JP2000231073A - Optical scanning optical system having plate tilt correcting function and optical scanner using the system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cope with a system whose scanning length is long by providing an image-formation optical system consisting of three lenses including a lens having positive power only on its cross section in a subscanning direction on a side nearest to a surface to be scanned between a light deflecting reflection surface and the surface to be scanned and setting the absolute value of image- formation magnification of the cross section in the subscanning direction between them to 1 to 2. SOLUTION: This optical scanning optical system consists of a laser beam source 11, a collimating lens 12, a 1st image-formation optical system 1, a polygon mirror 14, a 2nd image-formation optical system 2 and the surface to be scanned 19. The optical system 2 consists of a 1st lens 16 being a toric lens having positive power on both surfaces, a 2nd lens 17 whose both surfaces are aspherical, and a 3rd lens 18 having the positive power only on its cross section in the subscanning direction in that order from the side of the light deflecting reflection surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning optical system having a surface tilt correcting function for forming an image by scanning a laser beam focused on a light-sensitive material surface, and an optical scanning apparatus using the same. The present invention relates to an optical scanning optical system having a surface tilt correction function corresponding to a system having a long scanning length exceeding the short side of the A3 size, and an optical scanning device using the same.

[0002]

2. Description of the Related Art Conventionally, a laser scanning optical system for forming an image by scanning a laser beam focused on a photosensitive material surface, a laser printer device using the optical system, and a laser plate making device are various types. It has been known.

[0003] Among them, as an optical scanning optical system having a so-called surface tilt correction function, for example, those described in Japanese Patent Application Laid-Open No. Hei 4-141819 and Japanese Patent Application Laid-Open No.
What is described in 5986 is known. Here, an optical scanning optical system having a surface tilt correction function is a first imaging optical system that linearly forms an image of a light beam from a light source on or near a light deflection reflection surface of a light deflection unit, and A second imaging optical system for forming an image of the light beam deflected by the light deflecting means on the surface to be scanned, wherein the light deflection reflecting surface and the surface to be scanned are optically substantially conjugated with respect to a cross section in the sub-scanning direction. It is configured so that

In the optical scanning optical system having the surface tilt correcting function described in the above-mentioned publication, the second imaging optical system is composed of two lenses, and the field curvature is small and the apparatus is compact. It is.

[0005]

However, the optical scanning optical system having the surface tilt correcting function and the optical scanning device using the optical scanning system have a relatively short scanning length of about A4 short side (210 mm). There is a problem that can only deal with.

[0006] Even if the scanning length is sufficiently long, it cannot be adopted in a system requiring high resolution.

That is, in the above-described optical scanning optical system having the surface tilt correction function and the optical scanning device using the same, the absolute value of the imaging magnification between the light deflection reflecting surface and the surface to be scanned in the cross section in the sub-scanning direction. The value is about 5 times larger. Therefore, when used in a system having a long scanning length or a system having a high resolution, it is difficult to form a uniform light spot on the surface to be scanned due to excessively large field curvature of the sub-scanning direction component (SAGITTAL). Become. Further, the asymmetry of the curvature of field caused by the oblique incidence of light on the light deflecting / reflecting surface is further enlarged on the surface to be scanned, so that the homogeneity of the light spot is reduced.

Further, since the displacement near the light deflecting / reflecting surface is enlarged, the position accuracy of the light deflecting means must be maintained at a high level.

If the second imaging optical system can be arranged at a distance from the light deflecting and reflecting surface and the surface to be scanned, the magnification can be reduced. However, in this case, if an attempt is made to correspond to a scanning length larger than the short side of the A4 size, each lens of the second imaging optical system becomes large. To rise.

The present invention has been made in view of the above circumstances, and reduces the curvature of field in the sub-scanning direction while considering the ease and cost of manufacturing a lens. By reducing the influence of the asymmetry of the curvature, A
An object of the present invention is to provide an optical scanning optical system having a surface tilt correction function capable of coping with a system exceeding a short side of three dimensions (297 mm) and an optical scanning device using the same.

