JPH09138365A - Lens for optical scanning, scanning and imaging lens, and optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relax the tolerance of an assembly common difference by composing the scanning and imaging lens of the lens for optical scanning which increases in the absolute value of the radius of curvature in a deflection orthogonal plane toward a maximum value with the distance from the optical axis and then decreases after exceeding the maximum value position. SOLUTION: The lens which is closest to a scanned surface 8 between lenses 6 and 7 is the lens for optical scanning. The lens 7 for optical scanning is a 'meniscus lens having its concave surface on the side of an optical deflector', and the surface on the side of the optical deflector is a 'barrel-shaped concave toroidal surface having an axis of rotation parallel to a main scan corresponding direction'. Further, the surface on the side of the scanned surface monotonously and smoothly increases in the absolute value of the radius of curvature in the deflection orthogonal plane toward the maximum value with the distance from the optical axis in the main scan corresponding direction and then decreases with the same tendency after exceeding the maximum value position. Further, the line obtained by connecting the centers of curvature in the deflection orthogonal plane on the side of the scanned surface is curved in the deflection plane along the main scan corresponding direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning lens, a scanning imaging lens, and an optical scanning device.

[0002]

2. Description of the Related Art A light beam imaged in a long line image in a main scanning direction is deflected at a constant angular velocity by an optical deflector having a deflecting / reflecting surface in the vicinity of the image forming position of the line image to scan the deflected light beam. An optical scanning device that converges a light spot on a surface to be scanned by an image lens to perform uniform optical scanning of the surface to be scanned is widely known in connection with optical printers and digital copying machines.

The "main scanning corresponding direction" corresponds to the main scanning direction in parallel on a virtual optical path in which the optical path from the light source to the surface to be scanned is linearly expanded along the optical axis of the optical system. A direction, which corresponds to a direction parallel to the sub-scanning direction on the virtual optical path, is called a “sub-scanning corresponding direction”.

The surface on which the principal ray of the deflected light beam ideally deflected by the optical deflector sweeps along with the deflection is referred to as a "deflection surface" in this specification. A plane that is orthogonal to the deflection surface and that is parallel to the optical axis of the scanning and imaging lens is called a "deflection orthogonal plane".

The scanning / imaging lens has a "conjugation function" for forming a "geometrically-optically conjugate relationship" with respect to the sub-scanning corresponding direction between the image forming position of the line image and the surface to be scanned, and optical scanning. It has a "constant speeding function" for speeding up. The conjugation function is a function for correcting the "face tilt" of the deflective reflection surface of the optical deflector.

In order to realize good optical scanning, the scanning and imaging lens must have good conjugation and constant velocity functions, as well as good correction of field curvature in the sub-scanning direction. is required. If the curvature of field in the sub-scanning direction is not sufficiently corrected, the diameter of the light spot in the sub-scanning direction will vary with the image height of the light spot, and the resolution of the written image will be significantly reduced, leading to a deterioration in image quality. .

In order to satisfactorily correct the field curvature in the sub-scanning direction, the radius of curvature in the plane orthogonal to the deflection is changed according to the position in the main scanning corresponding direction on one or more lens surfaces of the scanning imaging lens. A scanning imaging lens is known (for example, Japanese Patent Laid-Open No. 6-230308).

In the scanning and imaging lens described in the above publication, the field curvature in the sub-scanning direction is satisfactorily corrected, but the radius of curvature in the plane orthogonal to the deflection "monotonically increases with the distance from the optical axis in the main scanning corresponding direction." Therefore, the above-mentioned radius of curvature greatly differs between the deflection angle of 0 and the maximum deflection angle (corresponding to the end of the effective main scanning area). If a lens having such a surface shape has an assembling error such as decentering or shift, the assembling error significantly deteriorates the field curvature in the sub-scanning direction.

For this reason, the scanning and imaging lens described in the above publication has strict tolerances of assembly, which causes a problem of poor workability in assembling the optical scanning device.

[0010]

In view of the above-mentioned circumstances, the present invention provides an optical scanning device and a scanning imaging lens,
An object of the present invention is to realize a scanning imaging lens that can effectively relax the tolerance for the tolerance of the assembly to the optical scanning device while keeping the conjugation function and the constant velocity function satisfactorily.

