JPH11258531A - Optical scanner and scanning image formation lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively change the curvature of an image surface or the diameter of an optical spot, to reduce the bend of a scanning line and to realize fine optical scanning by constituting a scanning image formation lens of a single lens having a specific shape. SOLUTION: This scanning image formation lens 40A is composed of a single lens and the shapes of an incident side lens surface 41A and an exit side lens surface 41B are non-circular arc shapes. The lens surface 41A/41B is a WT surface and center axes x1 , x2 mutually form a finite angle in an XZ surface. The lens surface 41A inclines the axis x1 from the main light line FL of a deflected beam by an angle α1 (-) and is displaced only by a displacement amount Δ1 in a direction parallel with the rotational axis of a deflecting reflection surface. The lens surface 41B inclines the axis x2 by an angle α2 (-) and is displaced only by a displacement variable Δ2 in the direction parallel with the rotational axis of the deflecting reflection surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art An optical scanning device that deflects a light beam from a light source side at an equal angular velocity by an optical deflector and condenses the deflected light beam as a light spot on a surface to be scanned and performs optical scanning is a digital copier or a digital copier. It is widely known in connection with image forming apparatuses such as various printers. Conventionally, such an optical scanning device is generally
The light beam from the light source side and the surface on which the deflected light beam deflects and sweeps,
The optical arrangement is set so as to be on the same plane, and has the following problems. That is, first, the “floor area of the optical scanning device” increases. Secondly, a rotating polygon mirror is most commonly used as an optical deflector. However, since the rotation axis of the rotating polygon mirror is far from the deflecting / reflecting surface, the incident position of the light beam from the light source side to the deflecting / reflecting surface is reduced. A so-called “sag” occurs in which the deflection starting point of deflection of the deflected light beam fluctuates with the rotation of the deflective reflecting surface due to the rotation of the deflective reflecting surface. The direction of the realized deflecting light beam and the "direction of the incident light beam from the light source side to the deflecting / reflecting surface" form an angle of, for example, about 60 degrees.
Asymmetrically occur on both sides of the image, and it becomes necessary to asymmetrically correct curvature of field and “constant velocity characteristics such as fθ characteristics” in consideration of the influence of sag, and it becomes difficult to design a scanning imaging optical system.

As an optical arrangement which can solve these problems at once, a light beam from the light source side is applied to a deflecting and reflecting surface of an optical deflector.
The light is incident from a direction obliquely intersecting with the rotation axis of the deflecting / reflecting surface, is deflected at an equal angular velocity, and the deflected light beam is condensed as a light spot on the surface to be scanned. An optical arrangement that makes the optical scanning symmetric with respect to a plane including the rotation axis is conceivable. With this configuration, the optical system portion from the light source to the optical deflector and the optical system portion after the optical deflector can be laid out so as to be vertically overlapped, so that the floor area of the optical scanning device is reduced and the optical scanning device is reduced. Compactness can be achieved. Further, even if sag occurs, it occurs symmetrically at an image height of 0, so that it is easy to correct the constant velocity characteristics and the curvature of field.

However, such an optical arrangement has the following problems. That is, in order to make the light beam from the light source incident on the deflecting reflection surface of the optical deflector so as to obliquely intersect with the rotation axis of the deflecting reflection surface, the deflecting light beam is deflected so as to sweep the conical surface. The “position where the light beam enters the optical system thereafter” fluctuates to a considerable extent in the sub-scanning corresponding direction (the direction corresponding to the sub-scanning direction on the optical path from the light source to the surface to be scanned) due to the deflection. For this reason, the trajectory of the light spot on the surface to be scanned does not become a straight line, and so-called “scanning line bending” occurs.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an optical arrangement of a system in which a light beam from the light source side is incident on a deflecting reflection surface of an optical deflector from a direction obliquely intersecting the rotation axis of the deflecting reflection surface. It is an object of the present invention to realize good optical scanning by improving the variation in the curvature of field and the diameter of a light spot and effectively reducing the curvature of a scanning line by a scanning device.

[0006]

According to a scanning imaging lens of the present invention, "a light beam from a light source side is incident on a deflecting reflecting surface from a direction obliquely intersecting with a rotation axis of the deflecting reflecting surface at an incident angle θ. At the same time, a long line image is formed in the main scanning direction in the vicinity of the deflecting reflection surface, and the light beam reflected by the deflecting reflection surface is moved with respect to the plane formed by the principal ray of the light beam incident on the deflecting reflection surface and the rotation axis. A scanning imaging lens used in an optical scanning device that deflects symmetrically, converges a deflected light beam as a light spot on a surface to be scanned by a scanning image forming lens, and performs optical scanning of the surface to be scanned. It consists of a lens.

The scanning image forming lens according to the first aspect has the following features. Per incident-side lens surface, when the center axis x ₁ axis, a direction corresponding to the main scanning and y ₁ axis, x
Shape within ₁ y ₁ surface is non-arcuate shape. Per exit-side lens surface, the center axis x ₂ axis, a direction corresponding to the main scanning y ₂
When the axis, the shape of the x ₂ y ₂ surface which is non-arcuate shape.
The entrance-side lens surface (deflection / reflection surface-side lens surface) and / or the exit-side lens surface (scanned surface-side lens surface) are “WT surfaces”.
It is. The “WT plane” is a plane as described below. For example,
The case where the entrance lens surface is a WT surface will be described.
When a coordinate axis orthogonal to the above-mentioned coordinates: x ₁ y ₁ with respect to this lens surface is a z ₁ axis, a radius of curvature: r ₁ in a plane section parallel to the x ₁ z ₁ plane is determined by the y ₁ coordinate axis of this plane section. function:
The surface changes as r ₁ (y ₁ ). The x ₁ axis and x ₂ axes, forms a finite angle to each other in a plane containing them. That is, the x ₁ and x ₂ axes are in the same plane, but have different directions. Given the extreme where the x ₁ axis and x ₂ axes began to reduce the angle, but the same line conform to the x ₁ axis and x ₂ axes at this extreme, the straight line in the normal lens Corresponds to "optical axis."

