JPH0764005A - Scanning device - Google Patents

Abstract

PURPOSE:To provide a scanning device capable of excellently correcting a distortion aberration and a main scaning direction image surface curvature and whose surface shape of an ftheta lens is simple and easy for working. CONSTITUTION:This device is the scanning device using the single glass ftheta lens 4 and on which a converged luminous flux is made incident. The single glass ftheta lens 4 is a biconvex lens in a main scanning direction, and main scanning direction main curves of first and second surfaces are formed in a circle, or the main scanning direction main curve of at least one side surface is formed in a curve whose radius of curvature becoming larger or smaller according to that a main scanning direction viewing angle becomes larger. Further, in the scanning device, an interval between a deflection surface of a deflector 3 and the first surface of the single glass ftheta lens 4, the interval between the second surface of the single glass ftheta lens 4 and a surface to be scanned and the main scanning direction focal distance of the single glass ftheta lens 4 are set properly. Further, the main scanning direction radiuses of curvature of respective surfaces of the single glass ftheta lens 4, the refractive index of the single glass ftheta lens, a distance from the front side main point of the single glass ftheta lens 4 to the deflection surface of the deflector 3 and the distance from the front side main point of the single glass ftheta lens 4 to the natural converged point of the converged luminous flux are set properly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning device for forming an image of a light beam deflected at a constant angular velocity by a deflector on a surface to be scanned and scanning the surface to be scanned at a substantially constant speed.

[0002]

2. Description of the Related Art A scanning device for scanning a surface to be scanned by deflecting a light beam by a deflector such as a polygon mirror is used in a laser beam printer, a digital copying machine and the like. In such a scanning device, uniform speed of scanning on the surface to be scanned is desired. Conventionally, in order to realize this constant velocity property, an fθ lens is arranged between the deflector and the scanned object.

A large number of scanning devices using the f.theta. Lens composed of a plurality of lenses have been proposed and put into practical use. On the other hand, as a simpler one, a scanning device using a single-lens fθ lens is disclosed in JP-A-3-21381.
No. 2 and Japanese Patent Laid-Open No. 4-50908.

In the scanning device disclosed in Japanese Unexamined Patent Publication (Kokai) No. 3-213812, a single biconvex lens or a positive meniscus lens is used as an fθ lens, and a convergent light beam is incident on this fθ lens. On the other hand, the above-mentioned JP-A-4-509.
In the scanning device disclosed in Japanese Patent Laid-Open No. 08-08, an fθ lens whose both surfaces are aspherical surfaces is used, and a convergent light beam is incident on this fθ lens. In the scanning devices disclosed in both publications, the convergent light beam is made incident on the fθ lens because when a parallel light beam is made incident on the fθ lens, a surface shape in the main scanning direction is obtained in order to obtain a refracting power in the main scanning direction. This is because it must be specified and distortion and field curvature in the main scanning direction cannot be corrected sufficiently.

[0005]

However, in the scanning device disclosed in Japanese Patent Laid-Open No. 3-213812, the correction of the distortion aberration is not sufficient, and the desired constant velocity cannot be obtained. On the other hand, in the scanning device disclosed in Japanese Unexamined Patent Publication No. 4-50908, both sides of the single-lens fθ lens are aspherical, and the aspherical shape is very complicated, and there is a problem that processing is difficult.

Therefore, the present invention can satisfactorily correct the distortion and the field curvature in the main scanning direction, and f
It is an object of the present invention to provide a scanning device in which the surface shape of a θ lens is simple and easy to process.

[0007]

The present invention is a scanning device that uses a single-lens f.theta. Lens and makes a convergent light beam enter the single-lens f.theta. Lens. The single-lens fθ lens in the present invention is a biconvex lens in the main scanning direction, and the main scanning direction main curve of the first surface and the second surface is formed by a circle, or at least one surface of the main scanning direction main curve. The curve is formed by a curve whose radius of curvature increases or decreases as the angle of view in the main scanning direction increases. Further, in this scanning device, the distance between the deflecting surface of the deflector and the first surface of the single-lens fθ lens,
Single lens fθ Distance between second surface of lens and scanned surface and single lens fθ
The focal length of the lens in the main scanning direction is set appropriately. As required, the radius of curvature of each surface of the single-lens fθ lens in the main scanning direction, the refractive index of the single-lens fθ lens, the distance from the front principal point of the single-lens fθ lens to the deflecting surface of the deflector, and the single-lens fθ lens The distance from the front principal point to the natural convergence point of the convergent light flux is also set appropriately.

[0008]

With the above structure, distortion and field curvature in the main scanning direction can be corrected well. Moreover, single-lens fθ
The surface shape of the lens is simple, which is advantageous in lens processing.