[0011]

In the "optical scanning lens" of the present invention, a light beam formed into a long line image in the main scanning corresponding direction has a deflecting / reflecting surface near the image forming position of the line image. In an optical scanning device that deflects light beams at a constant angular velocity by an optical deflector, collects the deflected light beam as a light spot on a surface to be scanned by a scanning imaging lens, and performs uniform optical scanning of the surface to be scanned, a plurality of The lens forming a part of the scanning and imaging lens formed by the lens.

That is, the optical scanning lens is a single lens, and constitutes a scanning imaging lens together with one or more other lenses.

The optical scanning lens has the following features (claim 1).

That is, the optical scanning lens is a "meniscus lens having a concave surface facing the optical deflector", and the surface on the optical deflector side is "a concave barrel-shaped toroidal having a rotation axis parallel to the main scanning corresponding direction". The surface on the side of the surface to be scanned has the “maximum position where the absolute value of the radius of curvature in the plane orthogonal to the deflection increases smoothly and monotonically toward the maximum value as it leaves the optical axis in the main scanning corresponding direction. After passing, the line is defined so as to decrease smoothly and monotonically as it leaves the optical axis, and the line connecting the curvature centers in the plane orthogonal to the deflection of the surface to be scanned is in the main scanning corresponding direction in the deflection surface. It will be a curved line. "

Since the above-mentioned "optical scanning lens" is a meniscus lens, it is possible to "uniformize the thickness" by effectively reducing the thickness difference between the central portion and the peripheral portion, particularly the central portion and the peripheral portion in the main scanning corresponding direction. Therefore, it is possible to effectively prevent the deformation such as "sink or swell" when the resin such as plastic is formed by molding.

Since the optical scanning lens is arranged with the concave surface facing the optical deflector side, the "difference in lateral magnification in the sub scanning corresponding direction" between the central portion and the peripheral portion in the main scanning corresponding direction can be reduced.

The optical scanning lens according to claim 1 is another lens.
A "scanning imaging lens" is configured with one or more lenses. In this case, the optical scanning lens may be basically arranged at any part of the scanning / imaging lens, but it is “on the most scanned surface side among the plurality of lenses forming the scanning / imaging lens”. It can be deployed (Claim 2).

Since the deflected light beam is incident on the scanning image forming lens, in the case of a scanning image forming lens composed of two or more lenses, the effective diameter in the main scanning direction becomes larger as the lens is closer to the surface to be scanned. . Therefore, by disposing an optical scanning lens that can be easily molded of plastic or the like at a position closest to the surface to be scanned, it becomes possible to easily manufacture the scanning imaging lens.

In the optical scanning lens described in claim 2, the surface on the optical deflector side is a "barrel toroidal surface having a non-arcuate shape in the deflection surface", and the surface on the scanned surface side is "deflected". The in-plane shape can be "arc shape" (claim 3).

The "non-arcuate shape" has a coordinate: X in the optical axis direction and a coordinate: Y in the direction orthogonal to the optical axis, where R is the paraxial radius of curvature, K is the conic constant, and A is a higher-order coefficient. , B, C,
D,. . . X = (Y ² / R) / [1 + √ {1- (1 + K) (Y / R) ² }] + A · Y ⁴ + B · Y ⁶ + C · Y ⁸ + D · Y ¹⁰ . . . (1) R, K, A, B, C, D ,. . Is a curved shape specified by, and is "concave toward the optical deflector side" in the present invention.

A "concave barrel-shaped toroidal surface" is formed by rotating such a "non-arcuate shape or an arcuate shape" around a rotation axis parallel to the main scanning corresponding direction in the deflection surface.

According to a fourth aspect of the present invention, there is provided a scanning image forming lens, wherein a light beam imaged in a line image long in a main scanning direction is made to have an equal angular velocity by an optical deflector having a deflecting / reflecting surface near an image forming position of the line image. The scanning and imaging lens in the "optical scanning device for performing uniform optical scanning of the surface to be scanned by condensing the deflected light beam as a light spot on the surface to be scanned by the scanning and imaging lens". It is composed of one lens.

One of the two lenses is the optical scanning lens described in claim 3. The lens on the optical deflector side has a surface on the optical deflector side that is “a coaxial aspherical surface (a shape obtained by rotating the non-arc shape specified by the above formula (1) around the optical axis)”, The surface on the scanned surface side is a “spherical surface”.

