ = 4.90839, A ₂
= 2.3522 × 10 ~ ⁸ , B ₂ = −1.60484.
× 10 to ¹⁰ , C ₂ = −5.1123 × 10 to ¹⁴ , D ₂ =
1.59010 × 10 ~ ^17. (W / L) = 1.17, (W / L) ² · (L / d ₁ ) = 2
1.9, (d ₀ / d ₂ ) = 0.24, R ₁ /fm=1.1
.

Example 8 S = ∞, fm = 137.047 i R _i D _i N 0 34.511 1 274.091 12.45 1.57210 2 −108.062 133.443

X ₁ (Y): R ₁ = 274.094, K ₁ = −0.488153, A
₁ = −3.90047 × 10 to ⁷ , B ₁ = −3.664736
× 10 to ¹¹ , C ₁ = 1.52644 × 10 to ¹⁴ , D ₁ = −
4.46187 × 10 ~ ^18.

X ₂ (Y): R ₂ = −108.062, K ₂ = 2.99552, A ₂
^{= 3.11749 × 10 ~ 7, B} 2 = 2.04686
× 10 to ¹¹ , C ₂ = −4.65135 × 10 to ¹⁴ , D ₂ =
1.16507 × 10 ~ ^17. (W / L) = 1.17, (W / L) ² · (L / d ₁ ) = 2
0.3, (d ₀ / d ₂ ) = 0.26, R ₁ /fm=2.0
.

Example 9 S = ∞, fm = 137.041 i R _i D _i N 0 34.305 1 205.561 11.945 1.57210 2 -124.060 133.750

X ₁ (Y): R ₁ = 205.561, K ₁ = −4.42977, A ₁
^{= -4.58583 × 10 ~ 7, B} 1 = -3.92890
× 10 to ¹¹ , C ₁ = 1.47898 × 10 to ¹⁴ , D ₁ = −
8.64090 × 10 ~ ^19.

X ₂ (Y): R ₂ = −124.060, K ₂ = 3.52004, A ₂
^{= 3.24804 × 10 ~ 7, B} 2 = -9.05801
× 10 to ¹¹ , C ₂ = −4.80823 × 10 to ¹⁴ , D ₂ =
1.45322 × 10 ~ ^17. (W / L) = 1.17, (W / L) ² · (L / d ₁ ) = 2
0.5, (d ₀ / d ₂ ) = 0.26, R ₁ /fm=1.5
.

[0106] Example 10 S = 413.282, fm = 179.979 i R i d i N 0 42.725 1 197.976 17.897 1.51933 2 -171.592 114.304.

X ₁ (Y): R ₁ = 1977.976, K ₁ = 5.03422, A ₁
^{= -4.91745 × 10 ~ 7, B} 1 = -1.83806
_{^{× 10 ~ 11, C 1 =}} 1.63101 × 10 ~ 14, D 1 = -
8.38595 × 10 ~ ^19.

X ₂ (Y): R ₂ = −171.592, K ₂ = 4.60861, A ₂
= -3.38197 × 10 ~ ⁸ , B ₂ = 3.65873
× 10 to ¹¹ , C ₂ = −5.14531 × 10 to ¹⁴ , D ₂ =
1.28251 × 10 ~ ^17. (W / L) = 1.20, (W / L) ² · (L / d ₁ ) = 1
4.1, (d ₀ / d ₂ ) = 0.37, R ₁ /fm=1.1
.

[0109] Example 11 S = 492.845, fm = 168.271 i R i d i N 0 45.430 1 252.407 17.300 1.51933 2 -130.535 117.270.

X ₁ (Y): R ₁ = 252.407, K ₁ = 5.443257, A ₁
^{= -3.90428 × 10 ~ 7, B} 1 = -6.84195
× 10 to ¹² , C ₁ = 1.88037 × 10 to ¹⁴ , D ₁ = −
2.13891 × 10 ~ ^18.

X ₂ (Y): R ₂ = −130.535, K ₂ = −0.03984, A ₂
^{= 2.85512 × 10 ~ 8, B} 2 = 2.12059
× 10 to ¹¹ , C ₂ = −2.776749 × 10 to ¹⁴ , D ₂ =
1.01019 × 10 ~ ^17. (W / L) = 1.17, (W / L) ² · (L / d ₁ ) = 1
4.2, (d ₀ / d ₂ ) = 0.39, R ₁ /fm=1.5
.

