JP2000131633A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a scanning optical device whose constitution is highly precise and also is simple. SOLUTION: A luminous flux emitted from a light source means 1 is deflected by a deflecting means 5, and the luminous flux deflected by the deflecting means 5 is guided to a surface to be scanned 7 by a scanning optical means 6, so that the surface to be scanned 7 is optically scanned. In this case, the scanning optical means 6 possesses a first optical element 6a which does not have power caused by refraction and a second optical element 6b consisting of an anamorphic lens having different positive power caused by the refraction in a horizontal scanning direction and a vertical scanning direction, and a diffraction grating 8 having the positive power caused by diffraction is formed on at least one surface of the first optical element 6a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device, and more particularly to a scanning optical device which guides a light beam (light beam) emitted from a light source means onto a surface to be scanned as a recording medium surface via an optical deflector such as a rotary polygon mirror. The present invention relates to a scanning optical device suitable for an apparatus such as a laser beam printer or a digital copier, which records light, information, and the like by illuminating the surface to be scanned with the light beam. .

[0002]

2. Description of the Related Art Conventionally, a scanning optical device used in a laser beam printer, a digital copying machine or the like deflects a light beam emitted from a light source means by a deflecting means, and covers the deflected light beam by the scanning optical means. An image is formed in the form of a spot on the photosensitive drum surface, which is the scanning surface, and the surface to be scanned is optically scanned.

FIG. 19 is a schematic view of a main part of a conventional scanning optical device. In the figure, a light beam emitted from a light source means 91 composed of a semiconductor laser or the like is converted by a collimator lens 92 into a substantially parallel light beam. The converted substantially parallel light beam is shaped into an optimal beam shape by an aperture stop 93,
The light enters the cylindrical lens 94. The cylindrical lens 94 has power in the sub-scanning direction, and forms an image as a linear light beam elongated in the main scanning direction on the vicinity of the deflection surface 95a of the optical deflector 95 composed of a rotating polygon mirror or the like. Here, the main scanning direction is a direction parallel to the deflection scanning direction, the sub-scanning direction is a direction perpendicular to the deflection scanning direction, and so on. The linear light beam is reflected and deflected at a constant angular velocity by an optical deflector 95, and is scanned by a fθ lens system having fθ characteristics as scanning optical means, that is, a photosensitive drum surface (recording medium surface) which is a surface to be scanned 97.
An image is formed on the photosensitive drum surface in a spot shape, and the surface of the photosensitive drum is optically scanned at a constant speed.

[0004]

In recent years, an fθ lens serving as a scanning optical means is often formed of a plastic material for cost reduction. In this plastic lens, the thickness of the lens greatly affects the molding time, and when the lens thickness is large, the time required for molding becomes longer,
It becomes a factor of high cost. Therefore, when using a plastic material, it is important to reduce the lens thickness as much as possible in order to reduce the cost. As a solution, for example, use of a diffractive optical element can be considered. By forming a diffraction grating on the optical element surface and changing the pitch of the diffraction grating in the main scanning direction and / or the sub-scanning direction, it is possible to converge or diverge a light beam and to have the same power as a lens. Become. Therefore, by sharing the power to the diffractive surface, it is possible to reduce the thickness of the optical element on which the diffractive surface is formed or another optical element constituting the scanning optical unit.

A scanning optical device using this diffractive optical element has been proposed, for example, in Japanese Patent Laid-Open No. 8-234127. In this publication, the scanning optical means is composed of one or a plurality of optical elements, and one of a plurality of surfaces of the optical element is formed of a diffractive optical surface, so that the diffractive optical surface also has power. The light flux is focused on a predetermined surface by diffraction and refraction.

However, when the optical element constituting the scanning optical means is molded from a plastic material, there is a problem that the refractive index changes due to environmental fluctuation due to a temperature change of the apparatus, and the optical performance is greatly deteriorated. For example, when the refractive index of the plastic material changes, the focus position changes, which affects image formation. Further, there is a problem that the power due to diffraction fluctuates due to the wavelength fluctuation of the semiconductor laser as the light source due to the temperature change, and the focus position fluctuates.