According to a fifth aspect of the present invention, there is provided a scanning and image forming lens in which "a light beam imaged in a long line image in a main scanning direction is formed at an equal angular velocity by an optical deflector having a deflecting / reflecting surface near an image forming position of the line image. The scanning and imaging lens in the "optical scanning device for performing uniform optical scanning of the surface to be scanned by condensing the deflected light beam as a light spot on the surface to be scanned by the scanning and imaging lens". It is composed of one lens.

One of the two lenses is the optical scanning lens described in claim 3. The lens on the optical deflector side has a surface on the optical deflector side that is "a barrel-shaped toroidal surface having a non-arcuate shape in the deflecting surface and having a rotation axis parallel to the main scanning corresponding direction." Is the “normal toroidal surface”.

According to a sixth aspect of the present invention, there is provided an optical scanning device in which "a light beam formed into a long line image in the main scanning direction is formed at a constant angular velocity by an optical deflector having a deflecting / reflecting surface in the vicinity of an image forming position of the line image. An optical scanning device for deflecting the light beam and converging the deflected light beam as a light spot on the surface to be scanned by the scanning imaging lens to perform uniform optical scanning of the surface to be scanned ". The scanning imaging lens according to claim 1 or 2.
Alternatively, the optical scanning lens described in 3 is included.

According to a seventh aspect of the present invention, there is provided an optical scanning device in which "a light beam formed into a long line image in the main scanning direction is equiangularly moved by an optical deflector having a deflecting / reflecting surface near the image forming position of the line image. An optical scanning device for deflecting the light beam onto the surface to be scanned as a light spot by the scanning and imaging lens and performing uniform optical scanning of the surface to be scanned. It is the scanning imaging lens described in 4 or 5.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows an embodiment of an optical scanning device according to claims 6 and 7.

The laser beam emitted from the light source LD1 is coupled by the coupling lens 2 and is reflected by the mirror 4 while being condensed only in the sub-scanning corresponding direction (direction orthogonal to the drawing) by the cylinder lens 3. A long line image is formed at the position of the deflecting reflection surface 5 of the optical deflector in the main scanning corresponding direction (direction parallel to the drawing).

The mirror 4 may be omitted depending on the layout of the optical system extending from the LD 1 to the deflective reflection surface 5, and the cylinder lens 3 may be replaced by a "concave cylinder mirror".

In this embodiment, the optical deflector is a rotating single-sided mirror such as a "horizontal mirror", and its rotation axis 5A is included in the deflecting / reflecting surface 5, and the principal ray of the light beam from the light source side is It is incident on the position of the rotating shaft 5A. Therefore, in this embodiment, there is no occurrence of so-called "sag", which is a deviation between the deflection reflection surface 5 and the image forming position of the line image due to the rotation of the deflection reflection surface 5.

The light beam reflected by the deflecting / reflecting surface 5 is deflected at a constant angular velocity as the deflecting / reflecting surface 5 rotates at a constant speed, and becomes a deflected light beam and passes through the lenses 6 and 7. The lenses 6 and 7 form a "scanning / imaging lens".

The deflected light flux which has passed through the scanning and imaging lens is condensed toward the surface 8 to be scanned, and the surface 8 to be scanned is scanned at a constant speed by a light spot formed on the surface 8 to be scanned. Since a photoconductive photoconductor or the like is usually arranged at the position of the surface 8 to be scanned, the light spot actually optically scans the photoconductor.

In this embodiment, of the lenses 6 and 7, the lens 7 closest to the surface 8 to be scanned is the optical scanning lens. The optical scanning lens 7 is a “meniscus lens having a concave surface facing the optical deflector”, and the surface on the optical deflector side is a “concave barrel-shaped toroidal surface having a rotation axis parallel to the main scanning direction”. is there.

The barrel-shaped toroidal surface will be described with reference to FIG. In FIG. 2, the X axis is aligned with the optical axis of the scanning imaging lens, and the Y axis is parallel to the main scanning corresponding direction. Therefore, the XY plane is a "deflection surface".

The curve X (Y) shown in FIG. 2 is a curve in the deflection plane, and is "concave" toward the optical deflector side, that is, to the left in FIG. A curve: X (Y) is an “arc shape” or a “non-arc shape” specified by the above-mentioned formula (1).