For the following description, coordinate axes are set in the device space of the optical scanning device as follows. That is, the rotation axis of the deflecting / reflecting surface is defined as the Z-axis, and an axis orthogonal to the Z-axis within a plane including the principal ray of the light beam incident on the deflecting and reflecting surface and the Z-axis is defined as the X-axis.
An axis orthogonal to the X axis and the Z axis is defined as a Y axis. In this case, the principal ray of the light beam from the light source side is incident on the deflection reflecting surface in the XZ plane. If the incident angle of this incident light beam is θ, the principal ray of the incident light beam is , XY plane with respect to a plane parallel to the XY plane. The “main scanning corresponding direction” refers to a direction corresponding to the main scanning direction on the optical path from the light source to the surface to be scanned, but the Y axis direction corresponds to the main scanning corresponding direction, and the light flux from the light source side is the Y axis direction. Is formed as a long line image. The deflected light beam is
It will be symmetrically deflected to the XZ plane.

The scanning imaging lens according to the first aspect is provided in an optical scanning device as follows. As described above, since the y ₁ axis and the y ₂ axis “correspond to the main scanning”, the scanning imaging lens is set so that the y ₁ axis and the y ₂ axis are parallel to the Y axis. The plane containing the said x ₁ axis and x ₂ axis, is caused to conform to the XZ plane. A plane formed by the principal ray of the light beam incident on the deflecting reflection surface and the rotation axis of the deflecting reflection surface, that is, the principal ray of the deflecting light beam (having an angle θ with respect to the XY plane) in the XZ plane is incident. angular side lens surface x ₁ axis:
inclined by alpha _1, further x ₁ axis displacement in a direction parallel to the axis of rotation of the deflecting reflective surface (Z axis direction) is delta ₁ by displacement. Exit-side lens surface being an x ₂ axis with respect to the principal ray of the deflected light beam angle: Tilt alpha ₂ only, further x ₂ axis displacement in the Z direction: deployed is delta ₂ by displacement. At this time, the angles: α ₁ , α ₂ and the displacement amounts: Δ ₁ , Δ ₂ are used as correction parameters for scanning line bending, field curvature, and light spot diameter variation. That is, the lens shape (lens surface shape, thickness) of the scanning imaging lens is, a lens material (refractive index) is designed to satisfy the conditions requested scanning image forming lens, together with these, the alpha ₁ , Α ₂ , Δ ₁ , Δ ₂ are also used in the design as correction parameters.

As described above, in the scanning image forming lens according to the first aspect, at least one of the incident side lens surface and the exit side lens surface is a WT surface. Both are WT surfaces "(claim 2). In these according to claim 1 or 2 scanning imaging lens according, the focal length in the plane (XZ plane in the optical scanning apparatus) including the x ₁ axis and x ₂ axis f _Z
When the angles α ₁ and α ₂ are incident angles θ, the conditions are as follows: (1) 0.8 <| α ₁ /θ|<2.5 (2) 0.8 <| α ₂ /Θ|<2.5, and the displacement amounts: Δ ₁ , Δ ₂ and the focal length: f _Z are as follows: (3) 1 × 10 ² <| Δ ₁ / f _Z | <1 × 10 ¹ (4) It is preferable to satisfy 1 × 10 ² <| Δ ₂ / f _Z | <1 × 10 ¹ (claim 3).

The conditions (1) and (2) are conditions for effectively correcting the scanning line bending and effectively suppressing the fluctuation of the light spot diameter. In the case of the optical scanning device of the system in which the light beam from the light source side is incident on the deflection reflecting surface from a direction obliquely intersecting with the rotation axis of the deflection reflecting surface at an incident angle θ, the incidence angle θ
The smaller the is, the smaller the curvature of the scanning line becomes. However, in order to separate the incident light beam from the reflected light beam, a predetermined amount of the incident angle θ is required. The angles α ₁ and α ₂ are preferably proportional to θ, and the proportional coefficient is preferably in the range of the conditions (1) and (2) for the angles α ₁ and α ₂ . If the lower limits of the conditions (1) and (2) are exceeded, a sufficient scan line bending correction effect cannot be realized. If the upper limit of the conditions (1) and (2) is exceeded, the coma aberration in the sub-scanning direction becomes excessive in the middle to the peripheral image height of the light spot, and the wavefront aberration is deteriorated. As a result, the diameter of the light spot increases from the middle to the peripheral image height.

When the scanning image forming lens is tilted within the range of the conditions (1) and (2), the scanning line bending is effectively corrected as described above, but the coma aberration is caused by the lens tilt. Occurs. Conditions (3) and (4) are conditions for effectively correcting this coma. If the lower limit of the condition (3) or (4) is exceeded, the coma due to the inclination cannot be canceled,
The wavefront aberration deteriorates, and the fluctuation of the light spot diameter increases. If the upper limits of the conditions (3) and (4) are exceeded, the higher-order field curvature becomes large in the sub-scanning corresponding direction (the direction corresponding to the sub-scanning direction on the optical path from the light source to the surface to be scanned), and the light spot At the peripheral image height, the image plane rapidly falls to the scanning imaging lens side, so that the light spot diameter in the sub-scanning direction rapidly increases at the peripheral image height.

