JPH08211319A - Light deflector and optical scanner - Google Patents

Abstract

PURPOSE: To relax required precision for the error of the radius of an inscribed circle and to reduce an irregular amount of a dot position in a scanning end on a surface to be scanned by making a shape of a reflection surface in the direction of a main scanning into a non-circular arc and enlarging a radius of curvature of a vertex in the direction of the main scanning larger than a prescribed value obtained by specified calculation. CONSTITUTION: An optical scanner is constituted of a light source 1, an incident lens system 2 and a slit 3, a light deflector 4 provided with plural reflection surfaces 4A-4D, a cylindrical mirror 5 and a photoreceptor 6. At this time, the reflection surfaces 4A-4D are respectively constituted of a projecting aspherical surface provided with a projecting non-circular arc shape in the direction of the main scanning, and provided with a linear shape in the direction of a sub-scanning having no refractive power. Then, when a distance from a deflection point in a deflection angle 0 deg. to the surface to be scanned is defined L, and the distance from the scanning center of the surface to be scanned to an effective scanning end Y, the radius of curvature R of the vertex in the direction of the main scanning is provided with the relation of R>41.1(Y<3> / L<2> )-34.9(Y<2> /L)+9.7Y.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical deflector and an optical scanning device applied to a digital copying machine, a laser printer, etc., and more particularly, while having a function of correcting field curvature.
The present invention relates to an optical deflector and an optical scanning device which suppress the unevenness of dot positions at the scanning end on the surface to be scanned and also reduce the accuracy of the inscribed circle radius error to reduce the cost.

[0002]

2. Description of the Related Art As an optical scanning device applied to a digital copying machine, a laser printer, or the like, a light beam modulated according to an image signal is reflected and deflected by a reflection type optical deflector, for example, a polygon mirror, and a photoconductor or the like. In general, there is known one in which image information is recorded by scanning the surface to be scanned.

By the way, in the above optical scanning device, in order to correct the field curvature and focus the light beam on the surface to be scanned over the entire scanning area, the light beam is deflected at a constant angular velocity by the reflection type deflector. A scanning lens (fθ lens) is provided after the optical deflector in order to intentionally distort and scan the surface to be scanned at a constant speed.

However, in order to be able to cover all the deflected light flux with this scanning lens, the scanning lens must be made large, and in addition, a highly accurate one is required to satisfy the above requirements. It has the disadvantage of being expensive.

Therefore, recently, an optical deflector for correcting the field curvature without using a scanning lens, that is, for focusing a light beam on a surface to be scanned over the entire scanning region is disclosed in, for example, Japanese Patent Laid-Open No. It is proposed by Japanese Patent Laid-Open No. 61-156020.

In the above-mentioned optical deflector, the reflecting surface is composed of a convex spherical surface or a cylindrical surface having a refractive power. That is,
By making the reflecting surface a convex spherical surface or a cylindrical surface, the refractive power of the reflecting surface becomes weaker from the apex in the main scanning direction toward both ends, and the focus position becomes farther toward the scanning end and the image plane becomes flat. It is trying to make it. Further, Japanese Patent Application Laid-Open No. 1-116515 proposes that the reflecting surface is a convex aspherical surface represented by a higher-order curve, which can further correct the field curvature.

By the way, since the shape accuracy of the optical deflector influences the image quality, the accuracy required for the shape error becomes strict.

FIG. 7 shows the influence of the shape error on the image quality. When there is a shape error in the main scanning corresponding direction on the reflecting surface, the scanning characteristic in the main scanning direction changes, so that the dot generation position on the scanning surface changes. To do. As a result, image expansion / contraction (change in magnification) occurs within one line, and dot position misalignment (jitter) in a plurality of lines repeats at a cycle of the number of reflecting surfaces (4 cycles in the figure). appear.
Here, the absolute amount of the shape error influences the change of the magnification, and the difference in the shape between the plurality of reflecting surfaces affects the jitter, but the jitter is recognized in the image quality even if the deviation is about 1/2 of the dot diameter. On the other hand, since the magnification is difficult to recognize even if it changes by several times the dot diameter, the required accuracy for the variation of the shape error between the surfaces is more severe than the absolute amount of the shape error in the optical deflector having a plurality of reflecting surfaces. Become.