The barrel-shaped toroidal surface is "a barrel-shaped curved surface obtained by rotating a curve: X (Y) around the rotation axis AX".
Since the rotation axis AX is on the left side of the curve: X (Y), that is, on the optical deflector side, the barrel-shaped toroidal surface formed is a concave surface.

Curve: The Y coordinate of an arbitrary point on X (Y) is Y =
If η, the absolute value of the radius of curvature: r (η) in the plane perpendicular to the deflection of the barrel-shaped toroidal surface (the plane parallel to the X axis among the planes orthogonal to the drawing) at this position is | r (η) | = | R
It is given by (0) |-| X (Y) |.

Therefore, in order to specify the barrel-shaped toroidal surface, it is sufficient to give the curves: X (Y) and r (0) (the radius of curvature in the plane orthogonal to the deflection including the optical axis).

The surface shape of the scanning surface side of the optical scanning lens 7 will be described with reference to FIG. In FIG. 3A, the X axis is aligned with the optical axis of the scanning imaging lens, and the Y axis is parallel to the main scanning corresponding direction. Therefore, the XY plane is a "deflection surface".

The curve X (Y) shown in FIG. 3 (a) is a curve in the deflecting / reflecting surface, passes through the coordinate origin, and goes toward the optical deflector side, that is, to the left in FIG. 3 (a). It is concave.

The curve: X (Y) is an "arc shape" or a "non-arc shape" specified by the above-mentioned equation (1).

Letting r (η) be the radius of curvature in the deflection orthogonal plane (plane parallel to the X-axis among planes orthogonal to the drawing) which is separated from the X-axis by the distance Y = η in the Y-axis direction, The surface on the scanning surface side has a maximum value as the absolute value of the radius of curvature r (η) in the plane orthogonal to the deflection deviates from the optical axis (matching the X axis) in the main scanning corresponding direction (parallel to the Y direction). It is determined to increase monotonously and smoothly toward the point, and after it exceeds the maximum position, it monotonically and smoothly decreases as it leaves the optical axis.
In addition, a line (shown by a chain line in FIG. 3A) connecting the centers of curvature in the plane orthogonal to the deflection of the surface to be scanned is the deflection surface (XY
It is set so as to form a curve L along the main scanning corresponding direction (Y-axis direction) in the plane.

Radius of curvature in the plane orthogonal to the deflection: The absolute value of r (η) "monotonically and smoothly increases toward the maximum value as it leaves the optical axis in the main scanning corresponding direction, and then exceeds the maximum position. , It decreases monotonically and smoothly as it goes away from the optical axis. "Therefore, the radius of curvature in FIG. 3A: r (0), r
As shown in FIG. 3 (b), the “difference” between the absolute values of (η) increases monotonously and smoothly toward the maximum as it leaves the X-axis in the Y direction. It decreases monotonously and smoothly with increasing distance.

FIG. 4 schematically shows another embodiment of the optical scanning device according to claims 6 and 7.

The laser beam emitted from the LD 1 is coupled by the coupling lens 2 and is condensed by the cylinder lens 3 only in the sub-scanning corresponding direction while being reflected by the mirror 4 and the deflection reflection surface 51 of the optical deflector 50. Is imaged as a long line image in the main scanning corresponding direction in the vicinity of. Similar to the embodiment of FIG. 1, the mirror 4 can be omitted depending on the layout of the optical system from the LD 1 to the deflective reflection surface 51, and the cylinder lens 3 can be replaced by a “concave cylinder mirror”.

In this embodiment, the optical deflector 50 is a "polygon mirror", and its rotation axis 53 is the deflective reflection surface 5.
It deviates from 1, and as the deflection reflection surface 51 rotates, a "sag" which is a deviation between the deflection reflection surface 51 and the image forming position of the line image occurs.

The light beam reflected by the deflecting / reflecting surface 51 is deflected at a constant angular velocity as the polygon mirror 50 rotates at a constant velocity.
It becomes a polarized light beam and passes through the lenses 60 and 70. These lenses 60 and 70 form a "scanning / imaging lens".

The deflected light flux that has passed through the scanning and imaging lens is condensed toward the surface to be scanned 8 to form a light spot on the surface to be scanned 8, and the surface to be scanned 8 (usually a photoconductive photosensitive member or the like). Are deployed) at a constant speed.