In Japanese Patent Application Laid-Open No. 8-234127, an optical element having a diffractive optical surface is disposed at a substantially intermediate position between the optical deflector and the surface to be scanned or on the surface to be scanned. The outer shape becomes very large. Also, when the optical element has power due to diffraction in the main scanning direction, the pitch gradually decreases from the center to the peripheral part of the optical element. However, there is a problem that it is disadvantageous, and furthermore, the diffraction efficiency is reduced.

A first object of the present invention is to provide a scanning optical means with a first optical element having no power due to refraction and an anamorphic lens having different convex refractive power due to refraction in both the main scanning direction and the sub-scanning direction. By forming a diffraction grating (diffractive optical element) having a convex power due to diffraction on at least one surface of the first optical element, the second optical element is constituted by two pieces of a certain second optical element. Another object of the present invention is to provide a scanning optical device having a simple configuration.

A second object of the present invention is to provide a first optical element which is a cylindrical lens having a convex power due to refraction in the sub-scanning direction, and a different convex refractive power due to refraction in both the main scanning direction and the sub-scanning direction. By forming a diffraction grating (diffractive optical element) having a convex power due to diffraction on at least one surface of the first optical element, the second optical element being an anamorphic lens having Another object of the present invention is to provide a scanning optical device having a high definition and a simple configuration.

[0010]

According to the present invention, there is provided a scanning optical apparatus comprising: (1) a light beam emitted from a light source device is deflected by a deflecting device, and the light beam deflected by the deflecting device is scanned by a scanning optical device onto a surface to be scanned; In a scanning optical device for guiding light upward and optically scanning the surface to be scanned, the scanning optical means includes a first optical element having no power due to refraction, and a refraction in both the main scanning direction and the sub-scanning direction. And a second optical element composed of an anamorphic lens having a different positive power according to the first optical element, and a diffraction grating having a positive power due to diffraction is formed on at least one surface of the first optical element.

In particular, (1-1) the first optical element has a flat transparent plate on both surfaces, and (1-2) both surfaces of the first optical element have the same radius of curvature. (1-3) the diffraction grating has different positive power due to diffraction in both the main scanning direction and the sub-scanning direction, and (1-4) the diffraction grating has a grating structure formed in a sawtooth shape. What you are doing,
(1-5) that the diffraction grating has a grating structure formed in a stepped manner, and (1-6) the diffraction grating has a grating pitch of P,
When the height from the base surface is H, it is formed so as to satisfy the condition of P / H> 3.
7) the shape of the periphery of both surfaces in the main scanning section of the second optical element on the optical axis is convex toward the deflecting means side, and (1-8) the first and second optical elements And (1-9) the scanning optical means is capable of changing the focus fluctuation in the main scanning direction and / or the sub-scanning direction caused by the environmental fluctuation of the apparatus, and the wavelength fluctuation of the light source means. And correction by the change of the diffraction power of the diffraction grating caused by the above.

(2) The light beam emitted from the light source means is deflected by the deflecting means, and the light beam deflected by the deflecting means is guided by the scanning optical means onto the surface to be scanned, and the light is irradiated on the surface to be scanned. In a scanning optical apparatus for scanning, the scanning optical means includes a first optical element composed of a cylindrical lens having a positive power due to refraction in a sub-scanning direction, and a different positive power due to refraction in both the main scanning direction and the sub-scanning direction. And a second optical element composed of an anamorphic lens having the following formula: wherein a diffraction grating having a positive power due to diffraction is formed on at least one surface of the first optical element.

In particular, (2-1) the diffraction grating has a different positive power due to diffraction in both the main scanning direction and the sub-scanning direction, and (2-2) the diffraction grating has a grating structure. That it is formed in a sawtooth shape, (2-3) that the diffraction grating has a grating structure formed in a stepped shape, and (2-4) that the diffraction grating has a grating pitch of P, from the base surface. When the height of H is H, P / H> 3 is satisfied, and (2-
5) The shape on the optical axis of both surfaces in the main scanning cross section of the second optical element has a convex shape facing the deflecting means side, and (2-6) the first and second optical elements are And (2-7) the scanning optical means converts the focus fluctuation in the main scanning direction and / or the sub-scanning direction caused by the environmental fluctuation of the apparatus into the wavelength fluctuation of the light source means. The correction is made by the change in the diffraction power of the diffraction grating caused by the change.

