JP3421704B2 - Scanning imaging lens and optical scanning device - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A direction corresponding to a main scanning direction (a direction corresponding to a main scanning direction on a virtual optical path in which an optical path extending from a light source to a surface to be scanned is linearly developed along an optical axis of an optical system say,
A light beam formed into a long line image in a direction parallel to the sub-scanning direction on the virtual optical path in the sub-scanning corresponding direction) has a deflective reflection surface near the image forming position of the line image. Conventionally, an optical scanning device that deflects light at a constant angular velocity by an optical deflector, condenses it as a light spot on a surface to be scanned by a scanning imaging lens, and optically scans the surface to be scanned at a uniform speed has been conventionally used in optical printers and digital copying machines. It is widely known in connection with devices.

In such an optical scanning device, it has been proposed to use a "single-lens configuration" scanning imaging lens from the viewpoints of downsizing the device and reducing the price (Japanese Patent Laid-Open No. 7-1).
74998, etc.).

It is desirable that the optical scanning device be "compact and have a wide effective scanning area". For this reason, in order to make the range of the effective deflection angle by the optical deflector large and to prevent the size of the scanning imaging lens from increasing. It is necessary to arrange the scanning imaging lens as close to the optical deflector as possible.

When the scanning image-forming lens having a single-lens structure is arranged close to the optical deflector in this way, the magnification of the scanning image-forming lens in the sub-scanning corresponding direction increases, and for example, an optical image for forming the above-mentioned line image is formed. Even if the image forming position of the line image slightly shifts on the virtual optical path due to a slight positional error in the optical axis direction of the system, the image forming position of the light spot in the sub-scanning corresponding direction largely shifts. The field curvature becomes much worse than designed.

Also, in the case of a single-lens scanning imaging lens, the curvature of field in the sub-scanning direction is changed so that the light spot diameter, particularly the light spot diameter in the sub-scanning direction does not change depending on the image height of the light spot. It is desirable that the correction be performed as well as possible.

Even if the curvature of field in the sub-scanning direction is well corrected, if a scanning image forming lens disclosed in Japanese Patent Laid-Open No. 4-50908 is used, a line image near the deflecting reflection surface and a line image near the image surface are obtained. Since the lateral magnification in the sub-scanning corresponding direction between the imaging points in the sub-scanning corresponding direction changes depending on the image height, the light spot diameter in the sub-scanning direction changes depending on the image height.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention aims to alleviate the restriction on the assembly tolerance of the optical element in the optical axis direction in the optical scanning device using the single-lens scanning imaging lens. It is an issue.

Another object of the present invention is to satisfactorily correct the constant velocity characteristics of optical scanning and the field curvature in the sub-scanning direction in a single-lens scanning imaging lens.

Another object of the present invention is to reduce the deviation of the light spot diameter due to the image height of the light spot in a single-lens scanning imaging lens.

[0011]

The scanning image forming lens of the present invention is an optical deflector having a deflecting / reflecting surface in the vicinity of an image forming position of a line image of a light beam formed into a long line image in the main scanning corresponding direction. Is a scanning imaging lens in an optical scanning device that deflects light at a constant angular velocity with a scanning imaging lens to condense it as a light spot on the surface to be scanned, and scans the surface to be scanned at a constant speed. It has the following characteristics (claim 1).

That is, the scanning and imaging lens of the present invention has a "single-lens configuration", and at least one surface thereof has a "non-arcuate shape" as a "shape in the deflecting surface".

The "deflecting surface" is a plane on which the principal ray of the deflected light beam ideally deflected by the optical deflector is swept. As described above, the main scanning corresponding direction and the sub scanning corresponding direction are orthogonal to the optical axis of the scanning imaging lens (since the virtual optical path matches the optical axis of the scanning imaging lens). Therefore, it can be said that the deflection surface is "a plane including the main scanning direction and the optical axis of the scanning imaging lens".

The "non-arcuate shape" means that the coordinate in the optical axis direction is X,
The coordinate in the direction orthogonal to the optical axis is Y, the paraxial radius of curvature is R, the conical constant is K, and the higher-order coefficients are A, B, C, D. ． ． As 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. ． ． Is a curve shape specified by.

Since this shape is the shape in the deflecting surface as described above, the above-mentioned coordinate: Y is the coordinate in the main scanning corresponding direction. Therefore, this non-arc shape is the surface of the scanning imaging lens having a single-lens structure. Can also be referred to as “the shape in the main scanning corresponding direction”.

At least one of the two surfaces of the scanning imaging lens is a "special toric surface".

In the present specification, the "special toric surface" means that the "line connecting the centers of curvature in the plane orthogonal to the deflection" of the lens surface at each position of the curve that specifies the surface shape in the deflection surface is the deflection. It is defined as a surface that draws a curve different from the above curve (surface shape in the deflection surface) in the surface.

The "deflection orthogonal plane" is a plane which is parallel to the optical axis of the scanning imaging lens among the planes orthogonal to the deflection plane. Therefore, the orthogonal plane of deflection is parallel to the sub-scanning corresponding direction, and its position can be specified by the coordinate: Y.

The scanning image forming lens of the present invention further has the following features.

That is, the "shape in the plane orthogonal to the deflection including the optical axis" is a meniscus shape with a concave surface facing the optical deflector side. The deflection orthogonal plane including the optical axis is a deflection orthogonal plane at Y = 0, and is a plane including the optical axis and the sub-scanning corresponding direction.

According to a first aspect of the present invention, there is provided a scanning image forming lens, wherein
In the inspection imaging lens, the main scanning corresponding direction of the incident position on the surface of the optical deflector side and the exit position of the principal ray of the deflected light beam incident on the scanning imaging lens at the deflection angle: θ from the surface on the scanned surface side. , Y ′, the distance from the image forming position of the line image to the incident position is S (θ), the distance between the incident position and the exit position is d (θ), and the distance from the exit position is The distance to the image forming point in the sub scanning corresponding direction is l (θ), and the effective paraxial radii of curvature in the orthogonal deflection planes at the incident position and the exit position are r _s1 '(Y) and r _s2 ' ( Y ′), where n is the refractive index of the lens material with respect to the wavelength used, P (θ) = d (θ) / [n {r _s2 '(Y ′) − r _s1 ′ (Y)} + (n− 1) · d (θ)] | β (θ) | = {l (θ) + _rs2 '(Y') · P (θ)} / {S (θ) _-rs1 '(Y) P (θ) }, | Β (0) | is a condition: (1) 1.45 ≦ | β (0) | ≦ The above-mentioned r _s1 '(0) and r _s2 ' (0) are set so as to satisfy 4.75.