[0009]

EXAMPLES Examples of the present invention will be described below. FIG. 1 shows the configuration of a scanning device to which the present invention is applied. In this scanning device, the light beam emitted from the light source unit 1 is made into a convergent light beam through the optical member 2 and then enters the deflecting surface of the deflector (polygon mirror) 3. The convergent light beam deflected at a constant angular velocity by the rotating polygon mirror-3 passes through the single-lens f.theta. Lens 4, is imaged on the surface 5 to be scanned, and scans the surface to be scanned at substantially constant velocity. The moving direction of the light beam (light spot on the surface to be scanned) accompanying the rotation of the deflector is called the main scanning direction, and the direction orthogonal to this main scanning direction is called the sub-scanning direction.

The first to sixth embodiments will be described below. As shown in FIGS. 2 and 3, the single-lens fθ lens 4 in each embodiment is located between the deflecting surface of the polygon mirror 3 and the surface to be scanned 5 and is a biconvex lens in the main scanning direction.

[0011] Single lens fθ lens 4 in the first embodiment the first embodiment, the first
A main curve in the main scanning direction of the surface and the second surface (a curve parallel to the main scanning direction and along the lens surface passing through the apex of the lens surface) is formed by a circle. The curvatures of the first surface and the second surface in the main scanning direction may be constant throughout. With this configuration, the surface shape in the main scanning direction can be simplified.

In the first embodiment, the following conditional expressions (1) to (3) are satisfied. (1) 0.7 ≦ d ₁ / d ₃ ≦ 1.3 (2) 0.4 <| R _1H | / | R _2H | (3) −3.5 <(nf _H / t) + (f _H / S) where R _1H is the radius of curvature of the first surface of the single lens fθ lens 4 in the main scanning direction, R _2H is the radius of curvature of the second surface of the single lens fθ lens 4 in the main scanning direction, and d ₁ is the deflector 3 The distance between the deflecting surface (corresponding to the entrance pupil) and the first surface of the single-lens fθ lens 4, d ₃ is the distance between the second surface of the single-lens fθ lens 4 and the surface to be scanned 5, and n is the refraction of the single-lens fθ lens 4. , F _H is the focal length of the single-lens fθ lens 4 in the main scanning direction, and t is the deflector 3 from the front principal point H of the single-lens fθ lens 4.
And s is the distance from the front principal point H of the single-lens fθ lens 4 to the natural convergence point of the convergent light beam (convergence point of the convergent light beam without the lens 4) P.

Conditional expression (1) is a condition for correcting field curvature and distortion aberration in the main scanning direction. When d ₁ is made smaller than d ₃ , negative distortion aberration increases, and convex convex field curvature in the main scanning direction (as the angle of view in the main scanning direction increases,
The curvature of field such that the image plane position in the main scanning direction is on the deflector side increases. If d ₁ is made larger than d ₃ , positive distortion aberration increases, and concave concave image plane in the main scanning direction (as the angle of view in the main scanning direction increases, the image plane position in the main scanning direction is scanned). The curvature of field as on the surface side increases. Therefore, if the lower limit of conditional expression (1) is exceeded, negative distortion and convex field curvature in the main scanning direction cannot be corrected, and if the upper limit is exceeded, positive distortion and concave field curvature in the main scanning direction are corrected. I can't run out.

Conditional expression (2) is also a condition for correcting field curvature and distortion in the main scanning direction. At d ₁ / d ₃ that satisfies the conditional expression (1), negative distortion occurs when R _1H is reduced. Therefore, if the lower limit of conditional expression (2) is exceeded, negative distortion cannot be completely corrected.

Conditional expression (3) is also a condition for correcting field curvature and distortion in the main scanning direction. By satisfying the conditional expression (3), not only a lens material having a high refractive index but also a plastic having a low refractive index of 1.6 or less can be used as the lens material.

The single-lens fθ lens 4 of the first embodiment is also used.
In the state where the field curvature and the distortion in the main scanning direction are properly corrected, the convex field curvature in the sub scanning direction (as the field angle in the main scanning direction increases, the image plane position in the sub scanning direction becomes closer to the deflector side). A certain field curvature) occurs. When this correction is required, at least one surface of the single-lens fθ lens 4 may be formed as a deformed toric surface whose radius of curvature in the sub-scanning direction increases as the angle of view in the main scanning direction increases. Further, it is advantageous in lens processing if only one surface of the single-lens fθ lens 4 is a modified toric surface and the other surface is a spherical surface.

[0017] Single lens fθ lens 4 in the second embodiment the second embodiment, the first
The main curves in the main scanning direction of the surface and the second surface are formed by circles. The curvatures of the first surface and the second surface in the main scanning direction may be constant throughout. With this configuration, the surface shape in the main scanning direction can be simplified.

Further, in the second embodiment, a single lens fθ
It is intended for the case where the refractive index of the lens 4 is 1.6 or less, and in addition to the conditional expression (1) described in the first embodiment, (4) 0.3 <d ₃ / f _H <0.5 Conditional expression (4) is satisfied.

Conditional expression (4) is a condition for correcting distortion. If the lower limit of conditional expression (4) is exceeded, negative distortion cannot be corrected, and if the upper limit is exceeded, positive distortion cannot be corrected.