Also in this embodiment, of the lenses 60 and 70, the lens 70 closest to the surface 8 to be scanned is the optical scanning lens.

[0051]

EXAMPLES Hereinafter, specific examples for the embodiment shown in FIGS. 1 and 4 will be given one by one. Although not described above, the light flux coupled by the coupling lens 2 can be a “parallel light flux” or a “weakly converging light flux”, and is a “weakly divergent light flux”. You can also The scanning image forming lens is designed according to the above three types of light beam forms.

In Examples 1 and 2 described below, the light flux coupled by the coupling lens 2 is a "weakly convergent light flux".

As shown representatively in FIG. 1, the respective lens surfaces of the two lenses forming the scanning imaging lens are the first to fourth surfaces from the optical deflector side.

From the starting point of deflection by the optical deflector to the natural condensing point of the deflected light beam (the position on the optical axis where the "weakly converging deflected light beam" is naturally condensed without being affected by the optical element). The distance is S, the distance on the optical axis from the deflection starting point to the first surface is S ₀ , the distance on the optical axis between the second surface and the third surface is l ₁ , the fourth surface and the surface to be scanned. Let l ₂ be the distance on the optical axis between and. Further, the distance on the optical axis between the first and second surfaces (the thickness of the lens on the optical deflector side) is d ₁ , and the thickness of the lens on the surface to be scanned (optical scanning lens) is d ₂ . To do.

[0055] refractive index for the wavelength used for the material of the optical deflector side and the scan surface side lens (oscillation wavelength of LD1) respectively and "N _1, N _2". This is also followed in the embodiment of FIG. The unit for the quantity having the dimension of length is "mm".

Example 1 This is a specific example of the embodiment shown in FIG.

S = 300.2, S ₀ = 40, d ₁ = 19.
1, l ₁ = 35.0, d ₂ = 8, l ₂ = 70.9, N ₁ =
1.537, N ₂ = 1.537.

First surface Surface shape: coaxial aspherical surface (shape obtained by rotating the non-arcuate shape specified by the equation (1) around the optical axis) R = -335, K = 8.4, A = -5.93521E-
7, B = 2.42370E-10, C = -4.3E-
14, D = 1.3E-18 In the above value, E and the number following it represent "power". That is, for example, "E-7" means "10 to ⁷ ",
This power is applied to the value immediately before it. The same applies to the following.

Second surface Surface shape: spherical surface Radius of curvature: R = -78
.

Third surface: surface on the optical deflector side of the optical scanning lens Surface shape: concave barrel-shaped toroidal surface in which the shape in the deflection surface is a non-arc shape (see FIG. 2) Shape in deflection surface: X ( Y) R = -383, K = 9.9, A = 3.4244E-
7, B = -2.4985E-11, C = 8.9E-1
6, D = 2.2E-20 Radius of curvature in the plane orthogonal to the deflection on the optical axis: r (0) (FIG. 2)
Curve: distance between X (0) and rotation axis AX) r (0) =-30
.

Fourth surface: surface on the scanned surface side of the optical scanning lens Surface shape: surface shape described with reference to FIG. 3 Shape in deflection surface: X (Y) (arc shape) Curvature radius: R = -500 Curvature radius in the orthogonal plane of deflection: r (Y) Radius of curvature in the orthogonal plane of deflection with respect to the incident position: Y of the principal ray of the deflected light beam on the fourth surface in the main scanning corresponding direction (Y direction): r ( Y) at a typical incident position: Y = 0, 20.
2, 35.3, 62.3, 75.3 (mm), and image height: H and each image height when the curvature of field in the sub-scanning direction (unit: mm). It shows as a list.

Incident position: Y 0 20.2 35.3 62.3 75.3 Radius of curvature: r (Y) -14.26 -14.39 -14.54 -1
4.45-14.14 Image height: H 0.0 32.5 55.9 93.4 108.
9 Field curvature: 0.01 0.05 -0.08 -0.04 0.05.

In the embodiment of FIG. 1, no sag is generated by the optical deflector, and the radius of curvature: r (0) is "optical axis symmetric" in the Y direction.