8A, 8B, and 8C are convex reflection surfaces 4
3 shows the shape error of the optical polarizer 4 with A to 4D. (a) is a lateral deviation eccentricity in which the deflection reflection surface 4A is 4A 'and is displaced in the main scanning direction, (b) is a rotation eccentricity in which the deflection reflection surface 4A is 4A' and is displaced in the rotation direction, and (c) is a deflection reflection surface. 4A is 4
A'indicates the radius error of the inscribed circle that is displaced in the incoming and outgoing directions of the light flux.
This is the radius error of the inscribed circle in (c). This is related to the synchronous control of the image writing start position. That is, the influence of the lateral deviation eccentricity and the rotational eccentricity is alleviated by controlling the writing position, whereas the inscribed circle radius error increases.

FIG. 9 shows the relationship between the radius error of the inscribed circle of the flat reflecting surface and the scanning distance. When the radius of the inscribed circle of the reflecting surface 8 is Rp, the optical deflector rotates by 2α about the rotation axis O, thereby deflecting by 4α, and the range S0 on the surface 9 to be scanned is scanned.
Are scanned. On the other hand, the radius of the inscribed circle of the reflecting surface 8 is Δ
When Rp increases, the deflection range 4α does not change,
Since the distance to the surface to be scanned 9 is shortened by the amount of extension of the reflecting surface 8 ′, the scanning is performed in the range S1 (<S0).
When the image writing start position is synchronously controlled in this state, the image writing starts from the same position P as when the inscribed circle radius is Rp, and the range S2 is scanned over the deflection angle of 4α. As a result, the difference ΔRp in the radius of the inscribed circle between the plurality of reflecting surfaces
, The dot positions S0-S2 (= ΔS) are not aligned at the end of scanning.

FIG. 10 shows the relationship between the inscribed circle radius error of the convex reflecting surface and the scanning position. The distance from the rotation axis O of the optical deflector to the surface 9 to be scanned does not change, and the reflecting surface 4A is 4A. Consider the change in the scanning range when the radius of the inscribed circle of the optical polarizer is increased by ΔRp after the displacement to '. At this time, the scanning position Y changes from Y0 to Y1 as the convex reflecting surface moves out by ΔRp, as in the case of the planar reflecting surface, but when the reflecting surface is convex, the normal direction of the convex reflecting surface. Changes from θ to θ ′, the scanning position further moves to Y2. As a result, when there is a difference ΔRp in the radius of the inscribed circle between the convex reflecting surfaces, if the scanning start position is synchronously controlled, the dot position is larger by (Y1−Y2) × 2 at the scanning end than in the case of the planar reflecting surface. Irregularity occurs.

As described above, in the optical deflector having a convex reflecting surface, there is a strict requirement for the accuracy of the shape error, in particular, the error of the radius of the inscribed circle. It was confirmed that the radius error of the inscribed circle must be in the range of 0.01 to 0.02 mm in order to reach the level where it is difficult to recognize the unevenness of the dot positions at the scanning end on the surface to be scanned in terms of image quality. There is.

[0013]

However, according to the conventional optical polarizer, in order to suppress the unevenness of the dot position at the scanning end on the surface to be scanned, the accuracy of the parts, especially the accuracy required for the inscribed circle radius error, is required. However, there is an inconvenience that the cost is increased because

Therefore, an object of the present invention is to suppress the unevenness of the dot position at the scanning end on the surface to be scanned while having the function of correcting the curvature of field, and to alleviate the accuracy of the inscribed circle radius error. It is an object of the present invention to provide an optical deflector that can reduce costs.

[0015]

In view of the above problems, the present invention has an inscribed circle without causing irregular dot positions at the scanning end on the surface to be scanned while having a function of correcting field curvature. In order to reduce the accuracy of the radius error and reduce costs, the reflecting surface has a convex non-arcuate shape in the main scanning direction and a linear convex aspherical shape in the sub-scanning direction that has no refractive power. When the distance from the deflection point to the surface to be scanned at a deflection angle of 0 ° is L and the distance from the scanning center of the surface to be scanned to the effective scanning end is Y, the curvature radius R of the apex in the main scanning direction is , R> 41.1 (Y ³ / L ² ) -34.9 (Y ² / L) +
An optical deflector having a relationship of 9.7Y is provided.