Also in the second embodiment, as in the first embodiment, when correction of the field curvature in the sub-scanning direction is required, at least one surface of the single-lens fθ lens 4 is main-scanned. It may be formed by a deformed toric surface in which the radius of curvature in the sub-scanning direction increases as the direction angle of view increases. Further, it is advantageous in lens processing if only one surface of the single-lens fθ lens 4 is a modified toric surface and the other surface is a spherical surface.

The single lens fθ lens 4 in the third embodiment the third embodiment, the main scanning direction main curve of at least one surface is formed with a curve radius of curvature increases as increases the main scanning direction angle It Further, the curvature of at least one surface in the main scanning direction may be reduced as a whole in the main scanning direction. The single-lens fθ lens 4 may be formed in this manner on either one or both of the first surface and the second surface. With such a configuration, even when the single-lens fθ lens 4 is arranged at a position where d ₁ is smaller than d ₃ , that is, a position on the deflector 3 side, field curvature and distortion in the main scanning direction are improved. Can be corrected. That is, as d ₁ is made smaller than d ₃ , negative distortion aberration increases and convex convex field-of-field curvature increases. In order to correct this, if the radius of curvature of the single-lens fθ lens 4 in the main scanning direction is increased and the focal length of the single-lens fθ lens 4 is shifted in the direction of increasing the length, the distortion can be corrected. The field curvature in the main scanning direction cannot be corrected. Therefore, by forming the main scanning direction main curve of at least one surface of the single-lens fθ lens 4 with a curve whose curvature radius increases as the main scanning direction angle of view increases, the angle of view in the main scanning direction increases. As the power decreases, the image surface shifts to the plus side.

In the third embodiment, (5) 0.5 ≦ d ₁ / d ₃ ≦ 1.0 (6) −3.5 <(nf _H / t) + (f _H / s) Expressions (5) and (6) are satisfied.

Conditional expression (5) is a condition for correcting the field curvature in the main scanning direction, and the upper limit thereof is the above-mentioned d ₁ is d ₃
The precondition that the single-lens fθ lens 4 is arranged at a position smaller than is shown. If the lower limit of conditional expression (5) is exceeded, the field curvature in the main scanning direction cannot be completely corrected.

Conditional expression (6) is a condition for correcting field curvature and distortion in the main scanning direction. Further, by satisfying the conditional expression (6), it is possible to use a plastic having a low refractive index of 1.6 or less as a lens material.

Further, in order to satisfactorily correct field curvature and distortion in the main scanning direction, it is desirable to satisfy the following conditional expression (7). (7) 0.6 <| R _1H | / | R _2H | <0.8 If the lower limit of this conditional expression (7) is exceeded, negative distortion will increase, and if it exceeds the upper limit, negative distortion will increase. As a result, the convex field curvature is insufficiently corrected.

Also in the third embodiment, as in the above-described embodiments, when correction of the field curvature in the sub-scanning direction is required, at least one surface of the single-lens f.theta. It may be formed by a deformed toric surface whose radius of curvature in the sub-scanning direction increases as the angle of view increases. Further, it is advantageous in lens processing if only one surface of the single-lens fθ lens 4 is a modified toric surface and the other surface is a spherical surface.

The single lens fθ lens 4 in the fourth embodiment The fourth embodiment, the third
Similar to the embodiment, the main scanning direction main curve of at least one of the surfaces is formed by a curve whose radius of curvature increases as the main scanning direction angle of view increases. Further, the curvature of at least one surface in the main scanning direction may be reduced as a whole in the main scanning direction.
It should be noted that the above-mentioned formation is performed by the first lens of the single-lens fθ lens 4.
Either one or both of the surface and the second surface may be used.

Furthermore, in the fourth embodiment, a single lens fθ
It is intended for the case where the refractive index of the lens 4 is 1.6 or less, and in addition to the conditional expression (5) described in the third embodiment, (8) 0.3 <d ₃ / f _H <0.5 Conditional expression (8) is satisfied.

Conditional expression (8) is a condition for correcting distortion. If the lower limit of conditional expression (8) is exceeded, negative distortion cannot be corrected, and if the upper limit is exceeded, positive distortion cannot be corrected.

Further, in the single-lens fθ lens 4 of the fourth embodiment, the first surface thereof is a spherical surface, and the second surface thereof is an aspherical surface whose radius of curvature in the main scanning direction increases as the angle of view in the main scanning direction increases. If so, the configuration can be simplified.

Also in the fourth embodiment, like the third embodiment, the conditional expression (7) is satisfied in order to more favorably correct the field curvature and the distortion aberration in the main scanning direction. Is desirable.

Further, also in the fourth embodiment, when correction of the field curvature in the sub-scanning direction is required, at least one surface of the single-lens fθ lens 4 is imaged in the main-scanning direction in the same manner as the above-described embodiments. It may be formed by a deformed toric surface whose radius of curvature in the sub-scanning direction increases as the angle increases. Further, it is advantageous in lens processing if only one surface of the single-lens fθ lens 4 is a modified toric surface and the other surface is a spherical surface.