[0011]

According to the present invention, there is provided an optical scanning optical system having a surface tilt correcting function, wherein a light beam from a light source is linearly imaged on or near a light deflecting reflection surface of a light deflecting means. And a second imaging optical system for forming an image of the light beam deflected by the light deflecting means on the surface to be scanned. The surface and the optically configured to be approximately conjugate,
In an optical scanning optical system having a surface tilt correction function, the second imaging optical system has a cross-sectional shape in the main scanning direction and a cross-sectional shape in the sub-scanning direction that are different from each other on both surfaces in order from the side of the light deflecting means. A first lens having a positive power in both the directional section and the sub-scanning direction section, a second lens having a non-circular sectional shape in the main scanning direction on both sides, and having substantially no power in the main scanning direction section, And a third lens having a positive power in the cross section in the sub-scanning direction.

The first lens has a non-circular cross-sectional shape in the main scanning direction on the surface on the side of the light deflecting means, and the second lens has a second circular shape.
It is preferable that both surfaces of the third lens are rotationally symmetric aspherical surfaces, and that the third lens is a cylindrical lens in which the cross-sectional shape in the main scanning direction is a straight line orthogonal to the optical axis on both surfaces.

Preferably, the material of each of the first to third lenses is a resin.

It is preferable that the following conditional expression is satisfied.

[0015] _{1.0 <f 3V / f V <} 1.6 However, _{f V:} focal length in the sub scanning cross section of the second imaging optical system f _3V: focal length in the sub scanning cross section of the third lens

An optical scanning device according to the present invention is characterized by using an optical scanning optical system having a surface tilt correcting function according to the present invention.

Here, the "main scanning direction" means a direction parallel to the trajectory of the deflected light beam on the surface to be scanned, and the "sub-scanning direction" means the main scanning direction on the surface to be scanned. Means a direction substantially perpendicular to the direction. The “section in the main scanning direction” means a section in the main scanning direction including the optical axis, and the “section in the sub-scanning direction” means a section perpendicular to the section in the main scanning direction and including the optical axis.

The above-mentioned "non-circular arc" means a line shape which is not a circular arc in a predetermined cross section, and the above-mentioned "aspherical surface" means a rotationally symmetric surface obtained by rotating the non-circular arc about the optical axis as a rotation axis. Mean shape.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the configuration of an optical scanning optical system according to an embodiment of the present invention.

As shown in FIG. 1, this optical scanning optical system comprises:
A collimating lens 12 that converts a light beam emitted from a laser light source 11 into substantially parallel light, a first imaging optical system 1 that linearly forms the substantially parallel light into an image in the main scanning direction,
The light deflecting / reflecting surface 15 is located near the image forming position of the image forming optical system 1.
A polygon mirror 14 which is a light deflecting means for reflecting and deflecting the light beam to scan on the surface to be scanned 19, and for reflecting the light beam reflected and deflected by the polygon mirror 14 on the surface to be scanned 1
The light beam is focused on the surface to be scanned 19 at a substantially constant speed.
And a second imaging optical system 2 acting to scan upward.

Here, the first image forming optical system 1 includes a cylindrical lens 13 having a positive refractive power in the sub-scanning direction for forming a light beam into a linear image.

Next, the second imaging optical system will be described with reference to FIG. FIG. 2 shows a configuration of a second imaging optical system of the optical scanning optical system according to the embodiment of the present invention,
(A) is a schematic view in a section in the main scanning direction including the optical axis (hereinafter, referred to as a section in the main scanning direction), and (B) is a section perpendicular to the section in the main scanning direction and including the optical axis (hereinafter, a section in the sub-scanning direction). FIG.

As shown in FIG. 2, the second imaging optical system 2 has a non-circular cross section in the main scanning direction on the surface on the light deflecting means side in the order from the light deflecting / reflecting surface side. The first lens 16 is a toric-like lens having different shapes and cross-sectional shapes in the sub-scanning direction from each other, and both surfaces have positive power in both the main-scanning direction cross-section and the sub-scanning direction cross-section. A second lens 17 and a cylindrical lens whose main surface in the main scanning direction has a straight line perpendicular to the optical axis on both surfaces. The second lens 17 has almost no power in the main scanning direction and has a positive power in the sub-scanning direction. And a third lens 18 having power.

Here, the first to third lenses 16 to 18 are made of resin, and the second imaging optical system 2 satisfies the following conditional expression.