Further, the optical scanning device of the present invention which achieves the above object, a light source for emitting a light beam, an optical system for converting the light beam into a light beam having a predetermined width in the main scanning direction, and a light beam received from the optical system. Having a plurality of reflecting surfaces for reflecting and deflecting, the shape in the main scanning direction is a convex non-arc shape, and the shape in the sub-scanning direction is composed of a linear convex aspheric surface having no refractive power, and, When the distance from the deflection point at the deflection angle of 0 ° to the scanned surface is L and the distance from the scanning center of the scanned surface to the effective scanning end is Y, the radius of curvature R of the apex in the main scanning direction is R> 41.1 (Y ³ / L ² ) -34.9 (Y ² / L) +
An optical deflector having a relationship of 9.7Y, and an optical deflector provided between the optical deflector and the surface to be scanned, in which the reflecting surface and the surface to be scanned of the optical deflector are geometrically-optically conjugate in the sub-scanning direction. And an anamorphic optical element that guides the deflected light of the container to the surface to be scanned.

In the above-mentioned optical deflector, a difference in distance between the plurality of reflecting surfaces from the rotation axis to the reflecting surface is at least 0.02.
A configuration of a plastic polygon mirror having a size of 5 mm or more is preferable.

[0018]

The required accuracy for the inscribed circle radius error is relaxed by making the shape of the reflecting surface in the main scanning direction a non-circular arc and making the radius of curvature of the apex in the main scanning direction larger than the predetermined value obtained by the above-mentioned calculation. , The amount of misalignment of dot positions at the scanning end on the surface to be scanned is reduced. In addition, the field curvature is corrected even in a portion other than the apex of the reflecting surface, and the dot diameter on the scanning surface is made uniform.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical deflector and optical scanning device of the present invention will be described in detail below with reference to the accompanying drawings.

FIGS. 1A and 1B show an optical deflector of the present invention,
And an embodiment of an optical scanning device is shown. Here, the optical scanning device includes a light source 1 such as a semiconductor laser that emits a light beam modulated according to an image signal, an incident lens system 2 that guides the light beam emitted from the light source 1 to an optical deflector 4 described later, and An optical deflector 4 which has a slit 3 and a plurality of convex reflecting surfaces 4A to 4D having a refractive power in the main scanning direction, and which reflects and deflects a light beam incident by rotation about a rotation axis O, and an optical deflector 4
It is configured to include a cylindrical mirror 5 that reflects the deflected light of the above and guides it to the surface of the photoconductor 6, and a photoconductor 6 that is scanned by the deflected light that has entered through the cylindrical mirror 5. Dots are 7S to 7E of scan line 7
Formed across.

The incident lens system 2 is composed of a convex lens 2A and a cylindrical lens 2B. The light beam diverged from the light source 1 is converged into a light beam in the main scanning direction, and the reflection surface of the optical deflector 4 in the sub scanning direction. It is configured to form a light beam that is focused on.

The cylindrical mirror 5 has a radius of curvature such that the reflecting surfaces 4A to 4D of the optical deflector 4 and the surface of the photosensitive member 6 have a geometrical optical conjugate relationship, and the optical deflector 4 has power in the main scanning direction. It is configured to collect the deflected light from the surface of the photoconductor 6. Therefore, due to a phenomenon in which the angle formed by the rotation axis O and the normal line of the reflecting surfaces 4A to 4D of the optical deflector 4 in the sub-scanning direction varies from surface to surface, so-called surface inclination,
The writing position of the upper scanning line 7 in the sub-scanning direction is suppressed from varying for each scanning line.

Next, the optical deflector 4 will be described in detail. In the optical deflector 4, each of the reflecting surfaces 4A to 4D has a convex non-arcuate shape having a refracting power in the main scanning direction, and a linear convex aspherical shape having no refracting power in the sub-scanning direction. In addition, the curvatures of the vertices 10A to 10D of the reflecting surfaces 4A to 4D in the main scanning direction are larger than a predetermined value obtained by the following calculation.

That is, the radius of curvature of the vertices 10A to 10D of the reflecting surfaces 4A to 4D in the main scanning direction is R, the distance from the deflection point to the photoconductor 6 at a deflection angle of 0 ° is L, and the scanning center C to the effective scanning end. When the distance to 7S or 7E is Y, R> 41.1 (Y ³ / L ² ) −34.9 (Y ² / L) +
The relationship of 9.7Y is satisfied.