[0014]

(Embodiment 1) FIG. 1 is a sectional view (main scanning sectional view) of a main portion of a scanning optical device according to Embodiment 1 of the present invention in the main scanning direction.

In FIG. 1, reference numeral 1 denotes a light source means, which is composed of, for example, a semiconductor laser. A collimator lens 2 converts a divergent light beam emitted from the light source 1 into a substantially parallel light beam. Reference numeral 3 denotes an aperture stop, which shapes a light beam emitted from the collimator lens 2 into a desired optimum beam shape. Reference numeral 4 denotes a cylindrical lens which has a predetermined power (refractive power) in the sub-scanning direction and forms an image of a light beam emitted from the aperture stop 3 on a deflecting surface 5a of a deflecting means 5 to be described later in a sub-scanning section (see FIG. In the main scanning section, a long line image is formed. Reference numeral 5 denotes an optical deflector as a deflecting means, which is, for example, a rotating polygon mirror, and is rotated at a constant speed in a direction indicated by an arrow A in the figure by a driving means (not shown) such as a motor.

Numeral 6 denotes scanning optical means having fθ characteristics. First and second optical elements (fθ lens system) 6a, 6b
have. The first optical element 6a composed of a diffraction system having no power due to refraction is formed of a transparent flat plate having both surfaces flat in both the main scanning direction and the sub-scanning direction. Different positive (convex) for both
A diffraction grating (diffractive optical element) 8 is formed on the second surface (light emitting surface) 6a2 such that The diffraction grating 8
The grating structure is composed of, for example, a binary diffraction grating having a step shape or a Fresnel diffraction grating having a sawtooth shape.

The second optical element 6b made of a refracting system is made up of an anamorphic lens having a positive (convex) power that is different in both the main scanning direction and the sub-scanning direction, and has a first surface (light incident surface) 6b1 and a second surface. (Light Emitting Surface) 6b2 is formed of a toric surface. The main scanning direction is the first surface 6b1,
The second surface 6b2 has an aspherical shape, and the sub-scanning direction changes continuously as the radius of curvature of the second surface 6b2 increases as the distance from the optical axis increases. The shape of the periphery of the second optical element 6b on the optical axis on both surfaces in the main scanning section is convex toward the optical deflector. The first and second optical elements 6a and 6b are both formed of a plastic material. Scanning optical means 6
Has a tilt correction function by making the deflecting surface 5a and the scanned surface 7 conjugate in the sub-scanning cross section. 7 is a photosensitive drum surface (recording medium surface) as a surface to be scanned
It is.

In this embodiment, a divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by a collimator lens 2, shaped into a desired beam shape by an aperture stop 3, and is incident on a cylindrical lens 4. The light beam incident on the cylindrical lens 4 is emitted as it is in the main scanning section. Further, within the sub-scan section, the light converges and forms an almost linear image (a linear image elongated in the main scanning direction) on the deflecting surface 5a of the optical deflector 5. The light beam reflected and deflected by the deflecting surface 5a of the optical deflector 5 is formed into a spot image on the photosensitive drum surface 7 by the scanning optical means 6, and the optical deflector 5 is rotated in the direction of arrow A, thereby Optical scanning is performed on the photosensitive drum surface 7 at a constant speed in the direction of arrow B (main scanning direction). Thus, an image is recorded on the photosensitive drum surface 7 as a recording medium.

The first optical element 6a and the second optical element 6b constituting the scanning optical means 6 according to the present embodiment have a refractive system and a diffractive system each having an origin at an intersection between each optical element surface and the optical axis. If the direction of the optical axis is the X axis, the direction perpendicular to the optical axis in the main scanning section is the Y axis, and the direction perpendicular to the optical axis in the sub-scanning section is the Z axis, they can be expressed as follows.