As can be seen from this list, the radius of curvature of the fourth surface in the plane orthogonal to the deflection increases monotonically and smoothly as it moves away from the optical axis in the direction corresponding to the main scanning, and reaches the maximum value, and then monotonically and smoothly. Decrease to. Therefore, the "variation" of the radius of curvature in the plane orthogonal to the deflection at each incident position
Is effectively reduced, and the tolerance for the disposition tolerance of the optical scanning lens in the main scanning corresponding direction is increased.

When there is a position error in the main scanning direction: ΔY at the radius of curvature: r (Y), the error in the radius of curvature at the position: Y is {dr (Y) / dY} ΔY, and r (Y) is Y. In the case of a monotonic increase with an increase of, since {dr (Y) / dY} always has a constant sign, {dr (Y) / dY} ΔY may be remarkably large. If r (Y) has a maximum, the sign of {dr (Y) / dY} changes before and after the maximum, so that {dr (Y) / dY} ΔY is effectively small.

FIG. 5 (a) shows the field curvature in the main scanning direction in Example 1 with the f.theta. Characteristic and linearity as constant velocity characteristics shown in (b).

As shown in FIG. 5A, in the first embodiment, the "field curvature in the main scanning direction" is satisfactorily corrected. This is mainly because the "surface shape within the deflecting surface" of the first to fourth surfaces is appropriately determined. In addition, as can be seen from the above list, the "field curvature in the sub-scanning direction" is extremely good at "0.1 mm or less" over the effective main scanning area.

In order to see the effect of the surface shape of the fourth surface,
The surface shape of the fourth surface is the radius of curvature in the deflection surface: R =-
Considering the arc of 500 as a "normal toroidal surface" obtained by rotating around an axis of rotation r (0) = -14.36 apart on the optical axis, the field curvature in the main and sub-scanning directions at this time Is as shown in FIG. Even in this state, the field curvature in the sub-scanning direction is corrected quite well.

As in the first embodiment, when the radius of curvature R (Y) in the plane orthogonal to the deflection of the fourth surface has a maximum while Y increases, a positive value in the sub-scanning corresponding direction on the fourth surface is obtained. The power gradually decreases from the optical axis as the image height increases, reaches a local minimum, and then gradually increases, so that the image forming position in the sub-scanning direction is displaced to the positive side of the field curvature at the maximum portion. This has an effect, whereby the field curvature in the sub-scanning direction shown in FIG. 5C is satisfactorily corrected.

Example 2 This is a specific example of the embodiment shown in FIG.

S = 234.7, S ₀ = 40, d ₁ = 13.
82, l ₁ = 8.58, d ₂ = 11.5, l ₂ = 100.
1, N ₁ = 1.537, N ₂ = 1.537.

First surface Surface shape: A concave shape obtained by rotating a shape in the deflection surface of a non-arcuate shape (shape specified by the formula (1)) around a rotation axis parallel to the main scanning corresponding direction. Barrel-shaped toroidal shape (see FIG. 2) Shape in deflection plane: X (Y) R = −310, K = 27.65, A = −1.24849
E-6, B = 5.484729E-10, C = -7.0
2444E-13, D = 3.7688E-16 F = 7.8538E-20, G = -4.3694E-
23, I = -2.755E-26, J = 7.47E-
30 F, G, I and J are Y's 12, 14, 16 and 1, respectively.
It is a higher-order coefficient of the 8th power term. Radius of curvature in the plane orthogonal to the deflection on the optical axis: r (0) (Fig. 2
Curve: distance between X (0) and axis of rotation AX) r (0) =-19.5
.

Second surface Surface shape: Normal toroidal surface Curvature radius in deflection plane: R = -87.5 Curvature radius in deflection orthogonal plane on optical axis: r (0) (FIG. 2)
Reference) r (0) =-31.0
.

Third surface: surface on the optical deflector side of the optical scanning lens Surface shape: concave barrel-shaped toroidal surface whose deflection surface has a non-arcuate shape (see FIG. 2) Deflection surface shape: X ( Y) R = -246, K = -15.44, A = 7.6366
E-7, B = -6.71852E-11, C = -5.3
1168E-15, D = -9.743133E-19, F
= -1.276E-23, G = -3.519E-25,
I = 2.322E-28, J = -3.167E-32 F, G, I, and J are 12, 14, 16, and 1 of Y, respectively.
It is a higher-order coefficient of the 8th power term. Radius of curvature in the plane orthogonal to the deflection on the optical axis: r (0) (Fig. 2
Curve: distance between X (0) and rotation axis AX) r (0) =-121.25
.