The "orthogonal deflection plane" is a plane which includes a principal ray of a deflected light beam deflected at a deflection angle of θ and includes the principal ray and is orthogonal to the "deflection plane". Bend according to.

Of the above two paraxial radii of curvature, r _s1 '
(Y) is a paraxial radius of curvature in the orthogonal deflection plane with respect to the principal ray of the deflected light beam incident on the lens surface on the optical deflector side.

The paraxial radius of curvature: r _s2 '(Y') is in the orthogonal deflection plane with respect to the principal ray of the "deflected light flux in the lens" incident toward the position Y'of the lens surface on the scanned surface side. It is in.

As described above, the lens surface in the plane orthogonal to the deflection is circular, and the radius of curvature thereof is uniquely determined depending on the position: Y, Y '. Therefore, the lens surface shape at the positions: Y and Y ′ is apparently “elliptical”, and its curvature is represented by the paraxial radius of curvature. Therefore, the deflection angle: θ is 0
, I.e., Y = Y '= 0, r _s1 ' (0),
r _s2 '(0) is the radius of curvature in the plane orthogonal to the deflection including the optical axis: r
_{It is equal to s1} (0) and r _s2 (0), respectively.

According to a second aspect of the present invention, there is provided a scanning and image forming lens , wherein the light beam formed into a long line image in the main scanning corresponding direction is formed into the line.
An optical deflector having a deflecting / reflecting surface near the image forming position is used.
Deflection at a constant angular velocity and scanned by the scanning imaging lens
Condensed as a light spot on the surface to scan the surface to be scanned at a constant speed.
Scan imaging lens in an optical scanning device that optically scans
Therefore, it has a single-lens configuration, the coordinate in the optical axis direction is X, and the optical axis is orthogonal.
Direction coordinate Y, paraxial radius of curvature R, cone constant K, high
Let the following coefficients be A, B, C, D. ． ． ^{As, 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. ． ． Give
The non-circular shape specified by
Having as a shape in the facing surface, of at least one surface
The line obtained by connecting the centers of curvature in the plane orthogonal to the deflection is
In the deflection plane, a curve different from the shape of the above-mentioned one plane
, The shape of one surface is a special toric.
Shape defined in the plane and within the orthogonal plane of deflection including the optical axis
However, it has a meniscus shape with the concave surface facing the optical deflector side. "
In the scanning imaging lens, when | β (θ) | is within the effective scanning area, the condition: (2) 0.95 | β (0) | ≦ | β (θ) | ≦ 1.05 | β (0) It is characterized in that r _s1 '(Y) and r _s2 ' (Y ') are set so as to satisfy |.

There are various "combinations of the shapes of the respective surfaces" of the single-lens scanning imaging lens of the present invention. For example, as shown in the embodiments described later, "the surface on the side of the optical deflector is a non-arc shape". The shape is a non-circular toric surface obtained by rotating around the axis parallel to the main scanning direction in the deflection surface, and the surface on the scanned surface side is a special toric with the shape in the deflection surface being a non-circular shape. may be a surface with "," a surface of the optical deflector side and the non-arcuate toric surface obtained a non-arcuate shape to rotate around an axis parallel to the main scanning corresponding direction within the deflection surface, to be scanned the surface of the side, the shape of the deflecting surface as a special toric surface of an arc shape "to be rather good, is Raniwa" surface and the surface of the scanned surface side of the optical deflector side are both deflected It is a special toric surface whose in-plane shape is a non-circular shape. "
Yes.

The "shape in the deflection plane" of the single-lens scanning imaging lens of the present invention is optimized in order to improve the field curvature in the main scanning direction and the constant velocity characteristic.

The optical scanning device according to the present invention "deflects a light beam formed into a long line image in the main scanning corresponding direction at an equal angular velocity by an optical deflector having a deflection reflection surface near the image forming position of the line image. 3. An optical scanning device for condensing a light spot on a surface to be scanned by a scanning and imaging lens to scan the surface to be scanned at a constant speed.
It is characterized by using the scanning imaging lens described in ( 3 ).

As the "optical deflector", a rotating single-sided mirror such as a tenon mirror, a rotating double-sided mirror, or a polygon mirror can be used.

The light beam incident on the deflecting / reflecting surface of the optical deflector has a converging property in the sub-scanning corresponding direction, and due to the converging property, a long line image is formed in the main scanning corresponding direction. Can be convergent or divergent or parallel ”. If the light beam incident on the deflecting / reflecting surface is parallel to the main scanning corresponding direction, the scanning imaging lens is a single-lens fθ lens.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments will be described below.

In FIG. 1, reference numeral 0 is a light emitting source LD,
Reference numeral 12 indicates a coupling lens that constitutes a “light source” together with the LD 10. The divergent light beam emitted from the LD 10 is coupled by the coupling 12, is condensed in the sub-scanning corresponding direction (direction orthogonal to the drawing) by the cylinder lens 14 which is a line image forming optical system, and is reflected by the optical deflector. It is focused on the position of the deflective reflection surface 16 as a long line image in the main scanning corresponding direction.

In this embodiment, the optical deflector is assumed to be a "rotary single-sided mirror", the rotation axis 16A of the deflection reflection surface 16 is inside the deflection reflection surface 16, and the line image is formed at the position of the rotation axis 16A. Image. In this embodiment, a deviation between the line image and the deflecting / reflecting surface, that is, so-called “sag”, which is caused by rotation of the deflecting / reflecting surface 16, does not occur.

