JPH0727991A - Optical scanner - Google Patents

Abstract

PURPOSE:To improve the optical characteristic of an optical scanner in which the reflection area of a scanning mirror on which the outgoing light of a laser beam source is made skew-incident is formed with a curved surface having a negative power in a main scanning direction and a plane to be scanned is arranged on the main scanning optical path of the scanning mirror via a correction lens. CONSTITUTION:The light incident plane 57 of the correction lens 45 is formed with a rotation symmetric curved surface in which an envelope is made a high- degree curve of even-numbered degree while displacing a rotary axis parallel with the main scanning direction from the center of the main scanning optical path to a sub-scanning direction, and the light emitting plane 59 of the correction lens 45 is formed with the rotation symmetric curved surface in which the envelope is made the high-degree curve of even-numbered degree while locating the rotary axis crossing orthogonally the main scanning direction and a sub-scanning direction in the center of the main scanning optical path, thereby, various kinds of optical aberration can be reduced, and also, the emitting direction of stray light is kept away from the main scanning optical path.

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 using a laser beam used in a laser printer, a laser facsimile, a digital copying machine and the like.

[0002]

2. Description of the Related Art In recent years, an electrophotographic method has been developed as a simple and high-quality printing method, and an optical scanning device is known as a method for realizing it. With this optical scanning device, a polygon mirror having a large number of reflecting surfaces connected to the outer periphery is attached to the rotating shaft of a driving device and arranged on the emission optical path of a laser light source, and on the reflection optical path of the reflecting surface of the polygon mirror. The photosensitive member is positioned so that the photosensitive surface moves relatively in the sub scanning direction.

The applicant of the present invention has disclosed in Japanese Patent Laid-Open Nos. 1-177011 and 1-177512 that the light incident surface of a cylindrical lens for correcting plane tilt is the same as the rotary axis parallel to the main scanning direction. Is formed by a non-cylindrical rotationally symmetric curved surface having a plane of symmetry perpendicular to the polygon mirror and including the axis of rotation of the polygon mirror, and the light emitting surface of this cylindrical lens has a plane of symmetry that is the same as the axis of rotation of the light incident surface. It has also been proposed to form a curved surface having a high power and to combine it with the polygon mirror having the above structure to better correct the field curvature and the fθ error.

Therefore, here, the optical scanning device disclosed in Japanese Patent Laid-Open No. 1-177011 will be described as a prior art with reference to FIGS. First, in the optical scanning device 3, as illustrated in FIG. 7, the semiconductor laser oscillator 7 which is a laser light source in which the collimator lens 4 and the imaging lens 5 are sequentially arranged on the optical axis 6 causes the drive motor 8 to rotate. A polygon mirror 10, which is a scanning mirror rotatably supported by a shaft 9, faces a reflecting surface 11 having negative power from diagonally below. Then, on the reflection optical path formed obliquely upward from the reflection surface 11,
The surface to be scanned of the photosensitive drum 13 which is rotatable via the correction lens 12 is arranged, and the optical scanning device 3 has a rotating reflecting surface 1
A skew optical system in which the optical axes 6 of the incident light and the emitted light are inclined with respect to 1 is formed.

As shown in FIG. 8, the polygon mirror 10 has a reflecting surface 11 formed as an elliptic cylindrical surface having an elliptical cross section with radii a and b on an inscribed circle with a radius c. It has a shape that is serially connected to six. Then, the image forming lens 5 and the like reflect the incident light beam into the polygon mirror 1.
It converges on a virtual convergence point S behind the reflection surface 11 of 0.

Further, in the optical scanning device 3, the light incident surface of the correction lens 12 facing the polygon mirror 10 has a rotary shaft 14 parallel to the main scanning direction, which is the photosensitive drum 1.
It is formed by a rotationally symmetric curved surface located between the scanning surface 3 and
The light emitting surface of the correction lens 12 facing the surface to be scanned of the photosensitive drum 13 is formed by a rotationally symmetrical curved surface in which a rotation axis 15 orthogonal to the main scanning direction and the sub scanning direction is located in the center of the main scanning region. ing.