Such an optical deflector 4 has reflecting surfaces 4A to 4A.
Since the radius of curvature R of the vertex of D in the main scanning direction is sufficiently large, the distance from the rotation axis O of the optical deflector 4 to the plurality of reflecting surfaces 4A to 4D, that is, the radius error of the inscribed circle varies. Even if there is, it is possible to reduce the unevenness of the dot position at the scanning end on the surface to be scanned. Further, since the reflecting surfaces 4A to 4D are non-arcuate, the curvature of field is sufficiently corrected, and the dot diameter on the scanning line 7 can be made uniform.

In FIG. 1, the incident lens system 2 is replaced by a convex lens 2.
Although a combination of A and the cylindrical lens 2B is used, a single lens having an anamorphic image forming characteristic may be used. Furthermore, as an anamorphic optical element,
Instead of the cylindrical mirror 5, for example, a toroidal mirror or toroidal lens having a refractive power also in the main scanning direction, an aspherical mirror, an aspherical lens, or the like may be used to correct the constant velocity of the scanning speed.

Although the reflecting surfaces 4A to 4D of the optical deflector 4 are aspherical, they are injection-molded using a plastic material such as amorphous polyolefin or polycarbonate, and aluminum or copper is vacuum-deposited on the surface. If the reflective surface is formed by coating with, it can be manufactured at low cost. Furthermore, the reflecting surfaces 4A to 4 of the optical deflector 4 of the present embodiment.
Since D is a cylindrical aspherical surface, in the process of processing the mold component that becomes the master of the convex reflecting surface in the plastic molding die, the necessary number of reflecting surfaces are ground at the same time, By performing the polishing process, it is possible to process a plurality of reflection surface mold masters into the same shape even when a processing error occurs, and thus it is possible to suppress the unevenness of the dot positions in the sub-scanning direction.

Next, the reason why the reflecting surfaces 4A to 4D of the optical deflector 4 are constructed as described above will be explained.

FIG. 2 shows a change in the reflection characteristic when there is an inscribed circle radius error in the optical deflector having the arcuate reflecting surface 4A. Here, the radius of curvature of the reflecting surface 4A is Rf, the radius of the inscribed circle of the optical deflector is Rp, the rotation angle of the optical deflector is α, and the modulus at the reflection point a on the reflecting surface 4 when the radius of the inscribed circle is Rp. The linear direction is θ, the radius error of the inscribed circle of the optical deflector is ΔRp, and the normal direction at the reflection point a ′ on the reflecting surface 4A ′ when the radius error of the inscribed circle is ΔRp is θ ′, the rotation center of the optical deflector. O, reflective surface 4
The center of curvature of A is C, and the center of curvature of the reflecting surface 4A ′ is C ′.

When the sine theorem is applied to the triangles O, a and C, the deflection angle 2θ after reflection is obtained by sin θ = {(Rf-Rp) / Rf} sin α. On the other hand, when the radius of the inscribed circle of the optical deflector changes by ΔRp, applying the sine theorem to the triangles O, a ′, and C ′, sin θ ′ = [{Rf− (Rp + ΔRp)} / Rf] s
The deflection angle 2θ ′ after reflection is determined by inα. From this, the change in deflection angle Δθ due to the change in inscribed radius ΔRp is Δθ = 2 (θ−θ ′).

Therefore, after determining Δθ from the requirement for the image quality (the amount of non-uniformity of the dot positions) and ΔRp from the conditions that can reduce the processing accuracy, the reflecting surface 4A necessary for setting Δθ to a desired value. If the radius of curvature Rf is determined by the above equation, it is possible to provide an optical deflector that does not require strict component accuracy.

However, in the case where the shape of the reflecting surface in the main scanning direction is an arc, if the radius of curvature Rf is increased in order to reduce Δθ, an excessive negative field curvature is generated and the spot size on the scanning surface is reduced. It cannot be maintained evenly. Therefore, in the present embodiment, the shape of the reflecting surface 4A in the main scanning direction is a non-circular arc, and the vertex 1 in the main scanning direction that does not significantly affect the correction of the field curvature.
By making the radius of curvature of 0A to 10D larger than the predetermined value obtained by the above-described calculation, deterioration of image quality (unevenness of dot positions at the scanning end) is suppressed even if the accuracy required for the inscribed circle radius error is relaxed. I am trying.

FIG. 3 is a graph showing the relationship between the distance L from the deflection point at the deflection angle of 0 ° to the scanning surface and the radius of curvature R at the apex of the convex reflecting surface in the main scanning direction as a parameter of the inscribed circle radius error. Is. Here, the distance Y from the scanning center to the effective scanning end is 110 mm, and the radius of the inscribed circle is 12 m.
m is the result of calculation for an uneven amount of dot positions of 50 μm at the end of scanning. Uneven amount of dot position 50
The beam diameter of a small laser printer is about 100 μm.
Since it is on the order of μm, 1/2 of that was selected.