The single lens fθ lens 4 in the fifth embodiment The fifth embodiment, the main scanning direction main curve of at least one surface is formed with a curve radius of curvature becomes smaller as increases the main scanning direction angle It Further, the curvature of at least one surface in the main scanning direction may be increased as the angle of view in the main scanning direction is increased. The single-lens fθ lens 4 may be formed in this manner on either one or both of the first surface and the second surface. With this configuration, even when the single-lens fθ lens 4 is arranged at the position where d ₁ is larger than d ₃ , that is, the position on the scanned surface 5 side, the field curvature and the distortion aberration in the main scanning direction are good. Can be corrected to. That is, when d ₁ is made larger than d ₃ , positive distortion aberration increases, and concave main scanning direction field curvature increases. In order to correct this, if the radius of curvature of the single-lens fθ lens 4 in the main scanning direction is made smaller and the focal length of the single-lens fθ lens 4 is shifted to a shorter direction, the distortion can be corrected. The field curvature in the main scanning direction cannot be corrected. Therefore, by forming the main-scanning-direction main curve of at least one surface of the single-lens fθ lens 4 with a curve whose radius of curvature decreases as the main-scanning-direction angle of view increases, the angle of view in the main-scanning direction increases. As the power increases, the image surface shifts to the negative side.

In the fifth embodiment, (9) 1.0 ≦ d ₁ / d ₃ ≦ 2.0 (10) −3.5 <(nf _H / t) + (f _H / s) Expressions (9) and (10) are satisfied.

Conditional expression (9) is a condition for correcting the field curvature in the main scanning direction, and the lower limit thereof is the above-mentioned d ₁ is d ₃
The precondition that the single-lens fθ lens 4 is arranged at a position larger than is shown. If the upper limit of conditional expression (9) is exceeded, the curvature of field in the main scanning direction cannot be completely corrected.

Conditional expression (10) is a condition for correcting field curvature and distortion in the main scanning direction. Further, by satisfying the conditional expression (10), a plastic having a low refractive index of 1.6 or less can be used as a lens material.

Further, in order to satisfactorily correct field curvature and distortion in the main scanning direction, it is desirable to satisfy the following conditional expression (11). (11) 0.6 <| R _1H | / | R _2H | <0.8 If the lower limit of this conditional expression (11) is exceeded, negative distortion will increase, and if it exceeds the upper limit, negative distortion will increase. As a result, the convex field curvature is insufficiently corrected.

Also in the fifth embodiment, when correction of the curvature of field in the sub-scanning direction is required, at least one surface of the single-lens f.theta. It may be formed by a deformed toric surface whose radius of curvature in the sub-scanning direction increases as the angle of view increases. Further, it is advantageous in lens processing if only one surface of the single-lens fθ lens 4 is a modified toric surface and the other surface is a spherical surface.

The single lens fθ lens 4 in the sixth embodiment to the sixth embodiment, the fifth
Similar to the embodiment, the main scanning direction main curve of at least one of the surfaces is formed by a curve whose radius of curvature decreases as the main scanning direction view angle increases. Further, the curvature of at least one surface in the main scanning direction may be increased as the angle of view in the main scanning direction is increased.
It should be noted that the above-mentioned formation is performed by the first lens of the single-lens fθ lens 4.
Either one or both of the surface and the second surface may be used.

Further, in the sixth embodiment, a single lens fθ
This is intended for the case where the refractive index of the lens 4 is 1.6 or less, and in addition to the conditional expression (9) described in the fifth embodiment, (12) 0.3 <d ₃ / f _H <0.5. Conditional expression (12) is satisfied.

Conditional expression (12) is a condition for correcting distortion. If the lower limit of conditional expression (12) is exceeded, negative distortion cannot be corrected, and if the upper limit is exceeded, positive distortion cannot be corrected.

Further, in the single-lens fθ lens 4 of the sixth embodiment, the first surface thereof is a spherical surface, and the second surface thereof is an aspherical surface whose radius of curvature in the main scanning direction becomes smaller as the angle of view in the main scanning direction becomes larger. If so, the configuration can be simplified.

Also in the sixth embodiment, like the fifth embodiment, the conditional expression (11) is satisfied in order to more favorably correct the field curvature and the distortion aberration in the main scanning direction. Is desirable.

Further, also in the sixth embodiment, when correction of the curvature of field in the sub-scanning direction is required, at least one surface of the single-lens fθ lens 4 is imaged in the main-scanning direction in the same manner as in the above-described embodiments. It may be formed by a deformed toric surface whose radius of curvature in the sub-scanning direction increases as the angle increases. Further, it is advantageous in lens processing if only one surface of the single-lens fθ lens 4 is a modified toric surface and the other surface is a spherical surface.