Refractive system Main scanning direction: Aspherical shape expressed by the following function up to 10th order

[0021]

(Equation 1) Where R is the radius of curvature, k, B ₄ , B ₆ , B ₈ , and B ₁₀ are aspherical coefficients (when the coefficient has a suffix u, the laser is closer to the laser than the optical axis. side) sub-scanning direction ... curvature radius changes continuously in the Y-axis direction spherical r '= r (1 + D 2 Y 2 + D 4 Y 4 + D 6 Y 6 + D 8 Y
⁸ + D ₁₀ Y ¹⁰ ) where r is the radius of curvature, D ₂ , D ₄ , D ₆ , D ₈ , and D ₁₀ are aspherical coefficients (when the coefficient has a suffix u, the coefficient on the laser side from the optical axis has a suffix 1) In the case, the anti-laser side from the optical axis) Diffraction surface Diffraction surface represented by a phase function of a width polynomial up to the tenth order of Y and Z W = C ₁ Y + C ₂ Y ² + C ₃ Y ³ + C ₄ Y ⁴ + C ₅ Y ^{5
_{+ C 6 Y 6 + C 7}} Y 7 + C 8 Y 8 + C 9 Y 9 + C 10 Y 10
^{_{+ E 1 Z 2 + E 2}} YZ 2 + E 3 Y 2 Z 2 + E 4 Y 3 Z 2
^{_{+ E 5 Y 4 Z 2 +}} E 6 Y 5 Z 2 + E 7 Y 6 Z 2 + E 8 Y 7
Z ² + E ₉ Y ⁸ Z ² (C _{1 to} C ₁₀ and E _{1 to} E ₉ are phase coefficients) Here, when the grating pitch of the diffraction grating 8 is P and the height from the base surface is H, P / H > 3... (1) The shape of the diffraction grating 8 is formed so as to satisfy the following condition. Conditional expression (1) relates to the ratio between the grating pitch P of the diffraction grating 8 and the height H from the base surface. If conditional expression (1) is not satisfied, the diffraction efficiency is deteriorated, and good image plane illuminance cannot be obtained. On the other hand, when the lattice pitch P is small, the molding stability, the mold processing and the like are affected, which is not good.

Table 1 shows the optical arrangement in this embodiment, and Table 2 shows the aspherical coefficients of the refraction system and the phase coefficients of the diffraction system. FIG. 2 is an explanatory diagram showing the power in the main scanning direction in the diffraction system of the first optical element, and FIG. 3 is an explanatory diagram showing the ratio (aspect ratio) of the conditional expression (1) in the main scanning direction.

[0023]

[Table 1]

[0024]

[Table 2] In this embodiment, the minimum value of the ratio (aspect ratio) between the grating pitch P of the diffraction grating 6 and the height H from the base surface is P / H = 18.22 (24 mm in the main scanning direction from the optical axis).
Which satisfies the conditional expression (1).

Further, the scanning optical means 6 in the present embodiment.
Is to correct the focus fluctuation in the main scanning direction and / or the sub-scanning direction caused by the environmental fluctuation (particularly the temperature fluctuation) of the apparatus by the change of the diffraction power of the diffraction grating 8 caused by the wavelength fluctuation of the light source means (semiconductor laser) 1. are doing.

FIG. 4 is a diagram showing the field curvature in the main scanning direction before and after the temperature rise in this embodiment, and FIG. 5 is a diagram showing the field curvature in the sub-scanning direction before and after the temperature rise in this embodiment. 6 is a diagram showing distortion (fθ characteristic), image height deviation, and the like in the present embodiment. In the field curvature shown in FIGS. 4 and 5, the dotted line indicates the field curvature at a normal temperature of 25 ° C., and the solid line indicates the field curvature at a temperature rise of 25 ° C. and 50 ° C. Where 25
The refractive index n ^* of the first optical element 6a and the second optical element 6b and the wavelength λ ^* of the light source means 1 when the temperature is raised by ° C. are n ^* = 1.5212 λ ^* = 786.4 nm, respectively. is there. It can be seen from the figure that the focus movement is well corrected in both the main scanning direction and the sub-scanning direction.

Further, in the present embodiment, both the first and second optical elements 6a and 6b of the scanning optical means are arranged such that the central axes of the first and second optical elements 6a and 6b are perpendicular to the optical axis with respect to the optical axis. It is shifted by 3 mm. Thereby, the optical performance is favorably corrected.