The cylinder lens 14 may be replaced by a concave cylinder mirror.

When the deflecting / reflecting surface 16 rotates at a constant angular velocity, the reflected light beam is also deflected at a constant angular velocity to become a deflected light beam, which is incident on the scanning / imaging lens 18 having a single-lens structure, and the scanning / imaging lens 1 is formed.
By the image forming action of 8, the light spot is condensed as a light spot on the scan surface 20 and the scan surface 20 is scanned at a constant speed.

A photoconductive photosensitive member is usually provided at the position of the surface 20 to be scanned, and writing is performed by optical scanning with the light spot.

For the scanning and imaging lens 18 having a single-lens configuration, the shape in the "deflection surface" (the shape shown in the figure) is
The surface on the optical deflector side is represented by X ₁ (Y), and the surface on the scanned surface side is represented by X ₂ (Y). Y is a coordinate in the main scanning corresponding direction with the optical axis AX position as the origin.

The surface shape in the sub-scanning corresponding direction is r _s1 (Y) on the surface on the optical deflector side and r r on the surface on the scanned surface side.
It is represented by _s2 (Y). r _s1 (Y) is the “radius of curvature of the surface on the optical deflector side in the plane orthogonal to the deflection” at the coordinate: Y, and r _s2
(Y) is the "radius of curvature of the surface on the optical deflector side in the plane orthogonal to the deflection" at the coordinate Y.

As shown in FIG. 1B, the "cross-sectional shape of the scanning image forming lens 18 taken along the plane orthogonal to the deflection including the optical axis AX" is a meniscus whose concave surface faces the optical deflector side (left side in the figure). The shape. By adopting such a meniscus shape, both the front main surface: H and the rear main surface: H'can be moved to the surface to be scanned side, and while the scanning imaging lens is positioned on the optical deflector side, The image forming magnification of the spot in the sub-scanning corresponding direction can be reduced.

The "non-circular toric surface" and the "special toric surface" will be described below. A toric surface is defined as a curved surface shape drawn by an arc when the arc is rotated about a straight line that is in the same plane as the arc and does not pass through the center of the arc.

The "non-arcuate toric surface" is a surface shape obtained by rotating a non-arcuate shape about a straight line in the same plane as this non-arcuate shape. FIG. 2A shows an example of a non-circular toric surface.

In FIG. 2A, X (Y) is a "non-arcuate shape", and its paraxial radius of curvature: R and conic constant:
K, higher order coefficients: A, B, C, D. ． ． And so on, X = Y ² / [R + R · √ {1- (1 + K) Y ² / R ² }] +
A · Y ⁴ + B · Y ⁶ + C · Y ⁸ + D · Y ¹⁰ +. ． ． It is expressed by the formula.

The non-arcuate toric surface of FIG. 2A is obtained by rotating the above non-arcuate shape: X (Y) around a rotation axis ax parallel to the Y-axis. At this time, in the cross-section of the plane parallel to the XZ plane, the radius of curvature of the non-circular toric surface is r shown in the figure when the Y coordinate of the cross-section is Y = η.
(η).

On the non-circular toric surface, as shown in FIG. 2A, the center of curvature in the cross section of the plane parallel to the XZ plane always coincides with the rotation axis ax. That is, the line connecting the centers of curvature is the "rotation axis ax itself".

Two examples of "special toric surface" are shown in FIG.
Shown in (b) and (c). 2 (b) and (c),
X (Y) represents a curve in the XY plane. In the illustrated example, X (Y) has a non-arcuate shape, but may have a simple arc shape or a straight line parallel to the Y axis.

In the special toric surface, at each point of the curve: X (Y), the radius of curvature in the plane parallel to the XZ plane is determined as a function of the coordinate: Y, and the center of curvature at each Y coordinate position is in the XY plane. And the curve connecting the centers of curvature:
L (Y) is also in the XY plane, and the curve: L (Y) is X
The curved surface has a shape different from that of (Y).

The special toric surface shown in FIG. 2 (b) is
When the curve: L (Y) is on the side opposite to the paraxial curvature center (paraxial radius of curvature: R) of the curve: X (Y), the special toric surface shown in (c) is the curve: L (Y ) Is on the same side as the paraxial curvature center of the curve: X (Y) (paraxial curvature radius: R).

According to the present invention, by appropriately setting the lens surface shapes: X ₁ (Y) and X ₂ (Y) in the deflection surface,
The shape in the main scanning corresponding direction, which is set in this way, by properly correcting the field curvature and the constant velocity characteristic in the main scanning direction: X
By determining r _s1 (Y), r _s2 (Y) depending on ₁ (Y), X ₂ (Y), ie, "correlate with X ₁ (Y), X ₂ (Y)", The field curvature in the sub-scanning direction and the constant velocity characteristic are well corrected.

Referring to FIG. 3A, this figure shows the state of the principal ray of the deflected light beam deflected at the deflection angle: θ at the position of the rotation axis 16A of the deflection reflection surface 16 (the starting point of deflection). There is.

A light ray portion ln1 on the incident side of the principal ray of the deflected light beam incident on the scanning imaging lens 18 at a deflection angle: θ is incident on the surface on the optical deflector side at an incident position Y in the main scanning corresponding direction and refracted. As a result, the light ray portion ln2 travels through the lens and exits from the surface on the scanned surface side at the position Y ′ in the main scanning corresponding direction,
The light beam portion ln3 is incident on the surface 20 to be scanned.

S (θ), d (θ), l in claims 1 and 2
(θ), r _s1 '(Y), and r _s2 ' (Y ') will be described with reference to FIG.
6A position) to the incident position, that is, the ray portion l
The length of n1 is S (θ), the distance between the incident position and the exit position, that is, the length of the light ray part ln2 in the lens 18 is d.
(θ), the distance from the exit position to the image forming point in the sub-scanning corresponding direction, that is, the length of the light ray portion ln3 is l (θ).