[0026] _{1.0 <f 3V / f V <} 1.6 However, _{f V:} second focal length in the sub scanning cross section of the imaging optical system 2 f _3V: focal length in the sub scanning cross section of the third lens 18

In FIG. 1, the light beam emitted from the laser light source 11 is transmitted to the second imaging optical system 2 by the polygon mirror 14 rotating in the direction of arrow A, so that the light beam And the scanned surface 19
The main scanning is performed at a substantially constant speed. Further, the scanned surface 1
9 is moved in the sub-scanning direction (the direction of arrow B), and an image is formed by modulating light. The light deflecting / reflecting surface 15 and the surface to be scanned 19 have a conjugate relationship with the second imaging optical system 2 in the cross section in the sub-scanning direction, thereby optically correcting the inclination of the light deflecting / reflecting surface 15. Function can be obtained.

Note that the direction of sub-scanning is the relative movement direction between the surface to be scanned 19 and the scanning light beam, and the surface to be scanned 19 may be fixed and the scanning light beam may be moved.

Since the second imaging optical system 2 has the above-described three-element configuration, the power of each lens in the cross section in the sub-scanning direction can be shared by the third lens 18. Since the third lens 18 is located closer to the surface to be scanned 19 than the other two lenses, by sharing the power in the cross section in the sub-scanning direction to the third lens 18,
The second imaging optical system 2 can reduce the absolute value of the imaging magnification β between the light deflecting reflection surface 15 and the surface to be scanned 19 with respect to the cross section in the sub-scanning direction to about 1 to 2 times.

Thus, the sub-scanning direction component (SAGIT
TAL) can be reduced, and the asymmetry of the curvature of field on the light deflecting / reflecting surface 15 is less likely to expand. Therefore, the optical scanning device having a longer scanning length than the short side of A3 size (297 mm). A uniform light spot can be formed on the surface to be scanned.

Further, the present invention can be applied to an optical scanning device requiring high resolution.

Further, since the displacement near the light deflecting / reflecting surface is unlikely to be enlarged, the tolerance for the positional accuracy of the light deflecting means can be increased.

Although the number of components is increased by forming the three second imaging optical systems 2 in this manner, the first lens 16 and the second lens 17 do not need to be large lenses. Further, it is possible to maintain the ease of manufacturing the lens and suppress an increase in cost. Further, the third lens 18 is a cylindrical lens having a positive power only in the cross section in the sub-scanning direction, and is excellent in ease of lens production and cost. In addition, a lightweight and inexpensive lens can be obtained by using a resin material for the three lenses.

Further, the conditional expression relating to f _3V / f _V is defined by the second imaging optical system 2 and the third imaging optical system in the section in the sub-scanning direction.
The ratio of the focal length to the lens 18 is specified. As described above, the power of the second imaging optical system 2 is transferred to the third lens 18.
To the light deflecting / reflecting surface 15 and the surface 1 to be scanned.
9, the absolute value of the imaging magnification β in the sub-scanning direction in the sub-scanning direction can be made 1 to 2 times, so that a predetermined condition is preferably set for the power distribution ratio to the third lens 18. If the lower limit of this conditional expression is exceeded, the position of the third lens 18 will be too close to the surface to be scanned 19, making it difficult to dispose the second imaging optical system 2 in the optical scanning optical system. The third lens 18 becomes longer in the main scanning direction. When the value exceeds the upper limit of this conditional expression, the above-mentioned imaging magnification β becomes too large.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical scanning optical system having a surface tilt correcting function and an optical scanning device using the same according to the present invention, and in particular, a second imaging optical system 2 which is a feature of the optical scanning optical system will be described in detail. This will be described using specific numerical values.

<Embodiment 1> The configuration of an optical scanning optical system having a surface tilt correction function according to Embodiment 1 is as described above in the embodiment, but the focal length of the collimating lens 12 is 17 mm, The focal length of the lens 13 is
It is 59 mm.

The radii of curvature R _H and R _V of each lens surface of the second imaging optical system 2 in the first embodiment (where R _H is the radius of curvature in the cross section in the main scanning direction, and R _V is the radius of curvature in the cross section in the sub scanning direction) And the unit of the radius of curvature is mm. The same applies to the following embodiments.), The lens interval (or lens thickness) D (mm) of each lens, and the refractive index N of each lens at a wavelength of 780 nm. It is shown in the upper row of Table 1. However, in Table 1 and the tables described later, each symbol R,
The numbers corresponding to D and N are sequentially increased from the light deflection reflection surface side. Also, the radii of curvature _RH and _RV are
As will be described later, when the lens surface is a surface having a non-circular cross section in the main scanning direction or an aspheric surface, it is a numerical value of a radius of curvature near the optical axis.