More specifically, as illustrated in FIG. 9, a reference axis X ₁ parallel to the main scanning direction is set on the center point O ₁ of the light incident surface 16 of the correction lens 12, and the main scanning direction and the sub-scanning direction are set. When the reference axis Y ₁ that is orthogonal to the scanning direction is set, the envelope of a cross-sectional shape that is orthogonal to the sub-scanning direction of the light incident surface 16 is formed on the Y ₁ O ₁ X ₁ coordinate of an eight-dimensional higher-order curve. polynomial has a ^{_{Y 1 = α 2 X 1 2}} + α 4 X 1 4 + α 6 X 1 6 + α 8 X 1 8 -e 1. Similarly, the light exit surface 17 of the correction lens 12
If a reference axis Y ₂ orthogonal to the main scanning direction and the sub-scanning direction is set on the center point O _{2 of the} and the reference axis X ₂ parallel to the main scanning direction is set at a position of the distance e ₂ , 17
The polynomial of the 8th-order higher-order curve forming the envelope of the cross-sectional shape orthogonal to the sub-scanning direction is: Y ₂ = β ₂ X ₂ ² + β ₄ X ₂ ⁴ + β ₆ X ₂ ⁶ + β ₈ X ₂ ⁸ −e _{It is 2} .

By doing so, the optical scanning device 3
Then, the light incident surface of the correction lens 12 has a positive power in the sub-scanning direction and a negative power in the main scanning direction, and the light exit surface of the correction lens 12 has a negative power in the main scanning direction in the central portion. It has power, and positive power in the periphery. The power referred to here means the refracting power of the optical surface and the imaging power.

In such a configuration, when the optical characteristics of the optical scanning device 3 were set and the optical characteristics were examined by simulation, it was confirmed that optical aberrations such as fθ error and field curvature could be corrected well.

[0010]

By forming the correction lens 12 and the like in the shape as described above, it is possible to obtain the optical scanning device 3 and the like having good optical characteristics.

However, when the present applicant examined the optical characteristics of the optical scanning device 3 as described above in detail, the correction lens 1
Since the coma aberration is generated in the beam light due to the influence of the two light incident surfaces 16, the conventional method of evaluating each field curvature by the displacement of both ends of the beam light in each scanning direction matches the actual spot light shape. It turned out not to. That is, the two main scanning peripheral beams are curved in the main scanning direction and the sub-scanning direction due to the coma aberration of the light incident surface 16 of the correction lens 12,
In particular, it was found that the spot light was deformed and the area was increased outside the main scanning region.

Further, in the simulation of the optical scanning device 3 as described above, generally only the optical characteristics of the beam light transmitted through the correction lens 12 are evaluated, but in reality, the light incident surface 16 of the correction lens 12 is evaluated. The light emitting surface 17 reflects a part of the beam light incident from the light emitting surface 17, the light incident surface 16 reflects the light, and the light emitting surface 17 transmits the light. Of the stray light emitted from the light exit surface 17 by the two internal reflections, the stray light in the peripheral portion of the correction lens 12 stays at a position slightly less than 90 (mm) from the center and is mainly Since it overlaps with the scanning line, the latent image carrier of the photosensitive drum 13 may be adversely affected.

Therefore, in the simulation of the optical scanning device 3 performed by the present applicant in consideration of the above problems, the parameters are first illustrated in Table 1, and then various parameters calculated in accordance with such parameters. Figure 1 shows the optical characteristics
A description will be given based on 0. The unit of the numerical value in the table is
The length is (mm) and the angle is (°).

[0014]

[Table 1]

When the optical characteristics are calculated by setting the above parameters in the optical scanning device 3, FIG.
Although the main-scanning field curvature illustrated in (b) is sufficiently small, the sub-scanning field curvature illustrated in (c) and the scanning line curvature illustrated in (d) are extremely large. It was found that the image quality deteriorates due to poor characteristics. Since the maximum value of the sub-scanning field curvature of FIG. 7C is 18.38 (mm), which is too large, this deviates from the display range of FIG. Further, the fθ error illustrated in FIG. 7A is too large, but this is not an important issue because it can be easily corrected at the operation timing of the semiconductor laser oscillator 7.

Further, regarding the optical scanning device 3 as described above, the optical characteristics of the stray light emitted from the light emitting surface 17 due to the two internal reflections of the correction lens 12 were investigated as described above. It was found that the displacement in the sub-scanning direction due to being deflected in the main scanning direction is very small like the light.
That is, in the optical scanning device 3, the stray light as described above is emitted to substantially the same position as the original scanning light, so that the photosensitive drum 13 is exposed.
This is extremely difficult to take and the image quality is degraded.

The present invention provides an optical scanning device having good optical characteristics.