Also, the light ray parts ln1, ln2, of the chief ray
A plane including ln3 and orthogonal to the drawing is an “orthogonal deflection plane”, but in the orthogonal deflection plane including the light ray portion ln1, the effective paraxial radius of curvature of the lens surface at the position Y is r _s1 ′.
(Y), and the effective paraxial radius of curvature of the lens surface at the position Y ′ is r _s2 ′ (Y ′) in the orthogonal deflection plane including the light ray part ln2.

Therefore, when the deflection angle θ is 0, the above Y
= Y ', and in this case, S (0), d (0), and l (0) are as shown in FIG.

FIG. 3B shows the cross-sectional shape of the scanning and imaging lens 18 in the "deflection orthogonal plane including the optical axis".

In the figure, symbol A indicates the "origin of deflection" of the principal ray by the deflective reflecting surface, and symbol B indicates the "imaging position (in the sub-scanning direction)" of the light spot. Reference signs H and H'represent the front and rear principal surfaces on the optical axis in the sub-scanning corresponding direction, respectively. ΔH is the amount of deviation between the surface on the optical deflector side and the front main surface: H
Letting (0) be ΔH ′ (0) the deviation amount between the lens surface on the scanned surface side and the rear main surface: H ′, these are expressed as follows using the symbols in the figure.

That is, ΔH (0) = − r _s1 ′ (0) × d (0) / [n {r _s2 ′ (0) −r _s1 ′ (0)} + (n−1) · d (0 )] = − R _s1 ′ (0) × P (0) ΔH ′ (0) = − r _s2 ′ (0) × P (0). At this time, the absolute value of the lateral magnification of image formation in the sub-scanning corresponding direction: β (0) is | β (0) | = {l (0) −ΔH ′ (0)} / {S (0) + ΔH
(0)} = {l (0) + _rs2 '(Y') P (0)} / {S (0)-
r _s1 '(Y) P (0)}. As described above, r _s1 '(0) = r _s1 (0), r _s2 '
(0) = r _s2 (0).

Therefore, the meniscus shape (r _s2 (0) <
By setting 0, r _s1 (0) <0), both the front principal point and the rear principal point can be brought closer to the image side, that is, the scanned surface side, and the magnification in the sub-scanning corresponding direction | β (0) | Can be made smaller. At this time, the vertical magnification of the image formation is β ² (0).

In FIG. 1, for example, the cylinder lens 14
When the deployment position of is shifted by “Δ” in the optical axis direction, the image forming position of the light spot in the sub-scanning direction is a distance in the optical axis direction: Δ × β
² (0) shifts. Therefore, in order to increase the tolerance for the above position error: Δ, the absolute value of the lateral magnification: | β (0) |
Should be set as small as possible.

As a method of reducing | β (0) |, it is conceivable to bring the scanning and imaging lens 18 closer to the surface to be scanned. In this method, the thickness and effective diameter of the scanning and imaging lens (main scanning direction) are used. Of) tends to be large.

According to the first aspect of the present invention, the scanning / imaging lens is provided on the side of the optical deflector as much as possible, so that the scanning / imaging lens can be made compact, but the tolerance in the optical axis direction in assembling the optical element is strong. It is intended to realize an optical scanning device.

The condition (1) is a condition for achieving such an object.

When the lower limit of the condition (1) is exceeded, the thickness of the scanning imaging lens becomes large, and it becomes difficult to satisfactorily correct the field curvature in the sub-scanning direction and the constant velocity characteristic. If the upper limit is exceeded, the tolerance for the disposition tolerance in the main scanning direction becomes severe.

FIG. 3C shows the image formation state of the deflected light beam deflected at the deflection angle θ with respect to the principal ray. At this time, ΔH (θ) and ΔH ′ (θ) use the symbols in the figure, and ΔH (θ) = − r _s1 ′ (Y) × d (θ) / [n { _{rs 2} ′ (Y ′) −r _s1 ′ (Y)} + (n−1) · d (θ)] = − r _s1 ′ (Y) × P (θ) ΔH ′ (θ) = − r _s2 ′ (Y ′) × P ( θ), and the absolute value of the lateral magnification in the direction corresponding to the sub-scanning for a deflected light beam with a deflection angle of θ: | β (θ) | is | β (θ) |
+ R _s2 ′ (Y ′) · P (θ)} / {S (θ) −r _s1 ′ (Y) P (θ)}. Then, when the deflected light beam having the deflection angle: θ forms an image as a light spot at the point B, the light spot diameter in the sub-scanning direction: ω
₁ (θ) becomes ω ₁ = | β (θ) | · ω ₀ by using the light flux width in the sub-scanning corresponding direction of the line image formed at the origin of deflection: ω ₀ .

If the magnification: β (θ) varies greatly with the deflection angle: θ, the light spot diameter in the sub-scanning direction also varies greatly. "Tolerance of variation between image heights" of light spot diameter
Is usually within ± 5%.

In the invention described in claim 2 , | β (θ) | is within the effective scanning region under the condition: (2) 0.95 | β (0) | ≦ | β (θ) | ≦ 1.05 | β Satisfying (0) | is a condition for stabilizing the light spot diameter in the sub-scanning direction as described above. To satisfy this condition, r _s1 '(Y), r _s2 ' (Y ') Is set.

In the above description, it is assumed that the optical deflector does not cause “sag”. However, when a polygon mirror is used for the optical deflector, sag may occur and the curvature of field and constant velocity characteristics may be slightly deteriorated due to the sag, but this can be improved by shifting or tilting the scanning imaging lens. .

[0068]

EXAMPLES Specific examples will be described below.

Although not described above with reference to FIG. 1A, the light flux coupled by the coupling lens 12 may be a “parallel light flux” or a “weakly divergent light flux”. , Or “light flux with weak convergence”
It can also be

When the light beam coupled by the coupling lens 12 becomes a weakly convergent light beam, the deflection angle by the deflecting / reflecting surface 16: θ is set to 0, and the cylinder lens 1
4 and the scanning and imaging lens 18 are removed, the condensed light flux is condensed at a position indicated by a symbol Q in FIG. 1A (a position behind the scanned surface 20). This point Q is called a "natural light condensing point", and the distance from the starting point of the deflection by the deflection reflection surface 16 to the natural light condensing point Q is represented by S.