The scanning imaging lens according to the fourth aspect has the following features. When the optical axis is the x-axis and the direction corresponding to the main scanning is the y-axis, both the entrance-side lens surface and the exit-side lens surface have a non-circular shape in the xy plane. The entrance lens surface and / or the exit lens surface are WT surfaces. For the principal ray of the deflected light beam in the XZ plane,
The x-axis can be tilted by an angle: α, the incident-side lens surface has a displacement of the x-axis in the Z-axis direction: Δ ₁ , and the emission-side lens surface has a displacement of the x-axis in the Z-axis direction: Δ ₂ , respectively. It is displaced and deployed, and the angle: α and the displacement amounts: Δ ₁ , Δ ₂ are used as correction parameters for scanning line bending, field curvature, and light spot diameter variation. That is, the scanning imaging lens according to claim 4 is the scanning imaging lens according to claim 1, wherein the axis x
_1, x ₂ are matched in which becomes the optical axis (x-axis).

[0014] In the scanning imaging lens of the fourth aspect, the plane formed between the principal ray of the incident light beam on the deflection reflective surface and the deflection reflecting surface rotation axis: the focal length in the XZ plane f _Z
, The angle: α satisfies the condition: (5) 0.8 <| α / θ | <2.5 with respect to the incident angle: θ, the displacement amounts: Δ ₁ and Δ _2, and the focal length : f _Z condition: (6) 1 × 10 ~ 2 <| Δ 1 / f Z | <1 × 10 ~ 1 (7) 1 × 10 ~ 2 <| Δ 2 / f Z | <1 × 10 ~ 1 Is preferably satisfied (claim 5).

The condition (5) is a condition for effectively correcting the scanning line bending and effectively suppressing the fluctuation of the light spot diameter, as in the above conditions (1) and (2).
Sufficient scanning line bending correction effect cannot be realized,
If the upper limit is exceeded, the coma aberration in the sub-scanning direction becomes excessive at the middle to peripheral image heights of the light spot, the wavefront aberration deteriorates, and the light spot diameter at the intermediate to peripheral image heights is lower than the central image height. Becomes larger. The conditions (6) and (7) correspond to the conditions (3) and (3).
Similar to (4), this is a condition for effectively correcting coma caused by lens tilt. If the lower limit of conditions (6) and (7) is exceeded, coma due to the tilt cannot be canceled, and wavefront aberration is reduced. When the light spot diameter is deteriorated and the fluctuation of the light spot diameter becomes large, and exceeds the upper limit of the conditions (6) and (7), the higher-order field curvature becomes large in the sub-scanning corresponding direction, and Since the surface quickly falls to the scanning image forming lens side, the light spot diameter in the sub-scanning direction rapidly increases at the peripheral image height.

Each of the scanning image forming lenses according to any one of the first to fifth aspects has a "function of equalizing the speed of light scanning of a surface to be scanned by a deflected light beam deflected at a constant angular velocity". (Claim 6). Further, any of the scanning imaging lenses according to any one of claims 1 to 6 emits a deflected light beam, which has been formed into a "long line image in the main scanning corresponding direction", on the surface to be scanned in the vicinity of the deflecting reflection surface. Since the light is condensed as a spot, it has a function of making the vicinity of the deflecting reflection surface position and the position of the surface to be scanned conjugate with respect to the sub-scanning corresponding direction. 8) It is preferable to satisfy the following condition: 2 <| m | <6 (claim 7) In other words, when the lower limit is exceeded, the arrangement of the scanning imaging lens approaches the surface to be scanned, so that the scanning imaging lens moves in the Y direction. If the length exceeds the upper limit, an error in the X-axis direction in the deflecting reflecting surface is propagated to the surface to be scanned in the form of “m ² ” when the upper limit is exceeded. High precision is required for the precision and surface precision, which causes an increase in cost.

According to the optical scanning device of the present invention, "the light beam from the light source side is incident on the rotation axis (Z-axis) of the deflecting / reflection surface at an incident angle θ
In this case, the light is made incident on the deflecting reflection surface from a direction intersecting obliquely, and a long line image is formed in the vicinity of the deflecting reflection surface in the main scanning direction (Y-axis direction). The deflecting light beam is symmetrically deflected with respect to a plane (XZ plane) formed by the principal ray of the incident light beam and the rotation axis, and the deflected light beam is condensed as a light spot on the surface to be scanned by the scanning imaging lens. Optical scanning device that performs optical scanning of The optical scanning device according to claim 8 has the following features. That is, the scanning imaging lens according to claim 1, 2 or 3 is used as the scanning imaging lens, and the material and shape and angles of the scanning imaging lens are α ₁ and α ₂ , and the displacement amounts are Δ ₁ and Δ _2.
By adjusting (1), the curvature of field, the curvature of the scanning line, and the variation of the light spot diameter are suppressed within the allowable ranges. Claim 9
The described optical scanning device has the following features. That is, the scanning image forming lens according to claim 4 is used as the scanning image forming lens, and the image plane is adjusted by adjusting the material and shape of the scanning image forming lens and the angle α and the displacement amounts Δ ₁ and Δ _2. Curve, scan line bend, and fluctuation of light spot diameter are suppressed within allowable ranges, respectively. In the optical scanning device according to the eighth or ninth aspect, the scanning image forming lens may have a function of “equalizing the optical scanning of the surface to be scanned by the deflected light beam deflected at a constant angular velocity”. 10), paraxial magnification in the conjugate relationship in the sub-scanning corresponding direction: m
Can satisfy the following condition: (8) 2 <| m | <6 (claim 11).

[0018]

FIG. 1 is a diagram for explaining an embodiment of an optical scanning device according to the present invention. In FIG. 1A, reference numeral 10 denotes a semiconductor laser as a “light source”, reference numeral 15 denotes a coupling lens, reference numeral 20 denotes an aperture,
Reference numeral 25 denotes a cylindrical lens, reference numeral 30 denotes a rotating polygon mirror as an “optical deflector”, reference numeral 31 denotes a deflecting reflection surface, reference numeral 30AX denotes a rotation axis of the deflecting reflection surface 31 (a rotation axis of the rotation polygon mirror 30 itself), and reference numeral 40 Denotes a scanning imaging lens, and reference numeral 50 denotes a surface to be scanned (actually, a photosensitive surface of a photoconductive photoconductor).