Specific configuration examples 1 to 8 will be shown below. In each configuration example, d ₁ is the distance between the deflecting surface of the deflector 3 and the first surface of the single-lens fθ lens 4, d ₂ is the distance between the first and second surfaces of the single-lens fθ lens 4, and d ₃ is the single distance. The distance between the second surface of the ball fθ lens 4 and the surface to be scanned 5, R _1H is the radius of curvature of the first surface of the single-lens fθ lens 4 in the main scanning direction (on the optical axis), and R _2H is the single-lens fθ lens 4
Of the second surface in the main scanning direction (on the optical axis), R _1G is the radius of curvature of the first surface of the single-lens fθ lens 4 in the sub-scanning direction (on the optical axis), and R _2G is the single-lens fθ lens 4 Radius of curvature of the two surfaces in the sub-scanning direction (on the optical axis), n is the refractive index of the single-lens fθ lens 4, and f
_H is the focal length of the single-lens fθ lens 4 in the main scanning direction, t is the distance from the front principal point H of the single-lens fθ lens 4 to the deflection surface of the deflector 3, and s is the front principal point H of the single-lens fθ lens 4. The distance to the natural convergence point P of the convergent light beam, s ₁ is the distance from the deflection surface of the deflector 3 to the natural convergence point P of the convergent light beam.

When the aspherical surface (including the modified toric surface) is used as the surface of the single-lens fθ lens 4, the shape of the aspherical surface is x = [ky ² / {1+ (1-k ² y ² ) ^1/2}] + ρ + A where, k = κ / (1- κρ) ρ = cz 2 / {1+ (1-c 2 z 2) 1/2} A = a 22 y 2 z 2 + a 04 y 4 + A ₂₄ y ² z ⁴ However, x: optical axis direction coordinate from lens surface apex y: main scanning direction coordinate from lens surface apex z: sub scanning direction coordinate from lens surface apex 1 / c: profile curve radius of curvature ( Radius of curvature on optical axis in sub-scanning direction 1 / κ: Curvature radius of vertex of main curved surface (radius of curvature on optical axis in main scanning direction) a ₂₂ , a ₀₄ , a ₂₄ : aspherical coefficient 4).

[Structure example 1: Corresponding to the first and second embodiments]
In Configuration Example 1, the first surface of the single-lens fθ lens is a spherical surface and the second surface is a deformed toric surface. d ₁ = 165 d ₂ = 15 d ₃
= 165 R _1H = 420 R _2H = -510 R _1G = 420 R _2G = -54.5 a ₂₂ = 1.5 × 10 ^-7 a ₀₄ = 0 a ₂₄
= 0 n = 1.5722 f _H = 405 t = -169.3 s = 299 s _{1
= 468.3 d 1 / d 3 =} 1 | R 1H | / | R 2H | = 0.82 (nf H / t) + (f H /s)=-2.4 d 3 / f H = 0. 41 The radius of curvature in the sub-scanning direction of the deformed toric surface with respect to the angle of view (deg) in the main scanning direction is as follows. Angle of view in main scanning direction Radius of curvature in sub scanning direction +0 -54.5 +12 -55.6 +24 -59.7 An aberration diagram of this configuration example 1 is shown in FIG. In each aberration diagram, the horizontal axis represents the angle of view (deg).

[Structure example 2: Corresponding to the first and second embodiments]
In this configuration example 2, the first surface of the single-lens fθ lens is a spherical surface and the second surface is a deformed toric surface. d ₁ = 155 d ₂ = 15 d ₃
= 175 R _1H = 450 R _2H = -480 R _1G = 450 R _2G = -54.0 a ₂₂ = 1.65 × 10 ^-7 a ₀₄ = 0 a ₂₄
= 0 n = 1.5722 f _H = 408.3 t = -159.6 s = 324.4 s _{1
= 484.4 d 1 / d 3 =} 0.89 | R 1H | / | R 2H | = 0.94 (nf H / t) + (f H /s)=-2.8 d 3 / f H = 0.43 The radius of curvature in the sub-scanning direction of the deformed toric surface with respect to the angle of view (deg) in the main scanning direction is as follows. Angle of view in main scanning direction Radius of curvature in sub scanning direction + 0-54.0 +12 -55.0 +24 -58.9 An aberration diagram of this configuration example 2 is shown in FIG.

[Structure example 3: Corresponding to the first and second embodiments]
In this configuration example 3, the first surface of the single-lens fθ lens is a spherical surface and the second surface is a deformed toric surface. d ₁ = 175 d ₂ = 15 d ₃
= 155 R _1H = 400 R _2H = -520 R _1G = 400 R _2G = -54.3 a ₂₂ = 1.4 × 10 ^-7 a ₀₄ = 0 a ₂₄
= 0 n = 1.5722 f _H = 397.5 t = -179.2 s = 269.6 s _{1
= 448.8 d 1 / d 3 =} 1.13 | R 1H | / | R 2H | = 0.77 (nf H / t) + (f H /s)=-2.0 d 3 / f H = 0.39 The radius of curvature of the deformed toric surface in the sub-scanning direction with respect to the angle of view (deg) in the main scanning direction is as follows. Main scanning direction view angle Sub-scanning direction curvature radius + 0-54.3 +12 -55.7 +24 -60.4 An aberration diagram of this configuration example 3 is shown in FIG.