Further, in FIG. 3, when the shape of the reflecting surface in the main scanning direction is an arc, the distance L from the deflection point to the scanning surface at a deflection angle of 0 ° necessary to sufficiently correct the curvature of field.
And the relationship between the curvature R at the apex of the reflecting surface in the main scanning direction, and the image in the optical deflector disclosed in JP-A-61-156020 and the optical deflector disclosed in JP-A-1-116515. A distance L from the deflection point to the scanning surface at a deflection angle of 0 ° necessary to sufficiently correct the surface curvature,
The relationship of the curvature R at the apex of the reflecting surface in the main scanning direction is also shown. In the above publication, numerical values are read under the condition that the distance Y from the scanning center to the effective scanning end is 110 mm.

As can be seen from FIG. 3, as the distance L from the deflection point to the scanning surface at the deflection angle of 0 ° becomes smaller, the vertex in the main scanning direction required to secure the same allowable inscribed circle radius on the reflecting surface. Has a large radius of curvature R. That is, when the distance L from the deflection point at the deflection angle of 0 ° to the scanning surface is reduced in order to reduce the size of the optical system, the radius of curvature R of the apex of the reflecting surface in the main scanning direction must be increased inscribed. The required accuracy for the circle radius error becomes strict. When the shape of the reflecting surface in the main scanning direction is a circular arc, the inscribed circle radius error allowed is 0.01 to 0.02.
It is in the range of mm, which is very strict as the processing accuracy of an optical deflector having a non-planar reflecting surface.

Also in the optical deflector disclosed in Japanese Patent Laid-Open No. 1-116515, the radius of curvature R of the apex of the reflecting surface in the main scanning direction is an arc shape in order to correct the field curvature and the scanning non-linearity. Since the size is about the same as in the case of (1), the required accuracy for the radius error of the inscribed circle is in the range of 0.01 to 0.02 mm as shown in FIG.

From the relationship between the distance L from the deflection point at the deflection angle of 0 ° to the scanning surface and the radius of curvature R at the apex of the convex reflecting surface in the main scanning direction, the present inventors have found that the dot position is not uniform. When we examined the condition that the required accuracy for the radius error of the inscribed circle of the convex reflecting surface was loosened to 0.025 mm or more for 50 μm, the distance from the deflection point to the scanning surface at the deflection angle of 0 ° was L, and the effective distance from the scanning center was effective. when the distance to the scanning end was Y, the radius of curvature R is R> 41.1 in the main scanning direction the apex of the reflective surface ^{(Y 3 / L 2) -34.9} (Y 2 / L) +
It has been found possible by satisfying the relationship of 9.7Y.

Specific examples of the present invention will be described below. Table 1 shows specific conditions of Examples 1 to 3 that satisfy the above relational expressions.

[Table 1] The reflecting surface has coordinates Z in the normal direction at the apex in the main scanning direction, orthogonal to the Z axis, and coordinates Y in the main scanning direction.
Then, Z (Y) = a ₂ Y ² + a ₄ Y ⁴ + a ₆ Y ⁶ + a ₈ Y ⁸ +
a ₁₀ Y ¹⁰ a ₂ : Secondary count that determines the non-arc shape of the reflecting surface in the main scanning direction a ₄ : Quaternary count that determines the non-arc shape of the reflecting surface in the main scanning direction a ₆ : Main scanning of the reflecting surface It is assumed that it is represented by an equation of 6th order that determines the direction non-arc shape, and the meanings of the symbols shown in the table are as follows. L: Distance from the deflection point to the scanning surface at a deflection angle of 0 ° [mm] Y: Distance from the scanning center to the effective scanning end [mm] S: Distance from the reflecting surface to the virtual focusing point of the incident light beam [m
m] Rp: radius of the inscribed circle of the light deflector Rf: radius of curvature of the apex of the reflection surface of the light deflector in the main scanning direction [mm] (Rf1 / 2a ₂ ) Rc: radius of the inscribed circle of the convex reflection surface Calculated value of conditional expression that loosens required accuracy for error to 0.025 mm or more

FIG. 4, FIG. 5 and FIG. 6 show characteristics of field curvature in the main scanning direction corresponding to the first to third embodiments.
From these figures, it can be seen that the field curvature is corrected in each of the examples even if the required accuracy for the radius error of the inscribed circle is relaxed while suppressing the unevenness of the dot position at the scanning end on the surface to be scanned.