The luminous flux emitted from the semiconductor laser 10 is
The light is coupled to the subsequent optical system by the coupling lens 15. The coupled light beam can be a parallel light beam, a convergent light beam, or a divergent light beam depending on the optical characteristics of the optical system thereafter. The coupled beam is aperture 2
When passing through zero, the peripheral light beam part is removed and so-called “beam shaping” is performed. The beam-shaped light beam is converged by the cylindrical lens 25 in the direction corresponding to the sub-scanning, and is formed on the position of the deflecting reflection surface 31 as a long line image in the direction corresponding to the main scanning. The luminous flux reflected by the deflecting / reflecting surface 31 is applied to the rotating polygon mirror 30.
Becomes a deflected light beam deflected at a constant angular velocity with the constant speed rotation, forms a light spot on the surface 50 to be scanned by the scanning imaging lens 40, and optically scans the surface 50 to be scanned. FIG. 1 (a)
, The "Z-axis" is set in accordance with the rotation axis 30AX of the rotary polygon mirror 30, and the X and Y directions are determined as shown in the figure. Then, (the principal ray) of the light beam incident on the deflection reflection surface 31 from the semiconductor laser 10 side and the rotation axis 30AX are in the same plane, that is, in the “XZ plane”. The Y direction is a “main scanning corresponding direction”.

FIG. 1B shows the state of FIG. 1A as viewed from the Y direction, and the plane of FIG. 1B is an "XZ plane". As shown in (b), the principal ray of the light beam from the semiconductor laser 10 is incident on the deflecting / reflecting surface 31 at an incident angle θ with respect to the rotation axis 30AZ of the deflecting / reflecting surface 31 in the XZ plane. . That is, the incident angle: θ is the rotation axis 3
The angle formed by the principal ray of the incident light beam with respect to a plane (XY plane) orthogonal to 0AX. In FIG. 1B, the angle of incidence: θ is indicated as θ (−), which means that the incident light beam enters the plane perpendicular to the rotation axis 30AX from the “negative side” in the Z direction. I have. As is clear from FIG. 1A, the optical scanning of the surface 50 to be scanned is substantially symmetric with respect to the XZ plane, that is, "symmetric with respect to the XZ plane" according to the rotation of the rotary polygon mirror 30.
Done in That is, the optical scanning device according to the embodiment shown in FIG. 1 is configured such that “the light beam from the light source 10 side obliquely intersects the rotation axis (Z axis) of the deflecting / reflecting surface 31 at an incident angle θ.
While being incident on the deflecting / reflecting surface 31, an image is formed in the vicinity of the deflecting / reflecting surface into a long linear image in the main scanning direction (Y direction), and the light beam reflected by the deflecting / reflecting surface 31 is converted into a principal ray of the incident light beam on the deflecting / reflective surface. And the rotation axis are symmetrically deflected with respect to a plane (XZ plane) formed by the scanning axis, and the deflected light beam is condensed as a light spot on the surface 50 to be scanned by the scanning image forming lens 40. An optical scanning device that performs optical scanning ”(claims 8 and 9), and when the scanning imaging lens 40 is the scanning imaging lens according to claim 1, 2 or 3, the optical scanning device becomes the optical scanning device according to claim 8. , Scanning imaging lens 40
Is a scanning image forming lens according to claim 4 or 5, the optical scanning device according to claim 9 is provided.

FIG. 2 is a view for explaining the shape of the scanning image forming lens according to the first aspect and the arrangement in the optical scanning device. The lens 40A used as the scanning imaging lens 40 in the embodiment of FIG.
When x ₁ axis center axis per incident-side lens surface 41A, a direction corresponding to the main scanning (the direction perpendicular to the drawing) and y ₁ axis, the shape of the x ₁ y ₁ plane is a non-arcuate shape. Also when x ₂ axis center axis per exit-side lens surface 41B, the direction corresponding to the main scanning and y ₂ axes, the shape of the x ₂ y ₂ surface which is non-arcuate shape. Incident-side lens surface 41A and / or the exit side lens surface 41B is WT surface, and the x ₁ axis and x ₂ axis,
They form finite angles with each other in a plane including these (the XZ plane in the figure). With respect to the principal ray FL of the deflecting light beam in a plane (XZ plane) formed by the principal ray of the light beam incident on the deflecting reflection surface and the rotation axis (Z axis) of the deflecting reflection surface, the entrance lens surface 41A.
The x ₁ axis corner: (-) alpha ₁ with tilting only, x ₁ axis displacement in a direction parallel to the axis of rotation of the deflecting reflective surface: is displaced by delta _1, the exit-side lens surface 41B of the x ₂ axis Angle: α ₂ (−), and the x ₂ axis is displaced by Δ _{2 in} a direction parallel to the rotation axis of the deflecting / reflecting surface. These angles: α ₁ , α ₂ , and the displacement amounts: Δ ₁ , Δ ₂ are used as correction parameters for scanning line bending, field curvature, and light spot diameter variation.