A sign is considered for S, and "when the natural condensing point Q is on the scanned surface side is positive" as shown in FIG. 1 (a).
When S is “negative”, the natural condensing point is on the light source side of the deflective reflection surface, and the light flux coupled at this time is weakly divergent. “S = ∞” when the coupled light flux is a parallel light flux.

In the following Examples 1 to 7, Examples 1 to 1
In No. 5, "no sag" is assumed as the optical deflector. Further, "n" represents the refractive index of the material of the scanning imaging lens at the used wavelength.

Higher-order coefficient: In the notation of A, B, C, and D, E and the numerical value following it indicate a power. For example, "E-
If it is " ⁹ ", this means "10 to ⁹ ", and this value is multiplied by the value immediately before it. The unit of the "quantity having the dimension of distance" is mm.

Example 1 S = -375.922 (the light beam coupled by the coupling lens 12 is a weakly divergent light beam) S (0) = 22.274 X ₁ (Y), r _s1 (Y ) D (0) = 10 n = 1.53664 X ₂ (Y), r _s2 (Y) l (0) = 142.927.

Surface on optical deflector side: Non-arc toric surface X ₁ (Y) (non-arc shape) R = 107.1, K = −60.197, A = −3.51
07E-6, B = 2.0684E-9, C = -8.9
722E-14, D = 1.1672E-17 r _s1 (Y) r _s1 (0) = -60.0
.

Surface to be scanned: Special toric surface X ₂ (Y) (non-arcuate shape) R = -119.999, K = 4.778039 A = -3.4156E-6, B = 1.5437E −
9, C = -1.8765E-12, D = 1.4637
E-15.

R _s2 (Y) is a value for deflection angle: θ: r
_A list of _s2 (Y ') is shown. θ (degrees) 0 10 20 30 36 36 40 45 Y'0 4.935 10.107 15.775 19.523 22.190 25.721 _s2 (Y ') -11.46 -11.56 -11.82 -12.08 -12.13 -12.06 -11.86.

R _s2 (Y ′) is polynomialized to r _s2 (Y ′) = a + b · Y ′ ² + c · Y ′ ⁴ + d · Y ′ ⁶ + e
Approximately Y ′ ⁸ + f · Y ′ ¹⁰ and determine the coefficients a, b, c, d, e, f by the method of least squares using Y ′ and the corresponding r _s2 (Y ′) numerical values. , A = -11.4579, b = -4.3509E-3, c
= 8.8457E-6, d = -6.9161E-9, e
= 5.3831E-12, f = -3.2985E-15
Became.

This approximation formula was used for the calculation of the aberration.

The condition (1) is satisfied with | β (0) | = 4.74.

When the power in the sub-scanning corresponding direction is applied to only one lens surface, | β (0) | becomes 4.97 or more, which does not satisfy the condition (1).

FIG. 4 shows the field curvature, constant velocity characteristic, and linearity of the first embodiment.

The "constant velocity characteristic" is the ideal image height when the deflection angle is θ: h (θ) (= constant × θ) and the actual image height: h '
It is defined as [{h '(θ) -h (θ)} / h (θ)] × 100 (%) using (θ).

In the field curvature diagram, the broken line represents the field curvature in the main scanning direction, and the solid line represents the field curvature in the sub scanning direction.

Example 2 S = −∞ (the light flux coupled by the coupling lens 12 is a parallel light flux) S (0) = 51.871 X ₁ (Y), r _s1 (Y) d (0) = 21.754 n = 1.53664 X ₂ (Y), r _s2 (Y) l (0) = 149.07.

Surface on optical deflector side: Non-circular toric surface X ₁ (Y) (non-circular shape) R = 461.302, K = 35.937, A = -2.
205E-7, B = 2.732E-11, C = -4.
9587E-15, D = 1.6048E-19 r _s1 (Y) r _s1 (0) = − 73.845
.

Surface to be scanned side: Special toric surface X ₂ (Y): The arc shape r _s2 (Y) of R = −97.244 has a value for deflection angle: θ: r _s2 (Y ′) Shown in a list. θ (degree) 0 6 14 26 26 32 36 41 Y'0 6.831 16.005 30.152 37.565 42.713 49.470 r _s2 (Y ') -20.64 -20.6 -20.42 -19.77 -19.18 -18.64 -17.75.

R _s2 (Y ′) = a + b · Y ′ ² + c · Y ′ ⁴ + d
Approximately Y ′ ⁶ + e · Y ′ ⁸ + f · Y ′ ¹⁰ to determine the coefficients a, b, c, d, e, and f by the least square method, a = −20.63952, b =
0.82661E-3, c = 0.13218E-6, d
= 0.209082E-10, e = -0.53157E
It became -14, f = -4.71E-19.

| Β (0) | = 2.09, which satisfies the condition (1).

FIG. 5 shows a field curvature diagram and a constant velocity characteristic / linearity diagram relating to the second embodiment. In the second embodiment, since the coupled light flux is a parallel light flux, the “constant” in the constant velocity characteristic is the focal length in the main scanning corresponding direction: fm, and the constant velocity characteristic is the normal fθ.
It is a characteristic.

As is clear from the above description, Example 1,
Scanning image forming lens and claim 2 the invention of claim 1, wherein
It is an embodiment of the optical scanning device of the invention of No. 3 .

The following Examples 3 to 5 are claimed in Claims 1 and 2.
It is an embodiment of the scanning imaging lens described above and the optical scanning device described in claim 3 .

Example 3 S = -375.922 (the light beam coupled by the coupling lens 12 is a weakly divergent light beam) S (0) = 22.274 X ₁ (Y), r _s1 (Y ) D (0) = 10 n = 1.53664 X ₂ (Y), r _s2 (Y) l (0) = 142.927.