[0040]

As described above, according to the optical deflector of the present invention, the shape of the reflecting surface in the main scanning direction is a convex non-arcuate shape, and the distance L from the deflection point to the surface to be scanned at the deflection angle 0 °, And the radius Y of the vertex in the main scanning direction, where Y is the distance from the scanning center of the surface to be scanned to the effective scanning end.
R> 41.1 (Y ³ / L ² ) −34.9 (Y ² / L) +
Since it is set to 9.7Y, it has a function of correcting the curvature of field, while suppressing the unevenness of the dot position at the scanning end of the surface to be scanned, and further mitigating the accuracy of the inscribed circle radius error to reduce the cost. Therefore, the cost can be reduced also in the optical scanning device of the present invention.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between an inscribed circle radius error of an arcuate reflecting surface and a reflection characteristic.

FIG. 3 is a graph showing a relationship between a distance from a deflection point at a deflection angle of 0 ° to a scanning surface and a curvature radius of a vertex of a reflecting surface in a main scanning direction as a parameter of an inscribed circle radius error.

FIG. 4 is an explanatory diagram showing a field curvature characteristic in a main scanning direction of the first embodiment.

FIG. 5 is an explanatory diagram showing a field curvature characteristic in a main scanning direction of the second embodiment.

FIG. 6 is an explanatory diagram showing a field curvature characteristic in a main scanning direction according to a third embodiment.

FIG. 7 is an explanatory diagram showing the influence of the shape error of the optical deflector on the image quality.

FIG. 8 is an explanatory diagram showing a shape error of a convex reflecting surface of the optical deflector.

FIG. 9 is an explanatory diagram showing a relationship between an inscribed circle radius error and a scanning distance when a reflecting surface is a flat surface.

FIG. 10 is an explanatory diagram showing a relationship between an inscribed circle radius error of a convex reflecting surface and a scanning distance.

[Explanation of symbols]

 1 Light Source 2 Incident Lens System 2A Convex Lens 2B Cylindrical Lens 3 Slit 4 Optical Deflector 4A-4D Reflecting Surface 5 Cylindrical Mirror 6 Photoreceptor 7 Scanning Line 8 Reflecting Surface 9 Scanning Surface 10A-10D Vertex

Claims (3)

[Claims] 1. An optical deflector for reflecting and deflecting a light beam on a plurality of reflecting surfaces and scanning the surface to be scanned, wherein the reflecting surface has a convex non-arcuate shape in the main scanning direction and a sub-scanning direction. Is composed of a linear convex aspherical surface having no refractive power, the distance from the deflection point at the deflection angle of 0 ° to the scanned surface is L, and the scanning center of the scanned surface to the effective scanning end. when the distance was set to Y, the radius of curvature R of the vertices in the main scanning ^{direction, R> 41.1 (Y 3 /} L 2) -34.9 (Y 2 / L) +
An optical deflector having a relationship of 9.7Y. 2. A light source for emitting a light beam, an optical system for converting the light beam into a light beam having a predetermined width in the main scanning direction, and a plurality of reflecting surfaces for reflecting and deflecting the light beam received from the optical system. However, the shape in the main scanning direction is a convex non-arcuate shape, the shape in the sub scanning direction is composed of a linear convex aspherical surface having no refractive power, and the deflection angle is 0 °.
, L is the distance from the deflection point to the scanned surface, and Y is the distance from the scanning center of the scanned surface to the effective scanning end.
And the radius of curvature R of the apex in the main scanning direction is
^{There, R> 41.1 (Y 3 /} L 2) -34.9 (Y 2 / L) +
An optical deflector having a relationship of 9.7Y, and a geometrical-optical conjugate provided between the optical deflector and the surface to be scanned, the reflecting surface and the surface to be scanned of the optical deflector in the sub-scanning direction. Relatedly, an optical scanning device comprising: an anamorphic optical element that guides the deflected light of the optical deflector to the surface to be scanned. 3. The optical deflector is a plastic polygon mirror in which a difference in distance between the plurality of reflecting surfaces from the rotation axis to the reflecting surface is at least 0.025 mm or more. Optical scanning device.