[0018]

A scanning mirror having a reflecting surface on which light emitted from a laser light source is skew-incident is rotatably supported, and the reflecting surface of the scanning mirror is a curved surface having a negative power in a main scanning direction. The scanning mirror is formed by, a correction lens and a surface to be scanned are sequentially arranged on the main scanning optical path of the scanning mirror, and the surface to be scanned is positioned so as to be relatively movable in the sub-scanning direction with respect to the main scanning optical path.
The light-incident surface of the correction lens is formed by a rotationally symmetric curved surface whose rotation axis parallel to the main scanning direction is displaced from the center of the main scanning optical path in the sub-scanning direction and whose envelope becomes an even-order higher-order curve. The light emitting surface is formed by a rotationally symmetrical curved surface in which a rotation axis orthogonal to the main scanning direction and the sub-scanning direction is located at the center of the main scanning optical path and an envelope is an even-order higher-order curve.

[0019]

Since various optical aberrations can be reduced and the emission direction of stray light can be separated from the main scanning optical path, an optical scanning device having excellent optical characteristics can be obtained.

[0020]

Embodiments of the present invention will be described with reference to FIGS. First, in the post-objective type optical scanning device 18, as illustrated in FIGS. 1 to 3, a housing 21 is provided on a flat base 19 with three screws 20.
The light emitting unit 22 is attached to the upper part of the housing 21 while being inclined downward. The light emitting unit 22 includes a semiconductor laser oscillator 24, which is a laser light source mounted on a substrate 23, and a heat sink 2 made of metal.
The cylindrical collimator lens barrel 2 is fixed to the heat sink 25, slidably mounted on the heat sink 25, and then fixed by adhesion or the like.
6 has a structure in which a collimator lens 27 is fixed.

In the optical scanning device 18, a cylindrical lens 31, a plano-convex lens 32, and a reflection mirror 33 are provided below the inner frame 30 having two convex portions 28 and two screw holes 29 formed on the upper surface thereof. It is fixed by tilting, and the inner frame 30 is attached to the positions of the two recesses 34 on the upper and lower surfaces of the housing 21 with two screws 35, so that the cylindrical lens 31 is placed on the optical axis of the light emitting unit 22. The plano-convex lens 32 and the reflection mirror 33 are sequentially arranged.

Further, in the optical scanning device 18, a scanner motor 39 is formed by using the substrate 38 mounted on the base 19 with the four screws 37 via the spacer 36 as a part, and the scanner motor 39 is disposed vertically. A polygon mirror 41, which is a scanning mirror, is rotatably supported in the horizontal direction by a rotary shaft 40. The reflection optical paths of the reflection mirror 33 are incident on the four reflection surfaces 42 of the polygon mirror 41 from slightly above the horizontal.
This is a skew optical system in which the optical axes of the incident light and the emitted light are inclined with respect to the rotating reflecting surface 42. In this polygon mirror 41, each of the four reflecting surfaces 42 is an elliptic cylindrical surface having an elliptical cross-sectional shape, and the lenses 31, 32, etc. direct the incident light beam to the polygon mirror 41. It converges on a virtual convergence point behind the reflection surface 42.

Therefore, in the optical scanning device 18, the correction lens 45 is attached to the rectangular through hole 43 formed in the front surface of the housing 18 with the two screws 44 so as to be inclined downward, as illustrated in FIG. So that this correction lens 4
5 is arranged on the scanning optical path located obliquely below the reflecting surface 42 of the polygon mirror 41. Since the correction lens 45 of the optical scanning device 18 has a very special shape and is a characteristic part of the present invention, it will be described later in detail.

In the optical scanning device 18, as illustrated in FIGS. 1 to 3, elongated reflecting mirrors 48 are elastically slid at both ends in opening main recesses 47 formed on both sides of the outer frame 46 in the main scanning direction. While being mounted spontaneously, in a circular through hole 49 formed in the lower portion of the outer frame 46,
The reflecting mirror 50 elongated in the main scanning direction is provided with the cylindrical members 5 at both ends.
1 is rotatably mounted in the sub-scanning direction and then fixed by adhesion or the like. Here, the cylindrical member 51 is separately fixed to both ends of the reflection mirror 50, and an angle adjustment groove 52 for adjustment work with a flat head screwdriver (not shown) is formed on the outer surface thereof. . In addition, the external frame 46
A small reflecting mirror 53 is fixed to one side of the reflecting mirror 48, and a start sensor 54 is attached to the other side of the reflecting mirror 48 facing the reflecting mirror 53.