[0038]

[Table 1]

Here, each lens surface will be described.

In each lens surface, the non-circular shape or the aspherical shape of the surface having a non-circular shape in a predetermined cross section is represented by the following non-circular / aspherical expression. This non-circular arc / aspherical surface expression is the same in the non-circular arc shape and the aspherical surface shape in the following embodiments.

[0041]

(Equation 1)

In the middle part of Table 1 above, each coefficient 1 / R, K, A ₄ , A ₆ , A ₈ , A of each non-circular arc / aspheric surface shown in the non-circular arc / aspheric surface formula in the first embodiment. A value of ₁₀ is shown.

The first surface, that is, the surface of the first lens 16 on the light deflecting / reflecting surface side is a non-circular arc on the cross section in the main scanning direction represented by the above-mentioned non-circular / aspherical expression and each coefficient. A rotation axis is a straight line perpendicular to the optical axis in the same cross section including a point separated by a radius of curvature R _V1 on the optical axis from a point intersecting with the optical axis, and has a shape formed by rotation.

The second surface, that is, the surface of the first lens 16 on the side to be scanned has a circular arc having a radius of curvature R _V2 and a point separated from the point where the circular arc intersects the optical axis by a radius of curvature R ₂ on the optical axis. And a straight line perpendicular to the cross section in the main scanning direction is used as a rotation axis, and has a shape formed by rotation.

Both surfaces of the second lens 17, that is, the third surface and the fourth surface have an aspherical shape which is rotationally symmetric with respect to the optical axis as shown in the above-mentioned aspherical / aspherical expression and each coefficient.

The third lens 18 is a cylindrical lens having power only in the section in the sub-scanning direction.
The surface (fifth surface) on the light deflection / reflection surface side is a cylindrical surface having a positive power only in the sub-scanning direction,
Plane) is a plane.

The lower part of Table 1 shows the distance D ₀ (mm) from the light deflecting reflection surface 15 of the first embodiment to the light deflecting reflection surface side of the first lens 16, and the second imaging optical system 2. Focal length f
(Mm), the half angle of view θ of the optical scanning optical system according to the first embodiment,
The wavelength λ (nm) of the laser light source 11, the magnification β _{V of} the cross section in the sub-scanning direction between the light deflection reflecting surface 15 and the surface to be scanned 19, and the value f _3V / f _V of the conditional expression are shown.

Embodiment 2 The configuration of an optical scanning optical system having a surface tilt correcting function according to Embodiment 2 is substantially the same as that of Embodiment 1, except that the focal length of the cylindrical lens 13 is 33 m.
m.

In the second embodiment, the shapes of the first to sixth lens surfaces of the second imaging optical system 2 are formed in the same manner as in the first embodiment.

In the second embodiment, the radii of curvature R _H and R _V of each lens surface of the second imaging optical system 2, the lens interval (or lens thickness) D (mm) of each lens, and the wavelength 780 nm of each lens Are shown in the upper part of Table 2. However, the radii of curvature R _H and R _V are numerical values of the radii of curvature near the optical axis when the lens surface is a surface having a non-circular cross section in the main scanning direction or an aspheric surface.

In the middle part of Table 2, each coefficient 1 / R, K, A ₄ , A ₆ , A ₈ , of each aspherical arc / aspherical surface shown in the aspherical / aspherical surface equation in the second embodiment is shown. indicates the value of the a _10, the lower part of Table 2, the distance D from the light deflection reflecting surface 15 of the second embodiment to the surface of the light deflection reflecting surface of the first lens 16
₀ (mm), the focal length f (m) of the second imaging optical system 2
m), the half angle of view θ of the optical scanning optical system according to the second embodiment, the wavelength λ (nm) of the laser light source 11, and the magnification β _{V of the} cross section in the sub-scanning direction between the light deflection reflecting surface 15 and the surface to be scanned 19. And the value of the conditional expression f _3V / f _V are shown below.

[0052]

[Table 2]

Embodiment 3 The configuration of an optical scanning optical system having a surface tilt correcting function according to Embodiment 3 is substantially the same as that of Embodiment 1.