Fourth surface: surface on the scanned surface side of the optical scanning lens Surface shape: surface shape described with reference to FIG. 3 Shape in deflecting surface: X (Y) (arc shape) Curvature radius: R = 248.3 Radius of curvature in the plane orthogonal to the deflection: r (Y) Radius of curvature in the plane orthogonal to the deflection with respect to the incident position: Y of the principal ray of the deflected light beam on the fourth surface in the main scanning corresponding direction (Y direction). : R (Y) at a typical incident position: Y = −55.
4, -47.8, -35.3, -20.2, -0.1,
When the image height: H and the curvature of field in the sub-scanning direction (unit: mm) are set at each image height corresponding to the respective values of 20.2, 35.3, 47.8, and 55.4 (mm). Correspondence is shown in the list.

Incident position: Y -55.42 -47.8 -35.3 -20.2 -0.1 Radius of curvature: r (Y) -19.11 -19.36 -19.63 -19.54 -19.45 Image height: H -109.1 -97.0 -74.5 -43.5 0.0 Image plane Curvature: 1.23 0.19 0.77 0.19 1.23.

Incident position: Y 20.2 35.3 47.8 55.4 Radius of curvature: r (Y) -19.54 -19.63 -19.36 -19.11 Image height: H 43.5 73.1 94.2 105.6 Field curvature: -0.76 0.33 -0.28 0.16.

The radius of curvature of the fourth surface in the plane orthogonal to the deflection increases monotonically and smoothly while reaching the maximum value as the optical axis moves away in the main scanning corresponding direction, and then monotonically and smoothly decreases. Therefore, the "variation" of the radius of curvature in the plane orthogonal to the deflection at each incident position is effectively reduced, and the tolerance for the arrangement tolerance of the optical scanning lens in the main scanning corresponding direction is increased.

FIG. 6 (a) shows the field curvature in the main scanning direction in Example 1 with the fθ characteristic as a constant velocity characteristic and linearity being shown in (b). The field curvature in the main scanning direction is well corrected, and the field curvature in the sub scanning direction is also extremely good (1.3 mm or less) as shown in the above list.

In the embodiment shown in FIG. 4, sag is generated by the optical deflector, and the field curvature in the sub-scanning direction is asymmetric with respect to the optical axis. The polygon mirror, which is an optical deflector, has six deflective reflection surfaces, and the radius of the inscribed circle is 18 mm.

In the second embodiment, in order to eliminate the influence of sag, the optical scanning lens is shifted by "0.1 mm" in the negative direction of the Y direction which is the main scanning corresponding direction. By this shift, the asymmetry of the field curvature in the sub-scanning direction due to the influence of the sag is effectively improved as seen in the above list. In order to improve the influence of the sag, it is also effective to give the optical scanning lens a "tilt" in the deflection plane.

In both the first and second embodiments, the constant velocity characteristic (f.theta. Characteristic) is good as described above, and the field curvature in the main and sub-scanning directions is well corrected. Is small, and good optical scanning is possible.

In the first and second embodiments, the light flux incident on the scanning and imaging lens is not a parallel light flux in the main scanning corresponding direction, so the fθ characteristic as a constant velocity characteristic is not strictly accurate, but fθ is weak because of its poor convergence. It is possible to express the constant velocity characteristic sufficiently accurately with the characteristic.

[0084]

As described above, according to the present invention, it is possible to provide an optical scanning lens / scanning imaging lens and an optical scanning device.

According to the present invention, in the optical scanning device and the scanning imaging lens, it is possible to effectively alleviate the tolerance for the assembling tolerance to the optical scanning device while keeping the conjugating function and the constant velocity function satisfactorily. to enable.

As described above, the optical scanning lens can be easily manufactured by molding a resin such as plastic.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining one embodiment of an optical scanning device of the present invention.

FIG. 2 is a diagram for explaining a barrel-shaped toroidal surface.

FIG. 3 is a diagram for explaining a surface shape of a scanning surface side of an optical scanning lens.

FIG. 4 is a diagram for explaining another embodiment of the optical scanning device of the present invention.