Therefore, in the optical scanning device 18, the external frame 46 is attached to the front surface of the housing 18 with the two screws 55, so that the reflected light positioned obliquely below the reflecting surface 42 of the polygon mirror 41. The reflection mirrors 48 and 53 are located on the road through the correction lens 45, the start sensor 54 is located on the reflection light path of the reflection mirror 53, and the reflection mirror 50 is located on the reflection light path of the reflection mirror 48. It is supposed to be located. Further, on the reflection optical path of the reflection mirror 50, the surface to be scanned of the photosensitive drum 56 that is rotatably supported in the sub scanning direction is positioned.

Further, in this optical scanning device 18, as illustrated in FIG. 4, the light incident surface 57 of the correction lens 45 is
A rotation axis 58 parallel to the main scanning direction is displaced from the center of the main scanning optical path in the sub-scanning direction to form a rotationally symmetric curved surface having an even-order higher-order curve, and the light exit surface 59 of the correction lens 45. Is a rotation axis 6 orthogonal to the main scanning direction and the sub scanning direction.
0 is located at the center of the main scanning optical path, and the envelope is formed by a rotationally symmetric curved surface that is an even-order higher-order curve.

More specifically, in the optical scanning device 18,
As illustrated in FIG. 5, the reference axis X ₁ parallel to the main scanning direction is set on the origin O ₁ displaced from the center point of the light incident surface 57 of the correction lens 45 in the sub scanning direction by the displacement amount Δ. When a reference axis Y ₁ orthogonal to the main scanning direction and the sub-scanning direction is set, a cross-sectional shape of the light incident surface 57 orthogonal to the sub-scanning direction is formed on the Y ₁ O ₁ X ₁ coordinates in an 8th-order higher order. polynomial curve becomes ^{_{Y 1 = α 2 X 1 2}} + α 4 X 1 4 + α 6 X 1 6 + α 8 X 1 8 -e 1.

In the optical scanning device 18, the reference axis Y ₂ orthogonal to the main scanning direction and the sub scanning direction is set on the center point O ₂ of the light emitting surface 59 of the correction lens 45, and the distance e ₂ is set. When the reference axis X ₂ parallel to the main scanning direction is set at the position of, the polynomial of the eighth-order higher-order curve forming the cross-sectional shape of the light emitting surface 59 orthogonal to the sub-scanning direction is Y ₂ = β ₂ X ₂ ² + β ₄ X ₂ ⁴ + β ₆ X ₂ ⁶ + β ₈ X ₂ ⁸ −e ₂ .

In the optical scanning device 18 having such a structure, the laser light emitted from the semiconductor laser oscillator 24 is collimated by the collimator lens 27 and then the lens 3 is formed.
The reflecting surface 42 of the polygon mirror 41 that converges and rotates by 1, 32 is deflected and scanned in the main scanning direction, and the main scanning light is optically corrected by the correction lens 45, and the rotating photosensitive drum 56 is moved in the sub scanning direction. Incident on the surface.

By doing so, the photosensitive drum 5
Since main scanning lines by optical scanning are sequentially formed on the surface to be scanned of 6 in the sub-scanning direction, for example, a charging device or a developing device is disposed on the surface to be scanned of the photosensitive drum 56 so as to be discharged by the charging device. An electrostatic latent image is formed on the surface to be scanned of the charged photosensitive drum 56 by optical scanning, and the electrostatic latent image is developed with toner supplied from a developing device and transferred to a recording medium, thereby forming an image by electrophotography. Forming can be performed. In the optical scanning device 18, the scanning light of the polygon mirror 41 is reflected by the reflection mirror 53 and received by the start sensor 54,
The above-mentioned image formation is performed according to the detection timing of the start sensor 54.

In the optical scanning device 18, the center of the shape of the light incident surface 57 of the correction lens 45 is displaced in the sub-scanning direction by the displacement amount Δ, so that the spot shape is deformed due to the coma aberration of the correction lens 45. The influence of stray light or the like due to internal reflection of the correction lens 45 is reduced, and the image quality is improved.

Therefore, the result of the simulation performed by the applicant of the present invention for evaluating the optical characteristics of the optical scanning device 18 will be described below by exemplifying the parameters in Table 2 below. The unit of numerical values in the table is (mm) for length and (°) for angle.