FIG. 3 is a view for explaining the shape of the scanning image forming lens according to the fourth aspect and the arrangement in the optical scanning device. The lens 40B used as the scanning imaging lens 40 in the embodiment of FIG.
When the optical axis is the x-axis and the direction corresponding to the main scanning (the direction orthogonal to the drawing) is the y-axis, both the entrance-side lens surface 42A and the exit-side lens surface 42B have a non-arc shape in the xy plane. is there. The entrance-side lens surface 42A and / or the exit-side lens surface 42B are WT surfaces, and are in a plane (XZ plane) formed by the principal ray of the light beam incident on the deflecting / reflecting surface and the deflecting / reflecting surface rotation axis (Z-axis). The x-axis is inclined by an angle α (−) with respect to the principal ray FL of the deflected light beam, and the incident-side lens surface 42A is displaced in the x-axis direction parallel to the rotation axis of the deflective reflection surface: Δ ₁ However, the exit-side lens surface 42B is
The amount of displacement of the x-axis in a direction parallel to the rotation axis of the deflecting reflection surface: Δ ₂
Only each is displaced and deployed. These angles: α,
The displacement amounts: Δ ₁ and Δ ₂ are used as correction parameters for scanning line bending, field curvature, and light spot diameter variation.
In the description according to FIGS. 2 and 3, (−) added to the angles α ₁ and α ₂ means that the clockwise angle with respect to the principal ray FL is negative, and the angle added to the angle θ. (+) Means that the counterclockwise angle with respect to the X axis is positive. In the embodiment described above, the incident angle: θ, the inclination angle: α ₁ ,
It should be noted that, of course, an optical arrangement in which the signs of α ₂ and displacement amounts: Δ ₁ and Δ ₂ are inverted as a whole is also possible.

[0023]

EXAMPLES Three specific examples will be described below.

Each embodiment is an embodiment of the embodiment shown in FIG. The semiconductor laser as the light source 10 has an emission wavelength of 780 nm. The coupling lens 15 has a focal length of 9 mm and NA = 0.3, the coupling action is a “collimating action”, and the coupled light flux is a “substantial parallel light flux”. Aperture 20
Has a circular opening having an opening diameter of 3 mm, and the cylindrical lens 25 has a focal length of 6 in the sub-scanning corresponding direction.
0 mm “plano-convex lens”, and the luminous flux from the light source side is substantially parallel in the main scanning corresponding direction near the surface to be scanned.
The light is condensed in the sub-scanning corresponding direction, and is a long line image as a whole in the main scanning corresponding direction (Y direction). In such an optical system layout, the allowable range of the curvature of field is within ± 1 mm in both the main and sub-scanning directions, the allowable range of the scanning line bending is within 0.1 mm, and the fluctuation of the light spot diameter is both in the main and sub-scanning directions. 3.5 μm or less, and the lens surface shape of the scanning imaging lens 40, such that performance within these allowable ranges is realized.
Incline angles: α, α ₁ , α ₂ , displacement amounts: Δ ₁ , Δ ₂ , incident angle:
Determined according to θ.

A description will now be given of the specification of the shape and arrangement of the scanning imaging lens. In the first embodiment, the one described in claim 3 is used as a scanning imaging lens.
In the second and third embodiments, the structure described in claim 5 is used. In any of Embodiments 1 to 3, the lens surface of the scanning imaging lens is a “WT surface”. The “non-circular shape” of each surface is obtained by a well-known formula: x (y) = (y ² / R) / [1 + √ {1- (1 + K) (y / R) ² }] A ₀ · y ² + A · ^{y 4 + B · y 6 +} C · y 8 + D · y 10 +. . . , The paraxial radius of curvature: R and the constants: K, A ₀ , A,
B, C, D,. Give. To identify. In the case where the scanning imaging lens is the one described in claim 5, "x" in this equation is a coordinate corresponding to the optical axis, and "y" is a coordinate corresponding to the main scanning direction. Further, when the scanning imaging lens is of the third aspect "x, y", "x _1, y _1" for the incident-side lens surface, with respect to the exit-side lens surface "x _2, y ₂ '
Is used. Further, the function shape of the radius of curvature Y in the plane parallel to the XZ plane that specifies the WT plane that is the “special toric plane”: r _i (y) is an even-order polynomial: r _i (y) = a +
b · y ² + c · y ⁴ + d · y ⁶ + e · y ⁸ + f · y ¹⁰ + g ·
y ¹² +. . At each coefficient: a, b,. . . , G. .
To identify. i is i =
1, i = 2 for the exit-side lens surface.

[0026] In each example, scanning the material refractive index of the imaging lens (that for a wavelength of 780nm light) to "n _780", in the XZ plane of the optical scanning device (xz plane, x ₁ z
When the lens thickness in _one plane or x ₂ z ₂ side) (scanning imaging lens is of the claimed response 3 described, the distance) between the origin of the origin and y ₂ axes y ₁ axis and d (0) I do.

Further, (straight line in FIG. 12: FL) principal ray of the deflected light beam in the XZ plane with respect to the state of being deployed by matching the x-axis or x ₁ axis and a "reference state",
In this reference state, the distance in the X-axis direction where the incident-side lens surface is located is “S (0)”, and the distance in the X-axis direction between the exit-side lens surface and the surface to be scanned is “l (0)”. . The unit of the quantity having the dimension of distance is “mm”.

Embodiment 1 S (0) = 45.5, d (0) = 13.2, l (0) = 172.2, n ₇₈₀ = 1.52441, θ
(+) = 0.0806 rad incident-side lens surface: non-arcuate shape of the WT surface x ₁ y ₁ plane R = 208.373, K = -6.077E + 1, A 0 = -1.879E-4, A = -5.031E- 7, B =
1.261E-10, C = -4.089E- 14, D = 2.987E-18 r 1 (y 1) a = -165.05, b = 5.579E-2, c =
−2.019E-4, d = 5.043E-7, e =
−8.302E−10, f = 6.326E−13
, G = -1.831E-16 exit-side lens surface: non-arcuate shape R = -152.69 of WT surface x ₂ y _{2 plane, K = 0.9840, A 0 =} -4.044E-4, A = -7.295E- 7, B
= 1.495E-10, C = -7.287E-140, D = 5.104E-18 r ₂ (y ₂ ) a = -19.833, b = -6.700E-4, c = 1.093E-6, d = 6.400E -1
0, e = -3.381E-12, f = 3.126E-15, g = -9.374E-19 α ₁ = 0.122 rad α ₂ = 0.1145 rad, Δ ₁ = −
2.429 mm, Δ ₂ = -1.927 mm
.