As described above, in this embodiment, the first and second optical elements 6a and 6b constituting the scanning optical means 6 as described above.
By forming the diffraction grating 8 on the second surface 6b2 of the first optical element 6a, it is possible to obtain high-definition printing with a simple configuration that is resistant to focus changes due to environmental changes (particularly temperature changes). Obtain a small scanning optical device.

(Embodiment 2) FIG. 7 shows Embodiment 2 of the present invention.
FIG. 3 is a cross-sectional view (main scanning cross-sectional view) of a main part of the scanning optical device in the main scanning direction. In the figure, the same elements as those shown in FIG. 1 are denoted by the same reference numerals.

The difference between the first embodiment and the first embodiment is that both surfaces of the first optical element made of a diffractive system have the same radius of curvature in the main scanning direction, and both have infinite radii of curvature in the sub-scanning direction. (∞). Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

That is, in the figure, reference numeral 26 denotes scanning optical means having fθ characteristics, and has first and second optical elements (fθ lens system) 26a and 26b. Both surfaces of the first optical element 26a composed of a diffraction system having no power due to refraction have the same radius of curvature in the main scanning direction, and both have infinity (∞) in the sub-scanning direction. That is, the first optical element in the first embodiment is bent in the main scanning direction. Here, the second surface (light emitting surface) 26 is so set that the power by the diffraction system is different (positive) in both the main scanning direction and the sub-scanning direction.
A diffraction grating (diffractive optical element) 28 is formed on a2.

The second optical element 26b made of a refracting system is made of an anamorphic lens having a positive (convex) power that is different in both the main scanning direction and the sub-scanning direction, and the first surface 26b.
Both the first and second surfaces 26b2 are formed of toric surfaces. In the main scanning direction, both the first surface 26b1 and the second surface 26b2 have an aspheric shape, and in the sub-scanning direction, the first surface 26b1,
The radius of curvature of the second surface 26b2 continuously changes as the distance from the optical axis increases. The shape of the periphery of the second optical element 26b on the optical axis on both surfaces in the main scanning section is convex toward the optical deflector. First and second optical elements 26a, 26
6b is formed of a plastic material. Further, the scanning optical means 26 has a tilt correction function by making the deflecting surface 5a and the scanned surface 7 conjugate in the sub-scanning section.

Table 3 shows the optical arrangement in the present embodiment, and Table 4 shows the aspherical coefficient of the refraction system and the phase coefficient of the diffraction system. FIG. 8 is an explanatory diagram showing the power in the main scanning direction in the diffraction system of the first optical element, and FIG. 9 is an explanatory diagram showing the ratio (aspect ratio) of the conditional expression (1) in the main scanning direction.

[0034]

[Table 3]

[0035]

[Table 4] In this embodiment, the minimum value of the ratio (aspect ratio) between the grating pitch P of the diffraction grating and the height H from the base surface is P / H = 3.69 (a position 24 mm from the optical axis in the main scanning direction). This satisfies conditional expression (1).

Further, the scanning optical means 2 in the present embodiment
Numeral 6 corrects a focus variation in the main scanning direction and / or the sub-scanning direction caused by an environmental change (particularly a temperature change) in the apparatus by a change in the diffraction power of the diffraction grating 28 caused by a wavelength change of the light source means 1. I have.

FIG. 10 is a diagram showing the curvature of field in the main scanning direction before and after the temperature rise in this embodiment, and FIG. 11 is a diagram showing the curvature of field in the sub-scanning direction before and after the temperature rise in this embodiment. 12 is a diagram showing distortion (fθ characteristic), image height deviation, and the like in the present embodiment. In the field curvature shown in FIGS. 10 and 11, the dotted line indicates the field curvature at a normal temperature of 25 ° C., and the solid line indicates the field curvature at a temperature rise of 25 ° C. and 50 ° C.
Here, when the temperature is raised by 25 ° C., the refractive index n ^* of the first optical element 26a and the second optical element 26b and the wavelength λ ^* of the light source means 1 are n ^* = 1.5212 λ ^* = 786. 4 nm. It can be seen from the figure that the focus movement is well corrected in both the main scanning direction and the sub-scanning direction.

Further, in the present embodiment, both the first and second optical elements 26a and 26b of the scanning optical means 26 have their central axes within the deflection plane in the direction perpendicular to the optical axis and away from the light source means 1. .3 mm. Thereby, the optical performance is favorably corrected.