5A and 5B are diagrams of field curvature and constant velocity characteristics related to Example 1. FIG.

6A and 6B are diagrams of field curvature and constant velocity characteristics according to the second embodiment.

[Explanation of symbols]

 1 LD 2 Coupling Lens 3 Cylinder Lens 5 Deflection / Reflection Surface 6 Lens 7 Optical Scanning Lens 8 Scanned Surface

Claims (7)

[Claims] 1. A deflected light beam is scanned by deflecting a light beam imaged in a long line image in a direction corresponding to main scanning at an equal angular velocity by an optical deflector having a deflective reflection surface near the image formation position of the line image. In an optical scanning device that converges a light spot on a surface to be scanned by an imaging lens to perform uniform optical scanning of the surface to be scanned, a part of a scanning imaging lens composed of a plurality of lenses is used. The lens is a meniscus lens having a concave surface facing the optical deflector side, and the surface on the optical deflector side is a concave barrel-shaped toroidal surface having a rotation axis parallel to the main scanning corresponding direction. On the scanning surface side, the absolute value of the radius of curvature in the plane orthogonal to the deflection increases smoothly and monotonically toward the maximum value as it leaves the optical axis in the main scanning corresponding direction, and after exceeding the maximum position, the optical axis Decreases smoothly and monotonically And the line connecting the centers of curvature in the plane orthogonal to the deflection of the surface on the side to be scanned is defined as a curve along the main scanning corresponding direction in the deflection surface. Scanning lens. 2. The optical scanning lens according to claim 1, wherein the optical scanning lens is arranged closest to a surface to be scanned among a plurality of lenses forming a scanning imaging lens. . 3. The optical scanning lens according to claim 2, wherein the surface on the optical deflector side is a barrel-shaped toroidal surface having a non-arcuate shape in the deflecting surface, and the surface on the scanned surface side is An optical scanning lens characterized in that the shape in the deflecting surface is an arc shape. 4. A light beam imaged in a long line image in the main scanning corresponding direction is deflected at an equal angular velocity by an optical deflector having a deflective reflection surface near the image formation position of the line image, and the deflected light beam is scanned. In the optical scanning device for converging a light spot on the surface to be scanned by the imaging lens as a light spot and performing uniform optical scanning of the surface to be scanned, a scanning imaging lens composed of a plurality of lenses, It is composed of two lenses, one of the two lenses is the optical scanning lens according to claim 3, and the lens on the optical deflector side has a coaxial aspherical surface on the optical deflector side. A scanning imaging lens having a spherical surface on the surface to be scanned. 5. A light beam focused into a long line image in the main scanning direction is deflected at a constant angular velocity by an optical deflector having a deflective reflection surface near the image forming position of the line image, and the deflected light beam is scanned. In a light scanning device for converging light as a light spot on a surface to be scanned by an imaging lens to perform uniform optical scanning of the surface to be scanned, a scanning imaging lens composed of a plurality of lenses, It is composed of two lenses, and one of the two lenses is the optical scanning lens according to claim 3, and the lens on the optical deflector side has the surface on the optical deflector side within the deflecting surface. The shape is a non-circular shape,
A scanning imaging lens characterized in that it has a barrel-shaped toroidal surface having a rotation axis parallel to the main scanning direction, and the surface to be scanned is a normal toroidal surface. 6. A deflected light beam is scanned by deflecting a light beam imaged in a long line image in the main scanning corresponding direction at an equal angular velocity by an optical deflector having a deflective reflection surface near the image formation position of the line image. In a light scanning device for converging a light spot on a surface to be scanned as a light spot by the image forming lens to perform uniform optical scanning of the surface to be scanned, a scanning image forming lens composed of a plurality of lenses is provided. An optical scanning device comprising the optical scanning lens described in 1 or 2 or 3. 7. A deflected light beam is scanned by deflecting a light beam imaged in a long line image in the main scanning corresponding direction at an equal angular velocity by an optical deflector having a deflective reflection surface near the image formation position of the line image. An optical scanning device for converging a light spot on a surface to be scanned by an imaging lens to perform a uniform optical scanning of the surface to be scanned, wherein the scanning imaging lens is a scanning imaging device according to claim 4 or 5. An optical scanning device characterized by being a lens.