Example 12 S = 746.803, fm = 156.939 i R _i D _i N 0 41.457 1 313.879 14.327 1.57210 2 -123.669 124.216

X ₁ (Y): R ₁ = 313.879, K ₁ = 11.6499, A
₁ = −2.71261 × 10 to ⁷ , B ₁ = −2.54808
_{^{× 10 ~ 11, C 1 =}} 1.96321 × 10 ~ 14, D 1 = -
2.73780 × 10 ~ ^18.

X ₂ (Y): R ₂ = −123.669, K ₂ = −0.03984, A ₂
= 1.30110 × 10 ~ ⁷ , B ₂ = 5.558410
× 10 to ¹¹ , C ₂ = −3.31374 × 10 to ¹⁴ , D ₂ =
1.13522 × 10 ~ ^17. (W / L) = 1.17, (W / L) ² · (L / d ₁ ) = 1
7.1, (d ₀ / d ₂ ) = 0.33, R ₁ /fm=2.0
.

[0115] Example 13 S = -1066.595, fm = 124.231 i R i d i N 0 27.989 1 136.654 10.110 1.57210 2 -144.109 136.660.

X ₁ (Y): R ₁ = 136.654, K ₁ = −89.8649, A ₁
= −3.582249 × 10 ~ ⁶ , B ₁ = 1.82151
× 10 ~ ⁹ , C ₁ = -1.84033 × 10 ~ ¹³ , D ₁ =
5.22868 × 10 ~ ^17.

X ₂ (Y): R ₂ = −144.109, K ₂ = 7.553274, A ₂
= -4.10849 × 10 ~ ⁶ , B ₂ = 2.30006
× 10 ~ ⁹ , C ₂ = -1.92530 × 10 ~ ¹² , D ₂ =
9.95898 × 10 ~ ^16. (W / L) = 1.20, (W / L) ² · (L / d ₁ ) = 2
5.0, (d ₀ / d ₂ ) = 0.20, R ₁ /fm=1.1
.

Example 14 S = -646.979, fm = 118.255 i R _i D _i N 0 28.8 1 177.382 10.725 1.57210 2 -106.959 140.375

X ₁ (Y): R ₁ = 177.382, K ₁ = −187.605, A ₁
= −3.29591 × 10 ~ ⁶ , B ₁ = 1.90010
× 10 to ⁹ , C ₁ = −1.889600 × 10 to ¹³ , D ₁ = −
2.05784 × 10 ~ ^17.

X ₂ (Y): R ₂ = -106.959, K ₂ = 5.99435, A ₂
^{= -3.44944 × 10 ~ 6, B} 2 = 2.49373
× 10 to ⁹ , C ₂ = −1.83255 × 10 to ¹² , D ₂ =
1.03695 × ^10-15 . (W / L) = 1.17, (W / L) ² · (L / d ₁ ) = 2
4.5, (d ₀ / d ₂ ) = 0.21, R ₁ /fm=1.5
.

[0121] Example 15 S = -607.344, fm = 117.840 i R i d i N 0 26.108 1 235.681 13.292 1.57210 2 -92.489 140.500.

X ₁ (Y) (= x ₁ (Y)): R ₁ = 235.681, K ₁ = −426.354, A ₁
^{= -3.07964 × 10 ~ 6, B} 1 = 2.02800
× 10 to ⁹ , C ₁ = −1.70546 × 10 to ¹³ , D ₁ = −
9.47523 × 10 ~ ^17.

X ₂ (Y): R ₂ = −92.489, K ₂ = 4.4119, A ₂ =
_{^{-2.74485 × 10 ~ 6, B 2}} = 2.50025 ×
10 to ⁹ , C ₂ = -1.83661 × 10 to ¹² , D ₂ =
1.05160 × ^10-15 . (W / L) = 1.17, (W / L) ² · (L / d ₁ ) = 1
8.44, (d ₀ / d ₂ ) = 0.19, R ₁ /fm=2.0
.

FIGS. 8 to 16 show diagrams of "field curvature" and "distortion" for Examples 7 to 15, respectively. Both the curvature of field and the distortion are related to the main scanning direction, and are well corrected by the non-circular shapes X ₁ (Y) and X ₂ (Y) which determine the shape in the deflection surface of the optical scanning lens. I have. As described above, since distortion is related to the “equalization function”,
The adjustment is made so that the uniform speed of the optical scanning becomes good.

[0125]

As described above, according to the present invention, a novel optical scanning lens and optical scanning device can be provided. As described above, the optical scanning lens of the present invention has a constant velocity function and a function of correcting the field curvature in the main scanning direction, which are required as functions of the scanning imaging lens in the main scanning direction, while having a single lens configuration. In addition, it is possible to effectively prevent the occurrence of a shape error at the time of molding with a plastic material.