As described above, in this embodiment, the first and second optical elements 26a, 26a,
By forming the diffraction grating 28 on the second surface 26a2 of the first optical element 26 of the first optical element 26b, a simple configuration that is resistant to focus changes due to environmental changes (particularly temperature changes) can be obtained.
A small scanning optical device capable of obtaining high-definition printing has been obtained.

(Embodiment 3) FIG. 13 is a sectional view (main scanning sectional view) of a main portion of a third embodiment of the present invention in the main scanning direction.
In the figure, the same elements as those shown in FIG. 1 are denoted by the same reference numerals.

This embodiment is different from the first embodiment in that the first optical element is formed of a cylindrical surface having a positive (convex) power in the sub-scanning direction.
That is, the second surface is formed of a planar cylindrical lens, and a diffraction grating is formed on the second surface. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

That is, in the figure, reference numeral 36 denotes scanning optical means having fθ characteristics, and has first and second optical elements (fθ lens system) 36a and 36b. The first optical element 36a is a cylindrical lens having a first surface 36a1 having a cylindrical surface having a power that is convex in the sub-scanning direction, and a second surface 36a2 having a flat surface. The diffraction grating (diffractive optical element) 3 is provided on the second surface 36a2 so that the power of the diffraction system becomes positive (convex) in both the main scanning direction and the sub-scanning direction.
8 are formed. That is, the first optical element 36a has both the power by the refraction system and the power by the diffraction system in the sub-scanning direction.

The second optical element 36b made of a refracting system is made of an anamorphic lens having different positive (convex) powers in both the main scanning direction and the sub-scanning direction.
Both the first and second surfaces 36b2 are formed of toric surfaces. In the main scanning direction, both the first surface 36b1 and the second surface 36b2 have an aspheric shape, and in the sub-scanning direction, the radius of curvature of the second surface 36b2 changes continuously as the distance from the optical axis increases. The shape of the periphery of both surfaces of the second optical element 36b in the main scanning section on the optical axis is convex toward the optical deflector. The first and second optical elements 36a and 36b are both formed of a plastic material. Further, the scanning optical means 36
Has a tilt correction function by making the deflecting surface 5a and the scanned surface 7 conjugate in the sub-scanning cross section.

Table 5 shows the optical arrangement in this embodiment, and Table 6 shows the aspherical coefficient of the refraction system and the phase coefficient of the diffraction system. FIG. 14 is an explanatory diagram showing the power in the main scanning direction in the diffraction system of the first optical element, and FIG. 15 is an explanatory diagram showing the ratio (aspect ratio) of the conditional expression (1) in the main scanning direction.

[0045]

[Table 5]

[0046]

[Table 6] In the present embodiment, the minimum value of the ratio (aspect ratio) between the grating pitch P of the diffraction grating 38 and the height H from the base surface is P / H = 5.61 (a position 24 mm from the optical axis in the main scanning direction). This satisfies the conditional expression (1).

Further, the scanning optical means 3 in the present embodiment
Numeral 6 corrects a focus variation in the main scanning direction and / or the sub-scanning direction caused by an environmental change (particularly a temperature change) of the apparatus by a change in diffraction power of the diffraction grating 38 caused by a wavelength change of the light source 1. I have.

FIG. 16 is a diagram showing the field curvature in the main scanning direction before and after the temperature rise in this embodiment, and FIG. 17 is a diagram showing the field curvature in the sub-scanning direction before and after the temperature rise in this embodiment. 18 is a diagram illustrating distortion (fθ characteristic), image height deviation, and the like in the present embodiment. In the field curvature shown in FIGS. 16 and 17, the dotted line indicates the field curvature at a normal temperature of 25 ° C., and the solid line indicates the field curvature at a temperature of 25 ° C. and 50 ° C.
Wherein the refractive index of the first optical element 36a and the second optical element 36b when the 25 ° C. temperature rise n ^*, and each wavelength lambda ^* is the light source means ^{1, n * = 1.5212 λ *} = 786. 4 nm. It can be seen from the figure that the focus movement is well corrected in both the main scanning direction and the sub-scanning direction.