Surface on optical deflector side: special toric surface X ₁ (Y) (non-arcuate shape) R = 107.1, K = −60.197, A = −3.51
07E-6, B = 2.0684E-9, C = -8.9
722E-14, D = 1.1672E-17 r _s1 (Y): Deflection angle: The values for θ are listed below. theta (degrees) 0 10 20 30 36 40 45 Y 0 3.940 8.207 13.200 16.757 19.451 23.281 r s1 (Y) -22.0 -25.07 -29.076 -40.588 -50.791 -65.907 -85.507.

Surface to be scanned side: Special toric surface X ₂ (Y) (non-arcuate shape) R = -119.999, K = 4.778039 A = -3.4156E-6, B = 1.5437E −
9, C = -1.8765E-12, D = 1.4637
E-15.

R _s2 (Y): Deflection angle: value for θ: r
_A list of _s2 (Y ') is shown. θ (degrees) 0 10 20 30 36 36 40 45 Y'0 4.935 10.107 15.775 19.523 22.190 25.721 r _s2 (Y ') -9.807 -10.12 -10.53 -11.32 -11.77 -12.22 -12.58.

R _s1 (Y) = a + b · Y ² + c · Y ⁴ + d · Y
Approximating as ⁶ + e · Y ⁸ + f · Y ¹⁰ + g · Y ¹² , the coefficient:
When a, b, c, d, e, f, and g are determined by the least square method, a = −22, b = −2.5751E−1, c =
0.449657E-2, d = -4.4466449E-
5, e = 1.9569944E-7, f = -3.87E-
10, g = 2.792783E-13.

R _s2 (Y ′) = a ′ + b ′ · Y ′ ² + c ′ · Y ′ <sup>4
+ D '· Y' 6 +</sup> e '· Y' 8 + f '· Y 10 + g' · Y '12 approximates the coefficient: a', b ', c ', d ', e', f ',
When g'is determined by the method of least squares, a '=-9.80.
7, b '=-1.662605E-2, c' = 1.87
0374E-4, d '=-1.27425E-6, e'
= 4.079722E-9, f '=-6.029437
It was E-12, g '= 3.3315003E-15.

S (θ), d (θ), l (θ), r _S1 '(Y), r
_S2 '(Y') is shown as a list.

[0100] θ 0 10 20 30 36 40 45 S (θ) 22.274 22.689 23.997 26.399 28.509 30.261 32.924 d (θ) 10 9.876 9.452 8.551 7.635 6.793 5.386 l (θ) 142.887 144.327 148.338 154.765 159.674 163.608 168.608 r S1 '(Y) -22 -24.732 -27.589 -36.35 -43.735 -55.259 -69.233 r _S2 '(Y') -9.807 -10.101 -10.495 -11.382 -12.042 -12.761 -13.572 These data are obtained from the formula of P (θ) in claim 3. Substituting it on the right side to calculate β (θ), | β (θ)
| And | β (θ) / β (0) | are as follows.

[0101]   θ (degrees) 0 10 20 30 36 40 45   Y 0 3.94 8.207 13.2 16.757 19.451 23.281   | β (θ) | 4.42 4.47 4.49 4.53 4.53 4.55 4.52 | β (θ) / β (0) | 1.0 1.01 1.02 1.03 1.03 1.03 1.02.

The condition (1) is satisfied with | β (0) | = 4.24.

| Β (θ) | is between | β (0) | and 1.03 | β (0) | and satisfies the condition (2).

FIG. 6 shows a field curvature diagram and a constant velocity characteristic / linearity diagram relating to the third embodiment. Since the shape of the scanning imaging lens in the deflection surface of the third embodiment is the same as that of the first embodiment, the diagrams of the field curvature in the main scanning direction and the constant velocity characteristics / linearity are the same as those of the first embodiment. Is.

Example 4 S = 554.6 (The light beam coupled by the coupling lens 12 is a light beam having a weak convergence) S (0) = 38.916 X ₁ (Y), r _s1 (Y) d (0) = 15 n = 1.53664 X ₂ (Y), r _s2 (Y) l (0) = 120.984.

Surface on optical deflector side: special toric surface X ₁ (Y) (non-arcuate shape) R = 168.191, K = −39.924, A = −3.
4224E-7, B = 2.2729E-13, C =
8.0209E-15, D = -8.7059E-19 r _s1 (Y): Deflection angle: The values for θ are listed below. θ (degrees) 0 10 20 30 36 36 40 45 Y 0 6.886 14.368 23.208 29.610 34.524 41.574 r _s1 (Y) -31.0 -33.14 -45.56 -70.28 -81.84 -102.13 -126.96.

Surface to be scanned: Special toric surface X ₂ (Y) (non-arcuate shape) R = -188.994, K = -4.83792, A =-
4.9817E-7, B = 7.7236E-12, C
= -1.6386E-14, D = 1.7827E-1
8.

R _s2 (Y): Deflection angle: value for θ: r _s2
(Y ') is shown as a list. θ (degree) 0 10 20 30 36 36 40 45 Y'0 8.348 17.093 26.710 33.136 37.760 43.915 r _s2 (Y ') -13.91 -14.16 -15.25 -16.63 -16.99 -17.44 -17.54.

R _s1 (Y) = a + b · Y ² + c · Y ⁴ + d · Y
^By approximating ⁶ + e · Y ⁸ + f · Y ¹⁰ + g · Y ¹² and determining the coefficients: a, b, c, d, e, f, g by the method of least squares, a = −31, b = −3 .26
507E-2, c = -2.90654E-4, d = 5.
99426E-7, e = -3.997959E-10,
f = 4.109081E-14, g = 2.443981
It became E-17.

R _s2 (Y ′) = a ′ + b ′ · Y ′ ² + c ′ · Y ′ <sup>4
+ D '· Y' 6 +</sup> e '· Y' 8 + f '· Y' 10 + g · Y '12 approximates the coefficient: a', b ', c ', d ', e',
When f ′ and g ′ are determined by the method of least squares, a ′ = − 1
3.91, b '=-2.866184E-3, c' =-
1.21239E-5, d '= 2.690094E-
8, e '=-2.090761E-11, f' = 6.6
68513E-15, g '=-6.734702E-1
It became 9.

S (θ), d (θ), l (θ), r _S1 '(Y), r
_S2 '(Y') is shown as a list.

Θ 0 10 20 30 30 36 40 45 45 S (θ) 38.916 39.656 42.01 46.417 50.376 53.81 58.794 d (θ) 15 14.747 13.884 12.038 10.135 8.354 5.324 l (θ) 121.012 122.213 125.713 131.319 135.629 138.898 143.746 r _S1 '( -31 -32.676 -43.121 -62.437 -69.544 -84.248 -101.250 r _S2 '(Y') -13.91 -14.145 -15.21 -16.769 -17.478 -18.376 -19.395 These data are obtained from the formula of P (θ) in claim 3. Substituting in the right side and calculating β (θ) | β (θ) |
And | β (θ) / β (0) | are as follows.

[0113]   θ (degrees) 0 10 20 30 36 40 45   Y 0 6.886 14.368 23.208 29.610 34.524 41.573   | β (θ) | 2.19 2.20 2.25 2.29 2.28 2.27 2.27 | β (θ) / β (0) | 1.0 1.01 1.03 1.04 1.04 1.04 1.04.

The condition (1) is satisfied with | β (0) | = 4.24.

Also, | β (θ) | is | β (0) | and 1.04 | β
It is between (0) | and satisfies the condition (2).

FIG. 7 shows the field curvature, constant velocity characteristic, and linearity of the fourth embodiment.

Example 5 S = 316.7 (the light flux coupled by the coupling lens 12 is a weakly convergent light flux) S (0) = 48.618 X ₁ (Y), r _s1 (Y) d (0) = 20.0 n = 1.53664 X ₂ (Y), r _s2 (Y) l (0) = 106.282.

Surface on the optical deflector side: special toric surface X ₁ (Y) (non-arcuate shape) R = 200.224, K = -30.5827, A =-
1.5926E-7, B = -4.0453E-12, C
= 6.0017E-15, D = -3.9857E-1
9 r _s1 (Y): Deflection angle: A list of values for θ is shown. theta (degrees) 0 10 20 30 36 40 45 Y 0 8.605 17.967 29.208 37.180 43.459 52.640 r s1 (Y) -30.0 -29.18 -28.76 -27.74 -26.56 -24.18 -17.02.

Surface to be scanned: Special toric surface X ₂ (Y) (non-arcuate shape) R = -224.092, K = 1.199001, A =-
3.2013E-7, B = 7.0634E-12, C
= -9.2418E-15, D = 1.9593E-1
8.

R _s2 (Y): Deflection angle: value for θ: r _s2
(Y ') is shown as a list. θ (degree) 0 10 20 30 36 36 40 45 Y '0 10.583 21.558 33.647 41.714 47.523 55.334 r _s2 (Y') -15.32 -15.23 -15.12 -14.53 -13.64 -12.44 -9.34.

R _s1 (Y) = a + b · Y ² + c · Y ⁴ + d · Y
⁶ + e · Y ⁸ + f · Y ¹⁰ + g · Y ¹² and the coefficients a, b, c, d, e, f, and g are determined by the least square method, a = −30, b = 1. 521
146E-2, c = -6.399798E-5, d =
1.166608E-7, e = -9.651438E-
11, f = 3.652588E-14, g = -5.07
It became 3881E-18.

R _s2 (Y ′) = a ′ + b ′ · Y ′ ² + c ′ · Y ′ <sup>4
+ D '· Y' 6 +</sup> e '· Y' 8 + f '· Y 10 + g' · Y '12 approximates the coefficient: a', b ', c ', d ', e',
When f ′ and g ′ are determined by the method of least squares, a ′ = − 1
5.32, b '= 1.12584E-3, c' =-3.
490667E-6, d '= 5.91427E-9,
e '=-4.057836E-12, f' = 1.284
It became 796E-15, g '=-1.500234E-19.

S (θ), d (θ), l (θ), r _S1 '(Y), r
_S2 '(Y') is shown as a list.

Θ 0 10 20 30 30 36 40 45 S (θ) 48.618 49.552 52.533 58.152 63.255 67.611 74.444 d (θ) 20 19.662 18.494 15.956 13.296 10.774 6.411 l (θ) 106.282 107.376 110.608 115.846 119.932 123.124 127.823 r _S1 '( -30.0 -28.769 -27.175 -24.561 -22.426 -19.745 -13.291 r _S2 '(Y') -15.316 -15.220 -15.123 -14.736 -14.155 -13.233 -10.366 These data are expressed by the formula P (θ) in claim 3. Substituting in the right side and calculating β (θ) | β (θ) |
And | β (θ) / β (0) | are as follows.

[0125]   θ (degrees) 0 10 20 30 36 40 45   Y 0 8.605 17.967 29.076 37.180 43.459 52.640   | β (θ) | 1.46 1.45 1.44 1.42 1.41 1.41 1.40 | β (θ) / β (0) | 1.0 0.99 0.99 0.97 0.97 0.97 0.96.

| Β (0) | = 1.46, which satisfies the condition (1).

Also, | β (θ) | is | β (0) | and 0.96 | β
It is between (0) | and satisfies the condition (2).

FIG. 8 shows the field curvature, constant velocity characteristic, and linearity of the fifth embodiment.

[0129]

As described above, according to the present invention, a novel scanning lens and optical scanning device can be realized.

According to the first aspect of the invention, in the optical scanning device using the scanning and imaging lens having the single-lens structure, it is possible to achieve the object of relaxing the restriction on the assembly tolerance of the optical element in the optical axis direction.

According to a first aspect of the present invention , in an optical scanning device using a scanning and imaging lens having a single-lens structure, the restriction on the assembly tolerance of the optical element in the optical axis direction is relaxed, and the main and sub scanning directions are set. The field curvature and constant velocity characteristics of can be improved.

According to a second aspect of the present invention, in an optical scanning device using a scanning / imaging lens having a single-lens structure, the restriction on the assembly tolerance of the optical element in the optical axis direction is relaxed, and the optical spot diameter in the sub-scanning direction is reduced. Fluctuations can be effectively reduced.

According to a third aspect of the present invention, in an optical scanning device using a single-lens structure scanning imaging lens, the restriction on the assembly tolerance of the optical element in the optical axis direction is relaxed, and the assembly is easy and the cost can be reduced. You can

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining a non-circular toric surface and a special toric surface.

FIG. 3 is a diagram for explaining conditional expressions (2) and (3).

FIG. 4 is a diagram of field curvature and constant velocity characteristics / linearity according to the first embodiment.

FIG. 5 is a diagram of field curvature and constant velocity characteristics / linearity according to the second embodiment.

FIG. 6 is a diagram of field curvature and constant velocity characteristics / linearity regarding Example 3;

FIG. 7 is a diagram of field curvature and constant velocity characteristics / linearity regarding Example 4;

FIG. 8 is a diagram of field curvature and constant velocity characteristics / linearity regarding Example 5;

[Explanation of symbols]

10 LD 12 coupling lens 14 cylinder lens 16 Deflection reflective surface 18 Scanning imaging lens 20 Scanned surface

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-5-241094 (JP, A) JP-A-6-265807 (JP, A) JP-A-7-174998 (JP, A) JP-A-4- 104213 (JP, A) JP 4-110820 (JP, A) JP 4-149405 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 13/00 G02B 26 /Ten

Claims (3)

(57) [Claims] 1. A scanning imaging lens, wherein a light beam imaged in a long line image in the main scanning corresponding direction is deflected at a constant angular velocity by an optical deflector having a deflection reflection surface near the image forming position of the line image. A scanning and imaging lens in an optical scanning device that converges a light spot on a surface to be scanned by a laser beam and scans the surface to be scanned at a constant speed, and has a single-lens configuration, and the coordinate in the optical axis direction is X. , Y is the coordinate in the direction orthogonal to the optical axis, R is the paraxial radius of curvature, K is the conic constant, and A, B, C are higher order coefficients.
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. ． ． Has a non-arcuate shape specified by giving at least one surface as a shape in the deflection surface, and a line obtained by connecting the centers of curvature in the deflection orthogonal surface of at least one surface in the deflection surface, The shape of the one surface is defined as a special toric surface so that a curve different from the shape of the one surface is drawn, and the shape in the plane orthogonal to the deflection including the optical axis is concave on the optical deflector side. and Ri meniscus shape der, deflection angle: the main beam deflected light beam incident on the scanning imaging lens at θ
Position of the line on the surface on the optical deflector side and on the surface to be scanned side
The coordinates in the main scanning corresponding direction of the exit position from the surface
Respective Y, Y ', from the image forming position of the line image to the incident position
The distance is S (θ), and the distance between the incident position and the exit position is
d (θ), image formation in the sub-scanning corresponding direction from the exit position
The distance to the point is l (θ)
Each effective paraxial radius of curvature in the orthogonal deflection plane in
R _s1 '(Y), r _s2 ' (Y '), lens for the wavelength used
When the refractive index of the material is n, P (θ) = d (θ) / [n { _rs2 '(Y')- _rs1 '(Y)} + (n-1) · d (θ)] | Β (θ) | = {l (θ) + _rs2 '(Y') · P (θ)} / {S (θ) _-rs1 '(Y) P (θ)} , | β (0) Is set to satisfy the condition: (1) 1.45 ≦ | β (0) | ≦ 4.75 , r _s1 '(0), r _s2 ' (0) are set.
Scanning and imaging lens characterized by 2. A light beam formed into a long line image in the main scanning direction.
Is a light having a deflecting and reflecting surface near the image forming position of the line image.
The deflector deflects it at a constant angular velocity to make it a scanning imaging lens.
Focus the light spot on the surface to be scanned and
Scanning image formation in an optical scanning device that optically scans the scanning surface at a constant speed
It is a lens, which has a single-lens configuration, where the coordinate in the optical axis direction is X, the coordinate in the optical axis orthogonal direction is Y, and the paraxial curve
R is the radius of curvature, K is the conic constant, and A, B, C
D. ． ． ^{As, 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. ． ． Give
The non-circular shape specified by
It has a shape in the facing surface, and the center of curvature in the plane orthogonal to the deflection of at least one surface is
The line obtained by connecting the lines is the above-mentioned one plane in the deflection plane.
The shape of the above-mentioned one surface so that it draws a curve different from the shape of
The shape is defined as a special toric surface, and the shape in the plane orthogonal to the deflection including the optical axis is on the optical deflector side.
It is a meniscus shape with a concave surface, and the main light of the deflected light beam that enters the scanning imaging lens at a deflection angle of θ.
Position of the line on the surface on the optical deflector side and on the surface to be scanned side
The coordinates in the main scanning corresponding direction of the exit position from the surface
Respective Y, Y ', from the image forming position of the line image to the incident position
The distance is S (θ), and the distance between the incident position and the exit position is
d (θ), image formation in the sub-scanning corresponding direction from the exit position
The distance to the point is l (θ)
Each effective paraxial radius of curvature in the orthogonal deflection plane in
R _s1 '(Y), r _s2 ' (Y '), lens material for the wavelength used
P (θ) = d (θ) / [n { _rs2 '(Y')- _rs1 '(Y)} + (n-1) · d (θ)] where n is the refractive index of the material | Β (θ) | = {l (θ) + _rs2 '(Y') P (θ)} / {S (θ) _-rs1 '(Y) P (θ)} within the effective scanning area , | β (θ) | condition: (2) 0.95 | β ( 0) | ≦ | β (θ) | ≦ 1.05 | β (0) | so as to satisfy the above r _s1 '( Y), r _s2 '(Y') is set
A scanning imaging lens characterized in that 3. A light beam formed into a long line image in the main scanning corresponding direction.
Is a light having a deflecting and reflecting surface near the image forming position of the line image.
The deflector deflects it at a constant angular velocity to make it a scanning imaging lens.
Focus the light spot on the surface to be scanned and
An optical scanning device for optically scanning the scanning surface at a constant velocity, wherein the scanning imaging lens according to claim 1 or 2 as a scanning imaging lens.
An optical scanning device characterized by using a lens.