The change in spherical aberration (wavefront aberration) according to the image height in the first embodiment is shown below. Image height Wavefront aberration (RMS) (mm) (λ = 780 nm) 0 0.0086 35 0.0149 58 0.0129 82 0.0173 93 0.0133 105 0.0122 Conditions (1) to (4), (8) ) Parameter value: | α ₁ /θ|=1.51 | α ₂ /θ|=1.42 | Δ ₁ / f _Z | = 5.83E-2 | Δ ₂ / f _Z | = 4.62E −2 | m | = 3.10 (f _Z = 41.7) FIG. 4 shows field curvature (solid line in the sub-scanning direction, broken line in the main scanning direction), scanning line bending, linearity, and fθ characteristics according to the first embodiment. FIG. From these, the embodiment is not limited to the scan line curve, but also the field curvature and linearity and f.
The θ characteristic is also satisfactorily corrected. In the above data notation, for example, “E-9” means “10 to ⁹ ”.
The same applies hereinafter.

Example 2 S (0) = 45.5, d (0) = 13.0, l (0) = 176.8, n ₇₈₀ = 1.52441,
θ (+) = 0.0806 rad Incident lens surface: WT surface Non-circular shape in xy plane R = 207.192, K = -6.044E + 1, A ₀ = -1.396E-4, A = -5.034E
-7, B = 1.258E-10, C = -4.098E-14, D = 2.917E-18 r ₁ (y ₁ ) a = -161.55, b = 5.924E-2, c = -2.016E-4, d = 3.759E-
7, e = -6.073E-10, f = 4.929E-13, g = -1.540E-16 Exit side lens surface: WT surface Non-circular shape in xy plane R = -152.94, K = 0.9844, A ₀ = -3.655E-4, A = -7.305E-
7, B = 1.493E-10, C = -7.292E-14, D = 5.102E-18 r ₂ (y ₂ ) a = -19.862, b = -7.272E-4, c = 1.087E-6, d = 1.215E-
9, e = -4.674E-12, f = 5.502E-15, g = -1.690E-18 α = 0.1306 rad Δ ₁ = -2.247 mm, Δ ₂ = -1.694 mm
.

The change in spherical aberration (wavefront aberration) according to the image height in the second embodiment is shown below. Image height Wavefront aberration (RMS) (mm) (λ = 780 nm) 0 0.0144 35 0.0153 58 0.0141 82 0.0154 93 0.0121 105 0.0129 Conditions (5), (6) to (8) parameter values): | α / θ | = 1.62 | Δ 1 / f Z | = 5.36E-2 | Δ 2 / f Z | = 4.04E-2 | m | = 3.19 (f _Z = 41.9) FIG. 5 is a diagram showing the field curvature (solid line is in the sub-scanning direction, broken line is in the main scanning direction), scanning line bending, linearity, and fθ characteristics according to the second embodiment. From these, the embodiment is not limited to the scan line curve, but also the field curvature and linearity and f.
The θ characteristic is also satisfactorily corrected.

[0032] Example 3 S (0) = 46.3, d (0) = 11.5, l (0) = 174.8, n 780 = 1.52441
, θ (+) = 0.0605 rad Incident lens surface: WT surface Non-circular shape in xy plane R = 205.770, K = -5.691E + 1, A ₀ = -3.317E-5, A = -5.027E
-7, B = 1.255E-10, C = -4.056E-14, D = 3.090E-18 r ₁ (y ₁ ) a = -168.84, b = 6.330E-2, c = -2.024E-4, d = 3.754E-
7, e = -4.920E-10, f = 3.226E-13, g = -8.142E-17 Exit lens surface: WT surface Non-circular shape in xy plane R = -154.17, K = 1.092, A ₀ = -1.841E-4, A = -7.253E-7 B = 1.527E-10, C = -7.271E-14, D = 5.090E-18 r ₂ (y ₂ ) a = -19.761, b = -8.503E -4, c = 1.064E-6, d = 3.593E-
9, e = -2.381E-12, f = 2.117E-15, g = -5.788E-19 α = 0.0985 rad Δ ₁ = −2.146 mm, Δ ₂ = −1.132 mm
.

The change in spherical aberration (wavefront aberration) according to the image height in the third embodiment is shown below. Image height Wavefront aberration (RMS) (mm) (λ = 780 nm) 0 0.0197 35 0.0195 58 0.0210 82 0.0198 93 0.0205 105 0.0175 Conditions (5), (6) to (8) parameter values): | α / θ | = 1.63 | Δ 1 / f Z | = 5.16E-2 | Δ 2 / f Z | = 2.72E-2 | m | = 3.18 (f to _Z = 41.6) 6, curvature (solid lines for example 3 is the sub-scanning direction, and the broken line the main scanning direction), scanning line bending, shows a diagram of the linearity and fθ characteristics. From these, the embodiment is not limited to the scan line curve, but also the field curvature and linearity and f.
The θ characteristic is also satisfactorily corrected.