In the optical scanning device of the present invention, by including the optical scanning lens in the scanning image forming lens, a compact and wide effective main scanning area can be realized, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram for describing an embodiment of an optical scanning device according to the present invention.

FIG. 2 is a diagram illustrating field curvature and distortion according to the first embodiment.

FIG. 3 is a diagram illustrating field curvature and distortion according to a second embodiment.

FIG. 4 is a diagram illustrating field curvature and distortion according to a third embodiment.

FIG. 5 is a diagram illustrating field curvature and distortion according to a fourth embodiment.

FIG. 6 is a diagram illustrating field curvature and distortion according to a fifth embodiment.

FIG. 7 is a diagram illustrating field curvature and distortion according to a sixth embodiment.

FIG. 8 is a diagram illustrating field curvature and distortion according to a seventh embodiment.

FIG. 9 is a diagram illustrating field curvature and distortion according to an eighth embodiment.

FIG. 10 is a diagram illustrating field curvature and distortion according to a ninth embodiment.

FIG. 11 is a diagram illustrating field curvature and distortion according to the tenth embodiment.

FIG. 12 is a diagram illustrating curvature of field and distortion according to the eleventh embodiment.

FIG. 13 is a diagram illustrating curvature of field and distortion according to the twelfth embodiment.

FIG. 14 is a diagram illustrating field curvature and distortion according to the thirteenth embodiment.

FIG. 15 is a diagram illustrating curvature of field and distortion according to the fourteenth embodiment.

FIG. 16 is a diagram illustrating curvature of field and distortion regarding Example 15;

[Explanation of symbols]

 Reference Signs List 10 LD 12 Coupling lens 14 Cylinder lens 16 Polygon mirror 18 Optical scanning lens 20 Scanned surface

Claims (17)