[0033]

[Table 2]

When various optical characteristics of the optical scanning device 18 were calculated by setting the above parameters and performing simulation, the main scanning field curvature illustrated in FIG. 6B and FIG. An example of the sub-scanning field curvature illustrated in FIG.
It was confirmed that the maximum value of the scanning line curve illustrated in FIG. 10 is sufficiently smaller than the optical characteristics of the conventional optical scanning device 3 illustrated in FIG. Although the fθ error illustrated in FIG. 7A is large as in the conventional optical scanning device 3 and the like, this is not an important issue because it can be easily corrected at the operation timing of the semiconductor laser oscillator 24.

Further, regarding the optical scanning device 18, the applicant of the present invention has a main scanning field curvature caused by a light component expanded in the sub-scanning direction of the beam light and a sub-scanning caused by a light component expanded in the main scanning direction of the beam light. When the scanning field curvature was also calculated by simulation, it was confirmed that these field curvatures were also extremely small, as illustrated by the broken lines in FIGS. 6B and 6C.

Further, regarding the optical scanning device 18, the applicant of the present invention has made the light emitting surface 59 by the internal reflection of the correction lens 45 twice.
When the optical characteristics of the stray light emitted from the device were investigated, it was confirmed that this was large in displacement in the sub-scanning direction as compared with the original scanning light. That is, in the optical scanning device 18, the stray light described above can be emitted to a position that is largely displaced in the sub-scanning direction with respect to the original scanning light.
It is extremely easy to take measures so that the light does not enter the light source 6, and it is possible to reduce noise components due to stray light and contribute to improving image quality.

A specific example of the method of adjusting the optical system of the optical scanning device 18 will be described below in detail together with the assembling process. First, the semiconductor laser oscillator 24 mounted on the substrate 23 is fixed to the metal heat sink 25, and the collimator lens 27
Is fixed to the collimator barrel 26, and the collimator barrel 2
A heat sink 25 is slidably attached to 6 to temporarily assemble the light emitting unit 22. Therefore, the collimator lens 27 of the light emitting unit 22 and the semiconductor laser oscillator 24
The centering adjustment is performed by an auto collimator (not shown), and the collimator lens barrel 26 and the heat sink 25 are fixed by adhesion or the like to complete the assembly of the light emitting unit 22.

Next, the light emitting unit 22 formed as described above is temporarily slidably assembled to the housing 21, and the inner frame 30 in which the lenses 31, 32 and the reflection mirror 33 are previously mounted is fixed to the housing 21 with the screw 35. Assemble. Then, in this state, the reflecting surface 4 of the polygon mirror 41
Place a two-dimensional area sensor (not shown) at position 2
One-dimensional adjustment of the light emitting unit 22 and position adjustment of the cylindrical lens 31 in the sub-scanning direction are roughly performed.

After the above-mentioned adjustment is completed, the two-dimensional area sensor is removed from the housing 21, and the housing 21 is fixed to the base 19 to which the polygon mirror 41 and the scanner motor 39 are assembled in advance with the screw 20. Then, the correction lens 45 is assembled with the screw 44. At this time, since the outer frame 46 is not attached to the front surface of the housing 21, a beam diameter evaluation device (not shown) is arranged at the focal position of the correction lens 45, and the beam diameter is evaluated by this beam diameter evaluation device. The one-dimensional adjustment of the light emitting unit 22 is performed with high accuracy.

Then, the light emitting unit 22 which has been subjected to the one-dimensional adjustment as described above is fixed to the housing 21,
The outer frame 46 in which the reflection mirrors 48 and 50 are mounted in advance is fixed to the housing 21 with screws 55. Therefore,
The optical scanning device 18 assembled as described above is assembled to the main body (not shown) of the laser printer, and the cylindrical portion 51 is rotated by a minus driver (not shown) to adjust the angle of the reflection mirror 50. After making it possible to irradiate the predetermined position of the photosensitive drum 56 with the scanning light, the cylindrical portion 51 is fixed to the outer frame 46 by adhesion or the like.

By doing so, the optical scanning device 1
In No. 8, since it is possible to obtain extremely good optical characteristics by a simple adjustment work, it is possible to contribute to the improvement of the productivity and print quality of the laser printer.

In the optical scanning device 18, the correction lens 45 having the above-mentioned optical characteristics is arranged at a position extremely close to the polygon mirror 41, so that the correction lens 45 can be obtained.
Since it can be shortened in the main scanning direction and the like, it is possible to contribute to reduction in size and weight of the entire apparatus.

Further, in the optical scanning device 18 of the present embodiment, the scanning light transmitted through the correction lens 45 is converted into two reflection mirrors 4.
Deflection to the photosensitive drum 56 by 8 and 50 is illustrated, but the present invention is not limited to the above-described embodiment, and the scanning light transmitted through the correction lens 45 is reflected by a single reflecting mirror (not shown). Biasing to 56 is also feasible.

Further, in the optical scanning device 18 of this embodiment,
Although the correction lens 45 whose rotation axis 58 is a straight line and is parallel to the main scanning direction as a whole has been illustrated, the present invention is not limited to the above embodiment. That is, the present invention is also applicable to an optical scanning device in which the shape error of the resin molding is reduced by bending only the central portion of the rotating shaft in parallel with the main scanning direction and bending both ends in the optical axis direction as described above. Is.

[0045]

As described above, the present invention rotatably supports the scanning mirror having the reflecting surface on which the emitted light of the laser light source is skew-incident, and the reflecting surface of the scanning mirror is negative in the main scanning direction. It is formed by a curved surface having power, a correction lens and a surface to be scanned are sequentially arranged on the main scanning optical path of this scanning mirror, and the surface to be scanned is positioned so as to be movable relative to the main scanning optical path in the sub-scanning direction. , The light incident surface of the correction lens is formed by a rotationally symmetric curved surface in which the rotation axis parallel to the main scanning direction is displaced from the center of the main scanning optical path in the sub-scanning direction and the envelope becomes an even-order higher-order curve. Since the light emitting surface of is formed by a rotationally symmetric curved surface in which the rotation axis orthogonal to the main scanning direction and the sub scanning direction is located at the center of the main scanning optical path and the envelope is an even-order higher-order curve, Optical aberration can be reduced and main scanning is performed in the stray light emission direction. Since it is possible to away from the road and has the effect of such optical property can be obtained a good optical scanning device.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing an internal structure of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional plan view showing a state in which a housing of the optical scanning device is partially broken.

FIG. 3 is an exploded perspective view showing an assembly structure of a main part of the optical scanning device.

FIG. 4 is a vertical sectional side view showing the shape of a correction lens.

FIG. 5 shows the shape of a correction lens, (a) is a plan view,
(B) is a vertical side view.

6A and 6B show various optical aberrations of the optical scanning device, FIG. 6A is a characteristic diagram showing an fθ error, FIG. 6B is a characteristic diagram showing a main-scanning field curvature, and FIG. 6C is a sub-scanning field curvature. Characteristic diagram showing (d)
[Fig. 4] is a characteristic diagram showing scanning line curvature.

FIG. 7 is a perspective view showing a prior art optical scanning device previously filed by the applicant.

FIG. 8 is a schematic view showing an optical relationship of each part.

FIG. 9 is a plan view showing the shape of a correction lens.

FIG. 10 shows various optical aberrations of the optical scanning device, (a)
Is a characteristic diagram showing fθ error, (b) is a characteristic diagram showing main-scanning field curvature, and (c) is a characteristic diagram showing sub-scanning field curvature.
(D) is a characteristic diagram showing scanning line curvature.

[Explanation of symbols]

 18 Optical Scanning Device 24 Laser Light Source 28 Scanning Mirror 42 Reflecting Surface 45 Correction Lens 34 Light Incident Surface 35, 39 Rotation Axis 38 Light Emitting Surface

Claims (1)

[Claims] 1. A scanning mirror having a reflecting surface on which light emitted from a laser light source is skew-incident is rotatably supported, and the reflecting surface of the scanning mirror is formed by a curved surface having a negative power in a main scanning direction, A correction lens and a surface to be scanned are sequentially arranged on the main scanning optical path of the scanning mirror, and the surface to be scanned is positioned so as to be movable relative to the main scanning optical path in the sub-scanning direction. The surface is formed by a rotationally symmetrical curved surface whose rotational axis parallel to the main scanning direction is displaced from the center of the main scanning optical path in the sub-scanning direction so that the envelope becomes an even-order higher-order curve, and the light exit surface of the correction lens The optical scanning device is characterized in that the rotational axis orthogonal to the main scanning direction and the sub-scanning direction is located at the center of the main scanning optical path, and the envelope is a rotationally symmetric curved surface having an even-order higher-order curve. .