That is, in the first embodiment, as the optical scanning device, the light beam from the light source side is incident on the deflecting reflection surface from a direction obliquely intersecting the rotation axis of the deflecting reflection surface at an incident angle θ. A linear image is formed in the vicinity of the deflecting reflection surface in a direction corresponding to the main scanning, and the light beam reflected by the deflecting reflection surface is symmetric with respect to the plane formed by the principal ray of the light beam incident on the deflecting reflection surface and the rotation axis. 4. The optical scanning device according to claim 3, wherein the optical scanning device performs optical scanning on the surface to be scanned by converging the deflected light beam as a light spot on the surface to be scanned by the scanning image forming lens. Using a scanning imaging lens, the material and shape and angles of the scanning imaging lens: α ₁ , α ₂ ,
By adjusting the displacement amounts: Δ ₁ and Δ ₂ , the curvature of field, the curvature of the scanning line, and the variation of the light spot diameter are suppressed within allowable ranges, respectively (claim 8). As the optical scanning device, a light beam from the light source side is incident on the deflecting reflecting surface in a direction obliquely intersecting with the rotation axis of the deflecting reflecting surface at an incident angle: θ, and in the main scanning corresponding direction near the deflecting reflecting surface. An image is formed on a long line image, and the light beam reflected by the deflecting / reflecting surface is symmetrically deflected with respect to the plane formed by the principal ray of the light beam incident on the deflecting / reflecting surface and the rotation axis.
In an optical scanning device that converges as a light spot on a surface to be scanned by a scanning imaging lens and performs optical scanning of the surface to be scanned,
The scanning imaging lens according to claim 5 is used as the scanning imaging lens, and the material, shape, and angle of the scanning imaging lens are as follows:
By adjusting α and the amount of displacement: Δ ₁ and Δ ₂ , the curvature of field, the curvature of the scanning line, and the variation of the light spot diameter are suppressed within allowable ranges, respectively. In each embodiment,
The scanning imaging lens has a function of making the optical scanning of the surface to be scanned uniform by a deflected light beam deflected at a uniform angular velocity (claim 10), and has a paraxial magnification in a conjugate relationship in the sub-scanning corresponding direction. : M satisfies the condition (8).
1).

[0035]

As described above, according to the present invention, a novel scanning imaging lens and optical scanning device can be realized. As described above, the scanning imaging lens according to the present invention has an angle: α
Alternatively, by using α ₁ , α ₂ and Δ ₁ , Δ ₂ as correction parameters such as scanning line curvature and field curvature, the scanning line curvature of the oblique incidence type optical scanning device can be effectively corrected, and the image plane can be corrected. Good optical scanning can be realized by effectively suppressing the curvature and the fluctuation of the light spot diameter. The scanning imaging lens according to any one of claims 1 to 3 can be easily and inexpensively manufactured by plastic molding. Further, as described above, the optical scanning device of the present invention has an optical arrangement of a system in which the light flux from the light source side is incident on the deflecting reflection surface of the optical deflector from a direction obliquely intersecting the rotation axis of the deflecting reflection surface. Since the floor area of the optical scanning device can be made smaller and smaller, and the generated sag is symmetrical on both sides of the image height 0 of the light spot, it can be said that the scanning imaging lens includes a special toric surface (WT surface). It can be realized as a relatively easy-to-manufacture lens that is symmetrical with the optical axis in the scanning corresponding direction.By using this scanning imaging lens, it is possible to satisfactorily correct the scanning line bending and image field strength and reduce the fluctuation of the light spot diameter. As a result, good optical scanning can be realized. Claims 6 and 1
In the invention described in No. 0, it is possible to effectively correct the scanning line bending, maintain the light spot shape appropriately, correct the field curvature and the light spot diameter well, and realize the uniform speed of the optical scanning,
According to the seventh and eleventh aspects of the present invention, the positional accuracy and the surface accuracy of the deflecting reflection surface can be reduced without increasing the length of the scanning imaging lens.

[Brief description of the drawings]

FIG. 1 is a diagram for describing one embodiment of the present invention.

FIG. 2 is a view for explaining the shape of the scanning image forming lens according to the first embodiment and a state of being arranged in an optical scanning device.

FIG. 3 is a diagram for explaining the shape of a scanning image forming lens according to claim 4 and a state of being arranged in an optical scanning device.

FIG. 4 is a diagram illustrating the field curvature, scanning line curve, linearity, and fθ characteristics according to the first embodiment.

FIG. 5 is a diagram illustrating field curvature, scanning line curve, linearity, and fθ characteristics according to the second embodiment.

FIG. 6 is a diagram illustrating field curvature, scanning line curve, linearity, and fθ characteristics according to the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Semiconductor laser 15 Coupling lens 25 Cylindrical lens 30 Rotating polygon mirror 31 Deflection / reflection surface 30AX Rotation axis of deflection / reflection surface 40 Scanning imaging lens 50 Scanned surface

Claims (11)

[Claims] A luminous flux from a light source side is made incident on the deflecting reflective surface from a direction obliquely intersecting the rotation axis of the deflecting reflective surface at an incident angle of θ, and in the main scanning corresponding direction near the deflecting reflective surface. Formed on a long line image, the reflected light beam by the deflecting and reflecting surface is symmetrically deflected with respect to the plane formed by the principal ray of the light beam incident on the deflecting and reflecting surface and the rotation axis,
A scanning image forming lens used in an optical scanning device that converges a deflected light beam as a light spot on a surface to be scanned by a scanning image forming lens and performs optical scanning of the surface to be scanned, comprising a single lens, When the central axis is x ₁ axis and the direction corresponding to the main scanning is y ₁ axis, the shape in the x ₁ y ₁ plane is a non-circular shape, and the exit lens surface is , the central axis x ₂ axis, a direction corresponding to the main scanning when the y ₂ axis, a non-arc shape shapes in x ₂ y ₂ surface, incident-side lens surface and / or the exit side lens surface a WT surface, and the x ₁ axis and x ₂ axis, without the finite angles to each other in a plane including these, a plane formed between the principal ray and the rotation axis of the incident light beam to said deflective reflection surface the main ray of the deflected light beam at said entrance-side lens surface being an x ₁ axis angle: tilt α by ₁ Along with
x ₁ displacement in the direction parallel to the rotation axis of the deflecting and reflecting surface: Δ ₁
Is only displaced, the exit side lens surface of the x ₂ axis and angle with tilting alpha ₂ only, x ₂ axis displacement in a direction parallel to the axis of rotation of the deflecting reflective surface: deployed is displaced by delta _2, the A scanning imaging lens wherein angles: α ₁ , α ₂ and displacement amounts: Δ ₁ , Δ ₂ are used as correction parameters for scanning line bending, field curvature, and light spot diameter variation. 2. The scanning imaging lens according to claim 1, wherein both the entrance and exit lens surfaces are WT surfaces. 3. An apparatus according to claim 1 or 2 scanning imaging lens according, when the focal length in the plane containing the x ₁ axis and x ₂ axis and f _Z, angle: alpha _1, alpha ₂ is incident angle: with respect to theta, conditions: (1) 0.8 <| α 1 /θ|<2.5 (2) 0.8 <| α 2 /θ|<2.5 satisfied, displacement: Δ ₁ , Δ ₂ and focal length: f _Z are conditions: (3) 1 × 10 ² <| Δ ₁ / f _Z | <1 × 10 ¹ (4) 1 × 10 ² <| Δ ₂ / f _Z | <scanning and imaging lens satisfies the ¹ × 10 ~ 1. 4. A luminous flux from the light source side is made incident on the deflecting reflection surface from a direction obliquely intersecting the rotation axis of the deflecting reflection surface at an incident angle θ, and in the main scanning corresponding direction near the deflecting reflection surface. Formed on a long line image, the reflected light beam by the deflecting and reflecting surface is symmetrically deflected with respect to the plane formed by the principal ray of the light beam incident on the deflecting and reflecting surface and the rotation axis,
A scanning image forming lens used in an optical scanning device that converges a deflected light beam as a light spot on a surface to be scanned by a scanning image forming lens and performs optical scanning of the surface to be scanned, comprising a single lens, When the optical axis is the x axis and the direction corresponding to the main scanning is the y axis,
Both the entrance-side lens surface and the exit-side lens surface have a non-circular shape in the xy plane, and the entrance-side lens surface and / or the exit-side lens surface are WT surfaces. For the principal ray of the deflected light beam in the plane formed by the ray and the rotation axis, x
The axis is tilted by an angle: α, and the incident-side lens surface is displaced in the direction parallel to the rotation axis of the deflecting / reflecting surface with respect to the x-axis.
Only delta _1, the exit side lens surface displacement in the direction parallel to the axis of rotation of the deflecting reflective surface in the x-axis: delta by _2, is deployed are respectively displaced, the angle: alpha, displacement: delta _1, delta _2. A scanning imaging lens, wherein ₂ is used as a correction parameter for scanning line bending, field curvature, and light spot diameter variation. 5. The scanning imaging lens according to claim 4, wherein a focal length in a plane formed by the principal ray of the light beam incident on the deflecting / reflecting surface and the rotation axis is _fZ, and an angle: α Satisfies the condition: (5) 0.8 <| α / θ | <2.5 with respect to the incident angle θ, and the displacement amounts: Δ ₁ , Δ ₂ and the focal length: f _Z are: 6) 1 × 10 ² <| Δ ₁ / f _Z | <1 × 10 ¹ (7) It is characterized by satisfying 1 × 10 ² <| Δ ₂ / f _Z | <1 × 10 ¹ Scanning imaging lens. 6. A scanning image forming lens according to claim 1, wherein the scanning image forming lens has a function of equalizing the speed of light scanning of a surface to be scanned by a deflected light beam deflected at a constant angular velocity. Scanning imaging lens. 7. A scanning image forming lens according to claim 1, further comprising a function of making the vicinity of the position of the deflecting reflection surface and the position of the surface to be scanned conjugate in the sub-scanning corresponding direction. And a paraxial magnification: m in the conjugate relationship satisfies the following condition: (8) 2 <| m | <6. 8. A luminous flux from the light source side is made incident on the deflecting reflection surface from a direction obliquely intersecting with the rotation axis of the deflecting reflection surface at an incident angle of θ, and in the main scanning direction near the deflecting reflection surface. Formed on a long line image, the reflected light beam by the deflecting and reflecting surface is symmetrically deflected with respect to the plane formed by the principal ray of the light beam incident on the deflecting and reflecting surface and the rotation axis,
4. An optical scanning device for converging a deflected light beam as a light spot on a surface to be scanned by a scanning image forming lens and performing optical scanning on the surface to be scanned, wherein the scanning image forming lens is used as a scanning image forming lens. By using a scanning imaging lens and adjusting the material and shape of the scanning imaging lens and the angles α ₁ , α ₂ and the displacement amounts Δ ₁ , Δ ₂ , the curvature of field, the bending of the scanning line, and the fluctuation of the light spot diameter can be reduced. An optical scanning device characterized in that each is within an allowable range. 9. A luminous flux from the light source side is made incident on the deflecting reflecting surface from a direction obliquely intersecting with the rotation axis of the deflecting reflecting surface at an incident angle θ, and in the main scanning direction in the vicinity of the deflecting reflecting surface. Formed on a long line image, the reflected light beam by the deflecting and reflecting surface is symmetrically deflected with respect to the plane formed by the principal ray of the light beam incident on the deflecting and reflecting surface and the rotation axis,
6. An optical scanning device for converging a deflected light beam as a light spot on a surface to be scanned by a scanning image forming lens and performing optical scanning on the surface to be scanned, wherein the scanning image forming lens is used as a scanning image forming lens. By using an image lens and adjusting the material and shape of the scanning imaging lens and the angle: α, and the amount of displacement: Δ ₁ , Δ ₂ , the curvature of field, the curvature of the scanning line, and the variation of the light spot diameter are all within allowable ranges. An optical scanning device characterized by being suppressed. 10. The optical scanning device according to claim 9, wherein the scanning image forming lens has a function of making optical scanning of the surface to be scanned uniform by a deflected light beam deflected at a uniform angular velocity. Optical scanning device. 11. The optical scanning device according to claim 8, wherein the scanning imaging lens has a function of making the vicinity of the position of the deflecting reflection surface and the position of the surface to be scanned conjugate in the sub-scanning corresponding direction. An optical scanning device, wherein the paraxial magnification: m in the conjugate relationship satisfies the following condition: (8) 2 <| m | <6.