[Claims] 1. A lens having a function of converging a deflected light beam deflected at an equal angular velocity by an optical deflector on a surface to be scanned in a direction corresponding to the main scanning and making the main scanning on the surface to be scanned uniform. It has a biconvex single ball configuration, is molded from plastic, and the first and second lens surfaces, as counted from the optical deflector side, have the same shape in the deflection surface as the coordinates in the optical axis direction. X, the coordinate in the direction orthogonal to the optical axis is Y, the paraxial radius of curvature is R, the conic constant is K, and the higher order coefficients are A, B, C, D,. . . X = Y ² / [R + R · {{1- (1 + K) Y ² / R ² }] + A ·
^{Y 4 + B · Y 6 +} C · Y 8 + D · Y 10. . . R, K, A, B, C, D,. . The effective main scanning width is W, the thickness on the optical axis is d ₁ , and the distance on the optical axis from the starting point of deflection by the optical deflector to the surface to be scanned is W L
Where W, d ₁ and L satisfy the following condition: (1) W / L> 0.9 (2) 10 <(W / L) ² · (L / d ₁ ) <30 Optical scanning lens. 2. The optical scanning lens according to claim 1, wherein a distance on the optical axis from the starting point of the deflection to the first lens surface is d ₀ , and the distance from the second lens surface to the surface to be scanned is 2. Where d ₀ and d ₂ satisfy the condition (3) d ₀ / d ₂ <0.2, where d ₂ is the distance along the optical axis. 3. The optical scanning lens according to claim 1, wherein a distance on the optical axis from the starting point of the deflection to the first lens surface is d ₀ , and a distance from the second lens surface to the surface to be scanned is 3. Where d ₀ and d ₂ satisfy the condition (4) d ₀ / d ₂ > 0.2, where d ₂ is the distance along the optical axis. 4. A light beam from a light source is deflected at a constant angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device that performs optical scanning, wherein a scanning image forming lens includes the optical scanning lens according to claim 1. 5. A light beam from a light source is deflected at a constant angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device for performing optical scanning, wherein a deflected light beam is incident on the optical scanning lens as a divergent light beam in a main scanning corresponding direction, and the scanning imaging lens includes the optical scanning lens according to claim 2. Optical scanning device characterized by the following. 6. A light beam from a light source is deflected at a constant angular velocity by an optical deflector, and the deflected light beam is converged as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device that performs optical scanning, wherein a deflected light beam is incident on the optical scanning lens as a light beam converging in a main scanning corresponding direction, and the scanning imaging lens includes the optical scanning lens according to claim 3. Optical scanning device characterized by the following. 7. A light beam from a light source is deflected at a constant angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device for optically scanning, comprising: a line image forming optical system for forming a light beam from a light source as a long line image in a main scanning corresponding direction near a deflecting reflection surface of an optical deflector; Includes the optical scanning lens according to claim 1, 2 or 3, and
An optical scanning device having a function of setting the image forming position of the line image and the scanned surface in a geometrically conjugate relationship. 8. A lens having a function of converging a deflected light beam deflected at an equal angular velocity by an optical deflector on a surface to be scanned in a direction corresponding to the main scanning and making the main scanning on the surface to be scanned uniform. And at least the lens surface on the optical deflector side is within the deflection surface,
It is a single ball configuration having a convex shape in the paraxial region, is molded from plastic, and the first and second lens surfaces counted from the optical deflector side have the same shape in the deflection surface as the optical axis. The coordinates of the direction are X,
The coordinates in the direction perpendicular to the optical axis are Y, the paraxial radius of curvature is R, the conic constant is K, and the higher order coefficients are A, B, C, D,. . . X = Y ² / [R + R · {{1- (1 + K) Y ² / R ² }] + A ·
^{Y 4 + B · Y 6 +} C · Y 8 + D · Y 10. . . R, K, A, B, C, D,. . The effective main scanning width is W, the thickness on the optical axis is d ₁ , and the distance on the optical axis from the starting point of deflection by the optical deflector to the surface to be scanned is W L
Where W, d ₁ and L satisfy the following condition: (1A) W / L> 0.9 (2A) 10 <(W / L) ² · (L / d ₁ ) <30 When the focal length in the plane is fm, and the paraxial radius of curvature of the _first lens surface in the above-mentioned deflection surface, counted from the optical deflector side, is R1, these conditions are as follows: (5) 1.0 <R An optical scanning lens characterized by satisfying _{1 /} fm <3.0. 9. The optical scanning lens according to claim 8, wherein a portion near the optical axis has a biconvex shape. 10. The optical scanning lens according to claim 8, wherein the distance on the optical axis from the starting point of deflection to the first lens surface is d ₀ , and the distance from the second lens surface to the surface to be scanned. Where d ₂ is the distance on the optical axis that reaches d _2, and d ₀ and d ₂ satisfy the following condition: (6) 0.1 <d ₀ / d ₂ <0.3 Lens. 11. The optical scanning lens according to claim 8, wherein the distance on the optical axis from the starting point of deflection to the first lens surface is d ₀ , and the distance from the second lens surface to the surface to be scanned. Where d ₀ and d ₂ satisfy the condition: (4A) d ₀ / d ₂ > 0.2, where d ₂ is the distance on the optical axis that reaches. 12. The optical scanning lens according to claim 8, wherein a distance on the optical axis from the starting point of the deflection to the first lens surface is d ₀ , and a distance from the second lens surface to the surface to be scanned. Wherein d ₀ and d ₂ satisfy the following condition: d ₀ / d ₂ <0.3, where d ₂ is the distance on the optical axis reaching d. 13. A light beam from a light source is deflected at an equal angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device for performing optical scanning, wherein the scanning image forming lens includes the optical scanning lens according to claim 8. 14. A light beam from a light source is deflected at a constant angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device for performing optical scanning, wherein a deflected light beam is incident on the optical scanning lens as a substantially parallel light beam in a main scanning corresponding direction, and the scanning imaging lens includes the optical scanning lens according to claim 10. Optical scanning device. 15. A light beam from a light source is deflected at a constant angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device for performing optical scanning, wherein the deflected light beam is incident on the optical scanning lens as a converging light beam in a main scanning corresponding direction, and the scanning imaging lens includes the optical scanning lens according to claim 11. Optical scanning device characterized by the following. 16. A light beam from a light source is deflected at an equal angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device for performing optical scanning, wherein a deflected light beam is incident on the optical scanning lens as a divergent light beam in a main scanning corresponding direction, and the scanning image forming lens includes the optical scanning lens according to claim 12. Optical scanning device characterized by the following. 17. A light beam from a light source is deflected at an equal angular velocity by an optical deflector, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming lens. An optical scanning device for optically scanning, comprising: a line image forming optical system for forming a light beam from a light source as a long line image in a main scanning corresponding direction near a deflecting reflection surface of an optical deflector; Includes the optical scanning lens according to claim 8, 9, 10, 11, or 12, and geometrically optically conjugates the imaging position of the line image and the surface to be scanned with respect to the sub-scanning corresponding direction. An optical scanning device having a function of: