JP3210790B2 - Optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used as an optical writing device in a laser printer, a laser facsimile, a laser copying machine or the like.

[0002]

2. Description of the Related Art A light beam from a light source device such as a laser light source is deflected and scanned at a constant angular velocity by an optical deflector such as a rotary polygon mirror.
There have been proposed various optical scanning devices that perform optical scanning by converging a light spot on a surface to be scanned such as a photoreceptor or the like by a constant-speed scanning image forming optical element, such as a laser printer, a laser facsimile, and a laser copying machine. It is used as an optical writing device in machines and the like. In such an optical scanning device, an fθ lens has been widely known as an optical element for condensing a deflected light beam as a light spot on a surface to be scanned, but a reflective imaging element ( An optical element having a function of reflecting a deflected light beam and condensing it as a light spot on a surface to be scanned, which is referred to as an image-forming reflecting mirror for constant-speed scanning or an fθ mirror, has been proposed. (Japanese Patent Publication No. 55-36127,
4-123040, JP-A-2-84612, JP-A-1-200219).

In an optical scanning apparatus using such an imaging mirror for constant-speed scanning, a deflected light beam deflected by an optical deflector such as a rotary polygon mirror is directed to the optical deflector by the imaging mirror for constant-speed scanning. Since the optical path is folded back, an optical path separating unit that separates an optical path from the optical deflector to the imaging mirror for constant-speed scanning and an optical path from the imaging mirror for constant-speed scanning to the surface to be scanned is required. As one of the optical path separating means, for example, a light beam is incident from a direction inclined with respect to the rotation axis of the deflecting reflection surface in the optical deflector, and the direction of the deflection light beam is inclined from a plane orthogonal to the rotation axis. It is possible. By doing so, the direction of the deflected light beam incident on the imaging mirror for constant-speed scanning and the direction of the reflected light beam are separated, so that the optical path of the incident deflected light beam and the optical path of the reflected light beam can be separated. However, when the optical path is separated by such means, in order to make the layout of each optical element possible, the angle of the incident light beam with respect to the deflecting / reflecting surface must be increased to some extent. The locus of the light spot on the scanning surface, that is, a large bend in the scanning line, hinders good scanning.

In general, a rotary polygon mirror is used as an optical deflector, but the position of a reflection point shifts with the rotation of the rotary polygon mirror, so that a reflection point variation generally called a sag occurs, and an image plane is degraded. A phenomenon called rotation occurs. When an fθ lens is used as an image forming system, Japanese Patent Laid-Open No. 1-9271
As disclosed in Japanese Patent Application Laid-Open No. 7-342, and Japanese Patent Application Laid-Open No. 4-342222, the correction can be made by shifting the fθ lens in parallel with the medium to be scanned. When a mirror is used, the above means cannot completely correct the rotation of the image plane.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and uses an optical deflector such as a rotary polygonal mirror for deflection scanning, and uses a reflecting mirror as an imaging optical element for uniform scanning. In the case of using, the rotation of the image plane can be easily corrected,
It is another object of the present invention to provide a novel optical scanning device provided with a unit capable of effectively correcting the bending of the scanning line.

[0006]

According to a first aspect of the present invention, there is provided an optical scanning device, comprising: a light source device; and a light beam from the light source device, the light beam corresponding to a sub-scanning direction (an optical path from the light source to the surface to be scanned). Are converged in a virtual optical path linearly developed along the optical axis in a direction corresponding to the sub-scanning direction (in a direction corresponding to the sub-scanning direction), and the optical path from the light source to the surface to be scanned is shifted along the optical axis. An optical element that forms a line image that is long in a virtual optical path that is linearly developed along the main scanning direction (in a direction corresponding to the main scanning direction), and a deflecting reflective surface near the image forming position of the line image. A light deflector for deflecting a light beam at a constant angular velocity, and a light beam deflected by the light deflector is condensed as a light spot on a surface to be scanned, and the light spot is arranged to scan the surface to be scanned at a constant speed. With an optical system having a fixed imaging mirror for constant velocity scanning The above-mentioned imaging mirror for constant velocity scanning is tilted with a straight line passing through a point where an optical axis intersects a straight line orthogonal to the deflection scanning plane (main scanning plane) and orthogonal to the deflection scanning plane as a rotation axis. (The optical axis of the imaging mirror for constant-speed scanning is inclined with respect to the optical axis of the optical system.) Note that the deflection scanning surface is
A virtual plane (main scanning plane) formed by sweeping the principal ray of the deflected light beam ideally deflected by the optical deflector. For example, when the optical deflector is a rotary polygon mirror, the rotation of the rotary polygon mirror It becomes a plane orthogonal to the axis.

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the imaging mirror for constant-speed scanning passes through a point where an optical axis thereof intersects a straight line orthogonal to the deflection scanning surface. It is characterized by being arranged obliquely about a straight line orthogonal to the deflection scanning surface as a rotation axis, and displaced in the direction parallel to the surface to be scanned within the deflection scanning surface.

According to a third aspect of the present invention, in the optical scanning device of the first aspect, the imaging mirror for constant-speed scanning passes through a point where an optical axis thereof intersects a straight line orthogonal to the deflection scanning surface. It is characterized by being arranged obliquely about a straight line orthogonal to the deflection scanning surface as a rotation axis, and further displaced in a direction orthogonal to the deflection scanning surface.

The optical scanning device according to the fourth aspect is the first aspect.
In the optical scanning device described, the imaging reflector for constant-speed scanning,
An axis that is inclined with a rotation axis passing through a point where the optical axis intersects a straight line orthogonal to the deflection scanning surface and that is orthogonal to the deflection scanning surface, and that is parallel to the deflection scanning surface and orthogonal to the optical axis of the optical system. Are arranged to be inclined with respect to the rotation center.

According to a fifth aspect of the present invention, in the optical scanning device of the third aspect, the imaging mirror for constant-speed scanning is further displaced in a direction parallel to the surface to be scanned in the deflection scanning surface. It is characterized by having been done.

According to a sixth aspect of the present invention, there is provided the optical scanning device according to the fourth aspect, wherein the imaging mirror for constant-speed scanning is further parallel to the deflection scanning surface and orthogonal to the optical axis of the optical system. , And are arranged so as to be shifted from each other.

According to a seventh aspect of the present invention, in the optical scanning device according to the first aspect, the imaging mirror for constant-speed scanning passes through a point where an optical axis thereof intersects a straight line orthogonal to the deflection scanning surface. It is arranged to be inclined with a straight line perpendicular to the deflection scanning surface as a rotation axis, further shifted in a direction parallel to the surface to be scanned within the deflection scanning surface, and further shifted in a direction orthogonal to the deflection scanning surface. Further, it is characterized in that it is arranged to be inclined about an axis parallel to the deflection scanning surface and orthogonal to the optical axis of the optical system as a rotation center.

[0013]

In the optical scanning apparatus according to the present invention, the image-forming reflecting mirror for constant-speed scanning is formed such that a rotation axis is a straight line passing through a point where the optical axis intersects a straight line orthogonal to the deflection scanning surface and orthogonal to the deflection scanning surface. The tilted arrangement makes it possible to correct the rotation of the image plane, which is a problem when a rotating polygon mirror or the like is used as the optical deflector. Further, in the optical scanning device according to the second aspect, the image-forming mirror for constant-speed scanning is further displaced in a direction parallel to the surface to be scanned in the deflection scanning surface, thereby rotating the image surface. Correction can be easily performed.

Further, in the optical scanning apparatus according to the third to seventh aspects, the imaging mirror for constant-speed scanning is arranged so that the mirror is perpendicular to the deflection scanning surface through a point where the optical axis intersects a straight line orthogonal to the deflection scanning surface. To be tilted as a rotation axis, and further displaced in a direction parallel to the surface to be scanned within the deflection scanning surface, or further displaced in a direction orthogonal to the deflection scanning surface, or When a rotating polygon mirror or the like is used as an optical deflector by arranging it at an angle parallel to the deflection scanning surface and orthogonal to the optical axis of the optical system, or by using a combination of these. In this case, it is possible to correct the rotation of the image plane, which is a problem, and to effectively correct the curvature of the scanning line, which is the locus of the light spot.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a perspective view showing a schematic configuration of a scanning optical system in the optical scanning device of the present invention. In FIG. 1, reference numeral 1 denotes a light source device, which in this example is a semiconductor laser (LD), which emits a divergent light beam. In addition, an LED or the like can be used as the light source device.
After the light beam from the light source device 1 passes through the condenser lens 2, main scanning is performed by a latent image forming optical element (such as a cylindrical lens having power in the sub-scanning direction) 3 having power to converge only in the sub-scanning corresponding direction. A line image long in the corresponding direction is formed near the deflection reflection surface 4A of the optical deflector 4. In the illustrated example, the light deflector 4 is a rotary polygon mirror having a plurality of deflecting / reflecting surfaces 4A parallel to the rotation axis. The incoming light beam is deflected at a constant angular velocity by the deflecting / reflecting surface 4A. A virtual plane (main scanning plane) formed by sweeping the principal ray of the deflected light beam ideally deflected by the optical deflector 4 is a deflection scanning surface. In this example, the rotation axis of the rotary polygon mirror is used. Is a plane orthogonal to.

The light beam deflected at a constant angular velocity by the light deflector 4 is incident on and reflected by a constant-speed scanning image forming reflecting mirror 6, and then is returned by a return mirror (or a half mirror) 5 to form a photosensitive member. Are condensed as light spots on the medium 7 to be scanned and optically scan the medium 7 to be scanned. That is, the light spot optically scans the optical scanning line L on the medium 7 to be scanned according to the deflection of the light beam due to the rotation of the optical deflector 4. The surface to be scanned includes the tangent plane on the peripheral surface of the medium to be scanned 7 that includes the optical scanning line L. Reference numeral 11 in the figure denotes a surface tilt correction optical element in the sub-scanning direction.

In this example, as shown in FIG. 2 (b), the constant-speed scanning image forming mirror 6 does not return the reflected light to the optical deflector 4 side. Image reflector 6
Is slightly tilted with respect to the incident light beam. But,
As shown in FIG. 2A, the configuration may be such that the light reflected by the constant-speed scanning imaging reflecting mirror 6 directly scans the medium 7 to be scanned, or when there is a margin in the amount of light, As shown in FIG. 2C, the reflected light beam may be reflected by a semi-transmissive mirror (half mirror) 8 and guided to the medium 7 to be scanned, without tilting the imaging mirror for constant-speed scanning 6. Various other optical path configurations are also possible. When the imaging mirror for constant-speed scanning 6 is tilted, the scanning line is bent. However, the present applicant has previously filed Japanese Patent Application Nos. 4-62522 and 4-254.
No. 60080, etc., a half mirror or a parallel plate inserted in the optical path of the deflected light beam is tilted,
As will be described later, the bending of the scanning line can be reduced to a level that does not substantially cause a problem by shifting the imaging mirror for constant-speed scanning 6.

Next, a description will be given of the imaging mirror for constant-speed scanning. The constant-speed scanning imaging reflecting mirror 6 has a function of condensing the deflected light beam onto a light spot on the surface to be scanned, and also makes the light scanning by the light spot substantially uniform (the deviation of the light spot from the constant-speed scanning). To the extent that it is not necessary to correct optical scanning errors due to electrical signal processing).

The shape of the constant-speed scanning imaging reflector 6 is perpendicular to the optical axis of the constant-speed scanning imaging reflector 6 (the axis of symmetry of the mirror surface) and parallel to the main scanning direction. Within the plane determined by the straight line (referred to as the principal symmetry plane), the mirror surface of the imaging mirror for constant-speed scanning 6 has a coordinate in the optical axis direction of X and an origin in the optical axis position. coordinate as Y, ^{formula, X = Y 2 / {R} m + √ (R m 2 - (1 + K) Y 2)} + a 2 Y 2 + a 3
Y ³ + A ₄ Y ⁴ +... (R _m : radius of curvature on the optical axis, K: conical constant, A ₂ , A ₃ , A
₄ ...: aspherical coefficient). Accordingly, the mirror surface shape of the constant-speed scanning imaging reflecting mirror 6 is R _m , R _s ,
It is determined by three parameters, K. The fact that the mirror surface of the imaging mirror 6 for constant-speed scanning has the shape represented by the above general formula means that the shape of the mirror surface is substantially represented by the above general formula.

In general, a rotary polygon mirror is used as the optical deflector 4. However, since the position of the reflection point shifts with the rotation of the rotary polygon mirror, a variation in the reflection point, which is generally called sag, occurs. The phenomenon occurs. When an fθ lens is used as an imaging system, as disclosed in JP-A-1-92717 and JP-A-4-342222,
The correction can be made by shifting the fθ lens in parallel with the medium to be scanned. However, when an imaging reflecting mirror for constant-speed scanning is used in the imaging system, the above-described means can completely correct the rotation of the image plane. Can not. According to the present invention, the rotation of the image plane is determined by using a constant-speed scanning imaging reflecting mirror 6 as a straight line passing through the point where the optical axis intersects a straight line orthogonal to the deflection scanning plane (main scanning plane) and orthogonal to the deflection scanning plane. Is to be corrected by tilting the rotation axis.

FIG. 3 is a view for explaining an embodiment of the present invention, and is a view virtually showing an optical system arrangement and an optical path on a main scanning plane of a scanning optical system. Hereinafter, the correcting means of the present invention will be described with reference to FIG. In the deflection scanning plane (main scanning plane), when the light beam incident on the deflection reflection surface 4A of the optical deflector is convergent light, the light from the imaging mirror for constant-speed scanning 6 to the natural focal point of the convergent light beam Let the distance be S ₀ . When the light beam incident on the deflecting / reflecting surface 4A of the optical deflector is a divergent light beam, the position of the imaginary light source of the incident light beam corresponds to the natural condensing point, and the position of the imaginary light source is the position of the imaging mirror for constant speed scanning 6. It is located in front of the mirror surface, is represented by a negative distance, and is represented by the symbol S ₀ as in the case of the convergent light flux. Further, the thickness of the line image forming optical element 3 is d ₂ , the refractive index is n, the radius of curvature on the light source side is R _1M (main scanning direction), R _1S (sub scanning direction), and the radius of curvature on the optical deflector side. _Are R _2M (main scanning direction) and R _2S (sub scanning direction), and the distance between the line image forming element 3 and the deflecting / reflecting surface 4A is d.
_3, and the deflection angle of the optical deflector 4 is θ.

In FIG. 3, in the present invention, the imaging mirror for constant-speed scanning 6 passes through the point where the optical axis intersects a straight line perpendicular to the deflection scanning plane (main scanning plane) and is orthogonal to the deflection scanning plane. They are arranged to be inclined (rotated) with the straight line as the rotation axis S, and the rotated angle (tilt angle) is γ. That is, by appropriately adjusting the tilt angle γ, the rotation of the image plane can be corrected. Further, in FIG. 3, when the main optical axis direction of the optical system in the deflection scanning plane is an x direction, and a direction orthogonal to the x direction and parallel to the scanning surface 7 ′ of the medium to be scanned is a y direction, Even if the imaging mirror for constant-speed scanning 6 is displaced (shifted) in a direction (y-direction) parallel to the surface 7 'to be scanned, the rotation of the image plane can be corrected. By performing both the rotation of the imaging mirror 6 about the rotation axis S and the shift in the y direction, the rotation of the image plane can be more effectively corrected.

Next, FIG. 4 is a view for explaining another embodiment of the present invention, in which the arrangement of the optical system after the optical deflector and the optical path of the scanning optical system are shown in a cross section in the sub-scanning direction. It is.
In this embodiment, a sub-cylindrical mirror 80 having power only in the sub-scanning direction is used as the surface tilt correction optical system. In addition, as shown in FIG. 4, a half mirror 50 is used to separate the light beam. In this embodiment, the surface 5b of the half mirror 50 on the side of the constant-speed scanning imaging reflecting mirror 6 is a reflecting surface (half surface). (Mirror surface). Reference symbol BS denotes a virtual plane formed by sweeping the principal ray of the deflected light beam ideally deflected by the optical deflector 4, that is, a deflection scanning plane (main scanning plane). The half mirror 50 is arranged to be inclined with respect to the deflection scanning surface BS,
The deflected light beam from the optical deflector 4 passes through the half mirror 50, is reflected by the imaging mirror for constant-speed scanning 6, is reflected by the reflection surface 5 b of the half mirror 50, and is further reflected by the sub-cylindrical mirror 80. The light is condensed on the medium to be scanned 7 as a light spot.

By the way, as shown in FIG.
When a half mirror 50 for separating a light beam is provided between the image forming reflecting mirror 6 for scanning at a constant speed and the half mirror 50 is disposed at an angle with respect to the deflection scanning surface, the half mirror 50 becomes thick due to the thickness of the half mirror 50. The deflected light beam transmitted through the mirror 50 is shifted in a direction orthogonal to the deflected scanning surface BS. For this reason,
If the optical axis of the constant-speed scanning imaging reflector 6 is aligned with the deflection scanning surface, the incident position of the deflected light beam on the constant-speed scanning imaging reflector 6 deviates from the optical axis, and this is the light spot. Of the trajectory (scanning line). Therefore, in this embodiment, in FIG. 4, the direction parallel to the rotation axis of the optical deflector 4 is the z-axis, and the imaging reflection for constant velocity scanning is performed in a plane (deflection scanning plane) orthogonal to the rotation axis of the optical deflector 4. Assuming that the direction parallel to the optical axis AX of the mirror 6 is the x axis, the imaging mirror for constant velocity scanning 6 is moved in the direction (z
Direction). By doing so, it is possible to effectively correct the bending of the scanning line. In addition, in addition to the above, it is also possible to correct the scanning line bending by disposing the optical axis AX of the imaging mirror for constant-speed scanning 6 at an angle to the deflection scanning surface BS.

In the optical scanning device according to the present invention, as shown in FIG. 3, the rotation of the imaging mirror for constant velocity scanning 6 around the rotation axis S and the shift in the y direction cause the image plane to be shifted. The rotation can be effectively corrected, and as shown in FIG. 4, the imaging mirror for constant-speed scanning 6 is shifted (shifted) in a direction (z direction) orthogonal to the deflection scanning surface BS. ) To dispose or set the optical axis AX of the imaging mirror for constant-speed scanning 6 to the deflection scanning plane B.
By arranging the scanning line at an angle to S, it is possible to effectively correct the bending of the scanning line. Therefore, by implementing the correction means described with reference to FIGS. 3 and 4, it is possible to provide an optical scanning device in which both the rotation of the image plane and the curvature of the scanning line are corrected.

Next, the effects of the present invention will be described with reference to specific examples. (Embodiment 1) The configuration of the optical system after the optical deflector 4 of the optical scanning device is the same as that of FIG. 4, the direction parallel to the rotation axis of the optical deflector 4 is the z axis, and the rotation axis of the optical deflector 4 is When the direction parallel to the optical axis AX of the imaging mirror for constant-speed scanning 6 in the orthogonal plane (deflection scanning plane) is the x-axis, the plane orthogonal to the rotation axis of the optical deflector 4 (deflection scanning plane). Imaging reflector 6 for uniform scanning from BS
Is the shift amount of the optical axis AX in the z direction. Also,
The angle between the incident light beam and the reflected light beam of the sub-cylindrical mirror 80 is represented by β. In FIG. 4, α is an angle formed between the half mirror 50 and the incident light beam, and it is assumed that the light beam incident on the half mirror 50 and the optical axis AX of the imaging mirror for constant-speed scanning 6 are set in parallel. I do. Then, as shown in FIG. 3, the constant-speed scanning imaging reflecting mirror 6 passes through a point where its optical axis AX intersects with a straight line orthogonal to the deflection scanning plane (main scanning plane) BS and is orthogonal to the deflection scanning plane BS. Is inclined with respect to the rotation axis S, and the angle rotated about the rotation axis S is γ. Note that γ is a counterclockwise direction in the + direction.

The refractive index of the half mirror 50 is n ′,
The distance from the deflecting / reflecting surface 4A of the optical deflector 4 to the light incident surface of the half mirror 50 is d ₀ , the distance from the light incident point to the light emitting point of the half mirror 50 is d ₁ , and the distance from the light emitting point of the half mirror 50 The distance from the reflecting surface of the imaging mirror 6 for fast scanning is d ₄ , and the distance between the deflection scanning surface BS and the sub-cylindrical mirror 80 is
The distance to the reflecting surface of d ₅ , the secondary cylindrical mirror 8
0 is the distance from the reflecting surface of the scanning medium 7 to the scanning surface of the medium 7 to be scanned.
_{6 is} assumed. The radius of curvature of the sub cylindrical mirror 80 is R _3M (main scanning direction) and R _3S (sub scanning direction).
The arrangement of the optical system before the light deflector 4 is the same as that of FIG. 3, and the thickness of the line image forming optical element 3 is d ₂ , the refractive index is n, and the radius of curvature on the light source side is R _1M (in the main scanning direction). ), R _1S (sub-scanning direction), radius of curvature on the optical deflector 4 side as R _2M (main scanning direction),
R _2S (sub-scanning direction), the distance between the linear image forming element 3 and the deflecting / reflecting surface 4A is d _3, and the deflection angle of the optical deflector 4 is θ.

Specific numerical values of each parameter in the present embodiment are summarized below. R _1M = ∞, R _1S = 96.11 mm, R _2M = ∞, R _2S = ∞
, R _3M = ∞, R _3S = -143.46 mm, d ₂ = 5 mm, n
= 1.51118, d ₃ = 146.852 mm, d ₀ = 254.921 mm,
_{d 1 = 7.071mm, n '=} 1.51118, d 4 = 18.336mm
, D ₅ = 81.664 mm, R = −800.0 mm, K = 0.5, A ₄
= 1.0 × 10 ~ ¹⁰ , A ₆ = -2.8 × 10 ~ ¹⁵ , A ₈ = 2.6 × 10 ~ ²⁰
, S ₀ = 595.674 mm, θ = ± 28.4 °, α = 45 °, β = 1
0 °, γ = -2.328 °, Δz = 8.336mm, Δy = -34.15mm
, Δ = 0.

Here, Δy represents the shift amount when the imaging mirror for constant-speed scanning 6 is shifted in the direction parallel to the surface to be scanned (the y direction in FIG. 3). That is, in the present embodiment, both the shift in the y direction of the imaging mirror for constant-speed scanning 6 and the rotation about the rotation axis S are performed, and the rotation of the image plane is corrected by these effects. . Further, in this embodiment, the curvature of the scanning line is corrected by shifting the imaging mirror for constant-speed scanning 6 in the z direction. FIG. 5A shows an aberration diagram in the optical scanning device of the present embodiment. In the aberration diagrams, the field curvature indicates the dynamic field curvature when the optical deflector rotates, and the dotted line indicates the imaging performance in the main scanning direction and the solid line indicates the imaging performance in the sub-scanning direction. In linearity and fθ characteristics,
The dotted line indicates the fθ characteristic, the solid line indicates the linearity, and f
As is well known, the θ characteristic indicates that the ideal image height is H _r (θ) and the actual image height is H _i (H _i ).
When (θ) is defined, (fθ characteristic) = {H _r (θ) / H _i (θ) −1} × 100 (%). Also, the linearity is well known like the fθ characteristics, as defined in _{(linearity) = {dH r (θ)} / dH i (θ) -1} × 100 (%).

Next, for comparison, an example is shown in which both the shift in the y-direction of the imaging mirror for constant-speed scanning 6 and the rotation about the rotation axis S are not performed. Numerical data of each parameter of the comparative example in this case were set to the same conditions except that γ = 0 ° and Δy = 0. The aberration diagram at this time is shown in FIG.
(B). Comparing (a) and (b) of FIG.
(A) has improved field curvature, fθ characteristics, and linearity, and the effect of the present invention is clear. Note that γ =
Needless to say, the performance is not achieved only by shifting in the y direction, as in 0 °, Δy = -34.5.

(Embodiment 2) Next, the curvature of the scanning line is corrected without using the shift in the z-direction in FIG. Means for tilting (rotating) around a straight line orthogonal to the optical axis AX (FIG. 4)
An example is shown in which correction is made by using the angle .theta. Note that δ is a clockwise direction in the + direction. Specific numerical values of each parameter in the present embodiment are summarized below. R _1M = ∞, R _1S = 96.11 mm, R _2M = ∞, R _2S = ∞
, R _3M = ∞, R _3S = -143.46 mm, d ₂ = 5 mm, n
= 1.51118, d ₃ = 146.852 mm, d ₀ = 254.921 mm,
d ₁ = 7.071 mm, n ′ = 1.51118, d ₄ = 18.336 mm,
_{d 5 = 81.664mm, R = -800.0mm} , K = 0.5, A 4 =
1.0 × 10 ~ ¹⁰ , A ₆ = -2.8 × 10 ~ ¹⁵ , A ₈ = 2.6 × 10 ~
²⁰ , S ₀ = 595.674 mm, θ = ± 28.4 °, α = 45 °, β
= 10 °, γ = -2.328 °, Δz = 0, Δy = -34.15mm
, Δ = 0.6 °.

FIG. 6 shows aberration diagrams in the optical scanning device of this embodiment. As is apparent from FIG. 6, also in this embodiment, the field curvature, the fθ characteristic, and the linearity are improved, and the scanning line bending is also effectively corrected.

[0033]

As described above, in the optical scanning apparatus according to the first aspect, an optical deflector such as a rotary polygon mirror is used for deflection scanning, and a reflecting mirror is used for an imaging optical element for uniform scanning. Also in this case, the imaging mirror for constant velocity scanning is arranged so that a straight line passing through a point where the optical axis intersects a straight line orthogonal to the deflection scanning plane (main scanning plane) and orthogonal to the deflection scanning plane is used as a rotation axis. This makes it possible to easily correct the rotation of the image plane.

In the optical scanning apparatus according to the second aspect, the imaging mirror for constant-speed scanning is formed by rotating a straight line orthogonal to the deflection scanning surface through a point where an optical axis thereof intersects a straight line orthogonal to the deflection scanning surface. By tilting and displacing in the direction parallel to the surface to be scanned in the deflection scanning plane, the mutual effect of rotation and shift of the imaging mirror for constant velocity scanning,
The rotation of the image plane can be easily corrected.

According to a third aspect of the present invention, in the optical scanning apparatus, the imaging mirror for constant-speed scanning is formed by rotating a straight line perpendicular to the deflection scanning surface through a point where an optical axis intersects a straight line orthogonal to the deflection scanning surface. By arranging them at an angle and further displacing them in a direction orthogonal to the deflection scanning plane, both the rotation of the image plane and the bending of the scanning line can be effectively corrected.

In the optical scanning device according to the fourth aspect, the imaging mirror for constant-speed scanning is formed by rotating a straight line perpendicular to the deflection scanning surface through a point where an optical axis intersects a straight line orthogonal to the deflection scanning surface. By tilting the axis of rotation about the axis parallel to the deflection scanning surface and orthogonal to the optical axis of the optical system, both the rotation of the image plane and the bending of the scanning line are effectively corrected. be able to.

According to a fifth aspect of the present invention, in the optical scanning device of the third aspect, the imaging mirror for constant-speed scanning is further displaced in a direction parallel to the surface to be scanned within the deflection scanning surface. Accordingly, the rotation of the image plane can be more easily corrected and the curvature of the scanning line can be effectively corrected by the mutual effect of the rotation and the shift of the imaging reflector for constant velocity scanning. .

In the optical scanning device according to the sixth aspect, in the optical scanning device according to the fourth aspect, the imaging mirror for constant-speed scanning further has a direction parallel to the deflection scanning surface and perpendicular to the optical axis of the optical system. By being shifted, the rotation of the image plane can be more easily corrected, and the curvature of the scanning line can be effectively corrected.

In the optical scanning device of the present invention, the imaging mirror for constant-speed scanning is configured such that a rotation axis is a straight line passing through a point where an optical axis intersects a straight line orthogonal to the deflection scanning surface and orthogonal to the deflection scanning surface. Are arranged in a tilted manner, further shifted in a direction parallel to the surface to be scanned within the deflection scanning surface, further shifted in a direction orthogonal to the deflection scanning surface, and further parallel to the deflection scanning surface. By being tilted around the axis orthogonal to the optical axis of the optical system as the center of rotation,
The rotation of the image plane can be more easily corrected, and the curvature of the scanning line can be more effectively corrected.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration example of a scanning optical system in an optical scanning device of the present invention.

FIG. 2 is an explanatory diagram of an optical path in a sub-scanning direction of an optical scanning device to which the present invention is applied.

FIG. 3 is a diagram for explaining an embodiment of the present invention,
FIG. 3 is a diagram virtually illustrating an optical system arrangement and an optical path on a main scanning plane of the scanning optical system.