Further, in the present embodiment, both the first and second optical elements 36a and 36b of the scanning optical means 36 have their central axes within the deflecting plane in a direction perpendicular to the optical axis and away from the light source means 1. .3 mm. Thereby, the optical performance is favorably corrected.

As described above, in the present embodiment, the first and second optical elements 36a, 36a,
By forming the diffraction grating 38 on the second surface 36a2 of the first optical element 36a of the first optical element 36b, it is possible to obtain high-definition printing with a simple configuration that is resistant to focus changes due to environmental changes (particularly temperature changes). To obtain a small scanning optical device.

In each of the embodiments, the light beam emitted from the light source is converted into substantially parallel light by the collimator lens. However, the light beam is converted into a focused light beam in order to reduce the distance between the deflecting surface and the surface to be scanned. You may.

In each embodiment, the first and second optical elements are provided within the deflection plane to correct the inclination of the curvature of field.
Although the center axis is shifted in a direction perpendicular to the optical axis, the first and second optical elements are placed in a deflection plane to correct the field curvature and the fθ characteristic. It may be inclined with respect to the axis.

[0053]

According to the first invention, as described above, the first optical element having no power due to refraction of the scanning optical means,
The second optical element is an anamorphic lens having different convex refractive powers due to refraction in both the main scanning direction and the sub-scanning direction. At least one surface of the first optical element has a convex power due to diffraction. By forming the diffraction grating (diffractive optical element) having the above, it is possible to achieve a high-definition, compact, and simple scanning optical device.

According to the second aspect of the present invention, as described above, the first optical element which is a cylindrical lens having a convex power due to refraction in the sub-scanning direction, and a different convex due to refraction in both the main scanning direction and the sub-scanning direction. The second optical element, which is an anamorphic lens having a refractive power of
By forming a diffraction grating (diffractive optical element) having a convex power due to diffraction on at least one surface of the optical element described above, it is possible to achieve a scanning optical apparatus having a high definition and a simple configuration.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part in a main scanning direction according to a first embodiment of the present invention (a main scanning sectional view);

FIG. 2 is an explanatory diagram showing power in a main scanning direction in a diffraction system of the first optical element according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an aspect ratio of a diffraction grating shape of the first optical element according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a field curvature in a main scanning direction before and after a temperature rise according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a field curvature in a sub-scanning direction before and after a temperature rise according to the first embodiment of the present invention.

FIG. 6 shows distortion (fθ characteristic) according to the first embodiment of the present invention.
Diagram showing image height deviation

FIG. 7 is a cross-sectional view of main parts in the main scanning direction according to the second embodiment of the present invention (main-scanning cross-sectional view).

FIG. 8 is an explanatory diagram showing the power in the main scanning direction in the diffraction system of the first optical element according to the second embodiment of the present invention.

FIG. 9 is an explanatory diagram showing an aspect ratio of a diffraction grating shape of the first optical element according to the second embodiment of the present invention.

FIG. 10 is a diagram illustrating a field curvature in a main scanning direction before and after a temperature rise according to a second embodiment of the present invention.

FIG. 11 is a diagram illustrating a field curvature in a sub-scanning direction before and after a temperature rise according to a second embodiment of the present invention.

FIG. 12 is a diagram illustrating distortion (fθ characteristic) and image height deviation according to the second embodiment of the present invention.

FIG. 13 is a cross-sectional view of main parts in the main scanning direction (main scanning cross-sectional view) according to the third embodiment of the present invention.

FIG. 14 is an explanatory diagram showing the power in the main scanning direction in the diffraction system of the first optical element according to the third embodiment of the present invention.

FIG. 15 is an explanatory diagram showing an aspect ratio of a diffraction grating shape of the first optical element according to the third embodiment of the present invention.

FIG. 16 is a diagram illustrating a field curvature in a main scanning direction before and after a temperature rise according to a third embodiment of the present invention.

FIG. 17 is a diagram illustrating a field curvature in a sub-scanning direction before and after a temperature rise according to a third embodiment of the present invention.

FIG. 18 is a diagram illustrating distortion (fθ characteristic) and image height deviation according to the third embodiment of the present invention.