[Structure Example 4: Corresponding to First and Second Embodiments]
In this configuration example 4, the first surface of the single-lens fθ lens is a spherical surface and the second surface is a deformed toric surface. d ₁ = 130 d ₂ = 20 d ₃
= 130 R _1H = 330 R _2H = -580 R _1G = 330 R _2G = -43.5 a ₂₂ = 2.7 × 10 ⁻⁷ a ₀₄ = 0 a ₂₄
= 0 n = 1.5722 f _H = 370.5 t = −134.7 s = 224.1 s _{1
= 358.8 d 1 / d 3 =} 1 | R 1H | / | R 2H | = 0.57 (nf H / t) + (f H /s)=-2.7 d 3 / f H = 0. 35 The radius of curvature in the sub-scanning direction of the deformed toric surface with respect to the angle of view (deg) in the main scanning direction is as follows. Angle of view in main scanning direction Curvature radius in sub-scanning direction +0 -43.5 +15 -44.9 +30 -51.2 FIG.

[Structure Example 5: Corresponding to Third and Fourth Embodiments]
In this configuration example 5, the first surface of the single-lens fθ lens is a spherical surface and the second surface is a deformed toric surface. Also, the second
The curvature of the main curve in the main scanning direction changes depending on the angle of view in the main scanning direction. d ₁ = 150 d ₂ = 15 d ₃
= 180 R _1H = 405 R _2H = −550 R _1G = 405 R _2G = −54.4 a ₂₂ = 1.82 × 10 ⁻⁷ a ₀₄ = 3.0 × 10 ⁻⁹ a ₂₄
= 0 n = 1.5722 f _H = 410.0 t = -154 s = 339.8 s _{1
= 493.8 d 1 / d 3 =} 0.83 | R 1H | / | R 2H | = 0.74 (nf H / t) + (f H /s)=-2.98 d 3 / f H = 0.44 The radius of curvature of the modified toric surface in the main scanning direction and the sub scanning direction with respect to the angle of view (deg) in the main scanning direction is as follows. Angle of view in main scanning direction Radius of curvature in main scanning direction Curvature radius in sub-scanning direction +0 -550.0 -54.4 +12 -55.5 +24 -608.1 -59.9 An aberration diagram of this configuration example 5 is shown in FIG. Show.

[Structure example 6: Corresponding to the fifth and sixth embodiments]
In this configuration example 6, the first surface of the single-lens fθ lens is a spherical surface, and the second surface is a deformed toric surface. Also, the second
The curvature of the main curve in the main scanning direction changes depending on the angle of view in the main scanning direction. d ₁ = 200 d ₂ = 25 d
₃ = 120 R _1H = 355 R _2H = −500 R _1G = 355 R _2G = −50.0 a ₂₂ = 1.40 × 10 ⁻⁷ a ₀₄ = −1.8 × 10 ⁻⁹ a
₂₄ = 0 n = 1.5722 f _H = 366.7 t = −206.7 s = 202.9 s
_{1 = 409.6 d 1 / d 3} = 1.7 | R 1H | / | R 2H | = 0.71 (nf H / t) + (f H /s)=-1.0 d 3 / f H = 0.33 The main scanning direction and sub-scanning direction radii of curvature of the modified toric surface with respect to the main scanning direction angle of view (deg) are as follows. Angle of view in main scanning direction Radius of curvature in main scanning direction Curvature radius in sub-scanning direction +0 -500.0 -50.0 +12 -51.2 +24 4588.8 -56.2 The aberration diagram of this configuration example 6 is shown in FIG. Show.

[Structure Example 7: Corresponding to Third and Fourth Embodiments]
In the configuration example 7, the first surface of the single-lens fθ lens is a spherical surface and the second surface is a deformed toric surface. Also, the second
The curvature of the main curve in the main scanning direction changes depending on the angle of view in the main scanning direction. d ₁ = 125 d ₂ = 15 d
₃ = 150 R _1H = 350 R _2H = −550 R _1G = 350 R _2G = −45.4 a ₂₂ = 3.0 × 10 ⁻⁹ a ₀₄ = 2.5 × 10 ⁻⁹ a
_{24 = 0 n = 1.5722 f H} = 376.0 t = -128.7 s = 271.3 s
_{1 = 400.0 d 1 / d 3} = 0.84 | R 1H | / | R 2H | = 0.64 (nf H / t) + (f H /s)=-3.2 d 3 / f H = 0.40 The radius of curvature of the modified toric surface in the main scanning direction and the sub scanning direction with respect to the angle of view (deg) in the main scanning direction is as follows. Angle of view in main scanning direction Curvature radius in main scanning direction Curvature radius in sub-scanning direction +0 −550.0 −45.4 +14 −560.2 −46.7 +28 −598.7 −52.3 Aberration diagram of this configuration example 7 Is shown in FIG.