FIG. 4 is a diagram for explaining another embodiment of the present invention, and is a diagram showing an optical system arrangement and an optical path after an optical deflector of a scanning optical system in a cross section in the sub-scanning direction.

FIG. 5 is an explanatory diagram of a correction effect according to the present invention,
FIG. 3A is a diagram illustrating aberrations in the optical scanning device according to the first embodiment.
FIG. 7B is a diagram illustrating aberrations when the rotation of the image plane is not corrected.

FIG. 6 is an explanatory diagram of a correction effect according to the present invention, showing aberrations in the optical scanning device according to the second embodiment.

[Description of Signs] 1: Light source device 2: Condensing lens 3: Line image forming optical element 4: Optical deflector (rotating polygon mirror) 4A: Deflective reflecting surface 5: Return mirror 6: Image forming reflection for constant speed scanning Mirror 7: Scanned medium 8, 50: Half mirror 11: Surface tilt correction optical element 80: Sub-cylindrical mirror

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-348310 (JP, A) JP-A-56-167118 (JP, A) JP-A-2-308213 (JP, A) JP-A-5-167 346549 (JP, A) JP-A-1-200221 (JP, A) JP-A-5-45598 (JP, A) JP-A-64-52116 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 26/10

Claims (7)

(57) [Claims] 1. A light source device, an optical element for converging a light beam from the light source device in a sub-scanning corresponding direction to form a line image long in a main scanning corresponding direction, and deflecting and reflecting near an image forming position of the line image A light deflector having a surface and deflecting a light beam at a constant angular velocity; and a light beam deflected by the light deflector is condensed as a light spot on a surface to be scanned, and the light spot is used to scan the surface to be scanned at a constant speed. In an optical scanning device provided with an optical system having an arranged constant-speed scanning imaging reflector, the constant-speed scanning imaging reflector is orthogonal to its optical axis and a deflection scanning plane (main scanning plane). The optical axis of the imaging mirror for constant-speed scanning is tilted with respect to the optical axis of the optical system, and is inclined with respect to the optical axis of the optical system. Optical scanning device. 2. The optical scanning device according to claim 1, wherein the imaging mirror for constant-speed scanning forms a straight line orthogonal to the deflection scanning surface through a point where the optical axis intersects a straight line orthogonal to the deflection scanning surface. An optical scanning device, wherein the optical scanning device is arranged to be inclined as a rotation axis and is shifted in a direction parallel to a surface to be scanned within a deflection scanning surface. 3. The optical scanning device according to claim 1, wherein the imaging mirror for constant-speed scanning forms a straight line orthogonal to the deflection scanning surface through a point at which the optical axis intersects a straight line orthogonal to the deflection scanning surface. An optical scanning device, wherein the optical scanning device is arranged to be tilted as a rotation axis and further shifted in a direction orthogonal to a deflection scanning surface. 4. The optical scanning device according to claim 1, wherein the imaging mirror for constant-speed scanning forms a straight line orthogonal to the deflection scanning surface through a point where the optical axis intersects a straight line orthogonal to the deflection scanning surface. An optical scanning device, wherein the optical scanning device is tilted as a rotation axis, and further tilted with an axis parallel to the deflection scanning surface and orthogonal to the optical axis of the optical system as a rotation center. 5. The optical scanning device according to claim 3, wherein the imaging mirror for constant-speed scanning is further displaced in a direction parallel to the surface to be scanned in the deflection scanning surface. Optical scanning device. 6. The optical scanning device according to claim 4, wherein the imaging mirror for constant-speed scanning is further displaced in a direction parallel to the deflection scanning surface and orthogonal to the optical axis of the optical system. An optical scanning device characterized by the above-mentioned. 7. The optical scanning device according to claim 1, wherein the imaging mirror for constant-speed scanning forms a straight line orthogonal to the deflection scanning surface through a point at which the optical axis intersects a straight line orthogonal to the deflection scanning surface. It is disposed at an angle as a rotation axis, is further displaced in a direction parallel to the surface to be scanned within the deflection scanning surface, is further displaced in a direction orthogonal to the deflection scanning surface, and further includes a deflection scanning surface. An optical scanning device, wherein the optical scanning device is arranged to be inclined about an axis parallel to and orthogonal to an optical axis of an optical system as a rotation center.