FIG. 19 is a cross-sectional view of a main part of a conventional scanning optical device in a main scanning direction (main scanning cross-sectional view).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source means (semiconductor laser) 2 Collimator lens 3 Aperture stop 4 Cylindrical lens 5 Deflection means (rotating polygon mirror) 5a Deflection surface 6,26,36 Scanning optical hand-throw 6a, 26a, 36a First optical element 6b, 26b, 36b Second optical element 8, 28, 38 Diffraction grating (diffractive optical element) 7 Scanned surface (photosensitive drum surface)

Claims (18)

[Claims] 1. A light beam emitted from a light source means is deflected by a deflecting means, and a light beam deflected by the deflecting means is guided by a scanning optical means onto a surface to be scanned, thereby optically scanning the surface to be scanned. A scanning optical device, wherein the scanning optical means comprises a first optical element having no power due to refraction, and a second optical element comprising an anamorphic lens having different positive power due to refraction in both the main scanning direction and the sub-scanning direction. And a diffraction grating having a positive power due to diffraction is formed on at least one surface of the first optical element. 2. The scanning optical device according to claim 1, wherein said first optical element is formed of a transparent flat plate having two flat surfaces. 3. The scanning optical device according to claim 1, wherein both surfaces of said first optical element have the same radius of curvature. 4. The scanning optical device according to claim 1, wherein the diffraction grating has different positive powers due to diffraction in both the main scanning direction and the sub-scanning direction. 5. The scanning optical device according to claim 1, wherein the diffraction grating has a grating structure formed in a sawtooth shape. 6. The scanning optical device according to claim 1, wherein the diffraction grating has a grating structure formed in a stepped shape. 7. The diffraction grating is formed so as to satisfy a condition of P / H> 3, where P is a grating pitch and H is a height from a base surface. 7. The scanning optical device according to 4, 5, or 6. 8. The scanning optical apparatus according to claim 1, wherein the shape of the periphery of both surfaces in the main scanning section of the second optical element on the optical axis is convex toward the deflecting means. 9. The method according to claim 1, wherein the first and second optical elements are both formed of a plastic material.
4. The scanning optical device according to 2 or 3. 10. The scanning optical means changes the focus fluctuation in the main scanning direction and / or the sub-scanning direction caused by the environmental fluctuation of the apparatus by changing the diffraction power of the diffraction grating caused by the wavelength fluctuation of the light source means. 2. The scanning optical device according to claim 1, wherein the correction is performed. 11. A light beam emitted from a light source means is deflected by a deflecting means, and a light beam deflected by the deflecting means is guided to a surface to be scanned by a scanning optical means, thereby optically scanning the surface to be scanned. In the scanning optical device, the scanning optical unit includes a first optical element composed of a cylindrical lens having a positive power due to refraction in the sub-scanning direction, and a different positive power due to refraction in both the main scanning direction and the sub-scanning direction. Having an anamorphic lens having a second
And at least one of the first optical elements
A scanning optical device, wherein a diffraction grating having a positive power due to diffraction is formed on a surface. 12. The scanning optical device according to claim 11, wherein the diffraction grating has different positive powers due to diffraction in both the main scanning direction and the sub-scanning direction. 13. The diffraction grating according to claim 11, wherein the grating structure is formed in a saw-tooth shape.
The scanning optical device according to claim 1. 14. The diffraction grating according to claim 11, wherein the diffraction grating has a grating structure formed in a stepped shape.
The scanning optical device according to claim 1. 15. The diffraction grating according to claim 11, wherein, when the grating pitch is P and the height from the base surface is H, the condition P / H> 3 is satisfied. 15. The scanning optical device according to claim 12, 13, 13, or 14. 16. The scanning optical apparatus according to claim 11, wherein the shape of the second optical element on the optical axis on both surfaces in the main scanning section is convex toward the deflecting means. 17. The apparatus according to claim 1, wherein the first and second optical elements are both formed of a plastic material.
2. The scanning optical device according to 1. 18. The scanning optical unit according to claim 1, wherein a focus variation in a main scanning direction and / or a sub-scanning direction caused by an environmental variation of the apparatus is caused by a change in diffraction power of the diffraction grating caused by a wavelength variation of the light source unit. The scanning optical device according to claim 11, wherein the correction is performed.