[Structure Example 8: Corresponding to Second Embodiment] In Structure Example 8, the first surface of the single-lens fθ lens is a modified toric surface, and the second surface is a spherical surface. d ₁ = 70 d ₂ = 30 d ₃
= 108.36 R _1H = 250 R _2H = -500 R _1G = 26.9 R _2G = -500 a ₂₂ = 3.35 × 10 ^-6 a ₀₄ = 0 a ₂₄
= 3.6 × 10 ⁻¹⁰ n = 1.5722 f _H = 295.564 t = −76.454 s = 219.729 s _{1
= 296.183 d 1 / d 3 =} 0.646 | R 1H | / | R 2H | = 0.5 (nf H / t) + (f H /s)=-4.724 d 3 / f H = 0.367 The radius of curvature of the deformed toric surface in the sub-scanning direction with respect to the angle of view (deg) in the main scanning direction is as follows. Angle of view in main scanning direction Radius of curvature in sub-scanning direction +0 26.9 +12 27.963 +14 28.378 +24 31.989 +28 34.434 +38 42.827 An aberration diagram of the configuration example 8 is shown in FIG.

[0055]

As is apparent from the above description, according to the present invention, it is possible to provide a scanning device in which distortion and field curvature in the main scanning direction are properly corrected. Moreover, the surface shape of the single-lens fθ lens is simple, which is advantageous in lens processing.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a scanning device to which the present invention is applied.

FIG. 2 is a top view showing a main part of a scanning device according to an embodiment.

FIG. 3 is a side view showing a main part of the scanning device according to the embodiment.

FIG. 4 is an explanatory diagram for defining the shape of a modified toric surface.

FIG. 5 is an aberration diagram in Configuration Example 1.

FIG. 6 is an aberration diagram in Configuration Example 2.

FIG. 7 is an aberration diagram in Configuration Example 3.

FIG. 8 is an aberration diagram in Configuration Example 4.

FIG. 9 is an aberration diagram in Configuration Example 5.

FIG. 10 is an aberration diagram in Configuration Example 6.

FIG. 11 is an aberration diagram in Configuration Example 7.

FIG. 12 is an aberration diagram in Configuration Example 8.

[Explanation of symbols]

 1 light source 2 optical member 3 deflector 4 single lens fθ lens 5 surface to be scanned

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Osamu Ono 2-3-13 Azuchi-cho, Chuo-ku, Osaka Osaka International Building Minolta Camera Co., Ltd.

Claims (11)

[Claims] 1. A scanning device comprising a deflector, wherein a convergent light beam deflected at a constant angular velocity by the deflector is imaged on a surface to be scanned, and the surface to be scanned is scanned at substantially the same speed. , A single-lens fθ lens located between the deflector and the surface to be scanned, the single-lens fθ lens being a biconvex lens in the main-scanning direction, and a main-curving direction main curve of the first and second surfaces thereof. Is formed by a circle and satisfies the following condition: 0.7 ≦ d ₁ / d ₃ ≦ 1.3 0.4 <| R _1H | / | R _2H | −3 .5 <(nf _H / t) + (f _H / s) where R _{1H is the} radius of curvature of the first surface of the single-lens fθ lens in the main scanning direction R _{2H is the} radius of curvature of the second surface of the single-lens fθ lens Radius of curvature d ₁ : Distance between deflecting surface of deflector and first surface of single-lens fθ lens d ₃ : Distance between second surface of single-lens fθ lens and scanned surface n: Single-lens Refractive index of fθ lens f _H : Focal length of single-lens fθ lens in main scanning direction t: Distance from front principal point of single-lens fθ lens to deflecting surface of deflector s: Convergent light flux from front-side principal point of single-lens fθ lens The distance to the natural convergence point of. 2. A scanning device which comprises a deflector, forms an image of a convergent light beam deflected at a constant angular velocity by the deflector on a surface to be scanned, and scans the surface to be scanned at a substantially constant velocity. A single-lens fθ lens located between the deflector and the surface to be scanned, the single-lens fθ lens being a biconvex lens in the main scanning direction made of a material having a refractive index of 1.6 or less. 1
A main scanning direction main curve of the first surface and the second surface is formed by a circle, and the scanning device is characterized by satisfying the following conditions: 0.7 ≦ d ₁ / d ₃ ≦ 1.3 0.3 < d ₃ / f _H <0.5, where d ₁ : distance between deflecting surface of deflector and first surface of single-lens fθ lens d ₃ : distance between second surface of single-lens fθ lens and surface to be scanned f _H : Focal length of single lens fθ lens in main scanning direction. 3. A scanning device comprising a deflector, wherein a convergent light beam deflected at a constant angular velocity by the deflector is imaged on a surface to be scanned, and the surface to be scanned is scanned at a substantially constant speed. A single-lens fθ lens located between the deflector and the surface to be scanned, the single-lens fθ lens being a biconvex lens in the main-scanning direction, and a main-curving direction main curve of at least one of the surfaces being the main-scanning direction. The scanning device is formed by a curve whose radius of curvature increases as the direction angle of view increases, and which satisfies the following conditions: 0.5 ≦ d ₁ / d ₃ ≦ 1.0 −3.5 <(Nf _H / t) + (f _H / s) where d ₁ is the distance between the deflecting surface of the deflector and the first surface of the single-lens fθ lens d ₃ : The second surface of the single-lens fθ lens and the surface to be scanned interval n of refractive index f _H of the single lens fθ lens: main scanning direction focal length of the single lens fθ lens t: single lens Distance s from the front principal point of θ lens to the deflecting surface of the deflector distance from the front principal point of the single lens fθ lens to the natural converging point of the convergent light beam. 4. A scanning device comprising a deflector, wherein a convergent light beam deflected at a constant angular velocity by the deflector is imaged on a surface to be scanned, and the surface to be scanned is scanned at a substantially constant speed. A single-lens fθ lens located between the deflector and the surface to be scanned, the single-lens fθ lens being made of a material having a refractive index of 1.6 or less and being a biconvex lens in the main scanning direction; The main scanning direction main curve of one surface is formed by a curve whose curvature radius increases as the main scanning direction angle of view increases, and the following condition is satisfied: 0.5 ≦ d ₁ / d ₃ ≦ 1.0 0.3 <d ₃ / f _H <0.5 where d ₁ is the distance between the deflecting surface of the deflector and the first surface of the single-lens fθ lens d ₃ : The single-lens fθ lens Distance between second surface and surface to be scanned f _H : Focal length of single-lens fθ lens in main scanning direction. 5. The first surface of the single-lens fθ lens is formed as a spherical surface, and the second surface is formed as an aspherical surface whose radius of curvature in the main scanning direction increases as the angle of view in the main scanning direction increases. The scanning device according to claim 4, wherein: 6. A scanning device comprising a deflector, wherein a convergent light beam deflected at a constant angular velocity by the deflector is imaged on a surface to be scanned and the surface to be scanned is scanned at substantially the same speed. A single-lens fθ lens located between the deflector and the surface to be scanned, the single-lens fθ lens being a biconvex lens in the main-scanning direction, and a main-curving direction main curve of at least one of the surfaces being the main-scanning direction. The scanning device is formed by a curve whose curvature radius decreases as the direction angle of view increases, and the following conditions are satisfied: 1.0 ≦ d ₁ / d ₃ ≦ 2.0 −3.5 <(Nf _H / t) + (f _H / s) where d ₁ is the distance between the deflecting surface of the deflector and the first surface of the single-lens fθ lens d ₃ : The second surface of the single-lens fθ lens and the surface to be scanned interval n of refractive index f _H of the single lens fθ lens: main scanning direction focal length of the single lens fθ lens t: single lens Distance s from the front principal point of θ lens to the deflecting surface of the deflector distance from the front principal point of the single lens fθ lens to the natural converging point of the convergent light beam. 7. A scanning device comprising a deflector, wherein a convergent light beam deflected at a constant angular velocity by the deflector is imaged on a surface to be scanned and the surface to be scanned is scanned at substantially the same speed. A single-lens fθ lens located between the deflector and the surface to be scanned, the single-lens fθ lens being made of a material having a refractive index of 1.6 or less and being a biconvex lens in the main scanning direction; The main scanning direction main curve of one surface is formed by a curve whose curvature radius decreases as the main scanning direction angle of view increases, and the following conditions are satisfied: A scanning device: 1.0 ≦ d ₁ / d ₃ ≦ 2.0 0.3 <d ₃ / f _H <0.5 where d ₁ is the distance between the deflecting surface of the deflector and the first surface of the single-lens fθ lens d ₃ : The single-lens fθ lens Distance between second surface and surface to be scanned f _H : Focal length of single-lens fθ lens in main scanning direction. 8. The first surface of the single-lens fθ lens is formed as a spherical surface, and the second surface is formed as an aspherical surface whose radius of curvature in the main scanning direction decreases as the angle of view in the main scanning direction increases. The scanning device according to claim 7, wherein: 9. A modified toric surface in which at least one surface of the single-lens fθ lens has a radius of curvature in the sub-scanning direction that increases as the angle of view in the main scanning direction increases. Claim 1 or Claim 2 or Claim 3
Alternatively, the scanning device according to claim 4, claim 6, or claim 7. 10. The scanning device according to claim 9, wherein one surface of the single-lens fθ lens is formed as a spherical surface, and the other surface is formed as the modified toric surface. 11. A scanning device according to claim 3, characterized in that the following conditions are satisfied: 0.6 <| R _1H | / | R _2H | <0.8 where R _{1H is the} radius of curvature of the first surface of the single-lens fθ lens in the main scanning direction R _{2H is the} radius of curvature of the second surface of the single-lens fθ lens in the main scanning direction.