In the third embodiment, the first to sixth lens surfaces of the second imaging optical system 2 are formed in the same manner as in the first embodiment.

In Embodiment 3, the radii of curvature R _H and R _V of each lens surface of the second imaging optical system 2, the lens interval (or lens thickness) D (mm) of each lens, and the wavelength 780 nm of each lens Are shown in the upper part of Table 3. However, the radii of curvature R _H and R _V are numerical values of the radii of curvature near the optical axis when the lens surface is a surface having a non-circular cross section in the main scanning direction or an aspheric surface.

In the middle part of Table 3, each coefficient 1 / R, K, A ₄ , A ₆ , A ₈ , of each aspherical arc / aspherical surface shown in the aspherical / aspherical surface equation in the third embodiment is shown. indicates the value of the a _10, the lower part of Table 3, the distance D from the light deflection reflecting surface 15 of the third embodiment to the surface of the light deflection reflecting surface of the first lens 16
₀ (mm), the focal length f (m) of the second imaging optical system 2
m), the half angle of view θ of the optical scanning optical system according to the third embodiment, the wavelength λ (nm) of the laser light source 11, and the magnification β _{V of the} cross section in the sub-scanning direction between the light deflection reflecting surface 15 and the surface to be scanned 19. And the value of the conditional expression f _3V / f _V are shown below.

[0057]

[Table 3]

FIGS. 3 to 5 show aberration diagrams (views of field curvature and distortion) of the optical scanning optical system having the surface tilt correcting function according to the first to third embodiments. As apparent from FIGS. 3 to 5, according to each of Examples 1 to 3, it is apparent that each aberration including the curvature of field in the sub-scanning direction is good.

The optical scanning optical system having the surface tilt correcting function of the present invention and the optical scanning device using the optical scanning optical system are not limited to those of the above-described embodiment, but various modifications can be made. For example, the radii of curvature R _H and R _{V of} each lens
In addition, the lens interval (or lens thickness) D can be appropriately changed.

The first lens 16 of the second imaging optical system 2 has a non-circular cross section in the main scanning direction on the surface on the side of the light deflecting means. It is a toric-like lens having a different cross-sectional shape, and has a positive power in both the main scanning direction cross-section and the sub-scanning direction cross-section. It is not necessary.

The second lens 17 in the second imaging optical system 2 is a lens having both surfaces formed of rotationally symmetric aspherical surfaces, but one or both surfaces have a non-sectional shape in the main scanning direction. The lens may be an arc.

The third lens 18 in the second imaging optical system 2 is a cylindrical lens. However, the third lens 18 is not limited to a cylindrical lens, has almost no power in a cross section in the main scanning direction, and has no power in the sub scanning direction. A lens having a positive power in the cross section may be used.
A concave cylindrical mirror having little power in the cross section in the main scanning direction and having positive power in the cross section in the sub scanning direction may be used.

[0063]

As described above, according to the optical scanning optical system having the surface tilt correcting function of the present invention, the configuration of the second imaging optical system disposed between the light deflection reflecting surface and the surface to be scanned. A first lens having a cross section in the main scanning direction and a cross section in the sub scanning direction that are different from each other on both sides in order from the light deflection reflection surface side, and both having a positive power in the cross section in the main scanning direction and the sub scanning direction. A three-lens configuration has a second lens having a non-circular cross section in the main scanning direction on both surfaces, and a third lens having almost no power in the main scanning direction cross section and having positive power in the sub scanning direction cross section. Thus, the light deflection / reflection surface 15 with respect to the section in the sub-scanning direction
The absolute value of the imaging magnification β between the image and the scanned surface 19 can be reduced to about 1 to 2 times.

Therefore, it is possible to reduce the curvature of field of the component in the sub-scanning direction while securing the ease and cost of manufacturing the lens, and it is difficult to increase the asymmetry of the curvature of field on the light deflection reflecting surface. A3 short side (297mm)
It can be applied to optical scanning devices with long scanning lengths

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical scanning optical system according to an embodiment of the present invention.

FIGS. 2A and 2B are a sectional view in a main scanning direction and a sectional view in a sub-scanning direction showing a configuration of a second imaging optical system of the optical scanning optical system according to the embodiment of the present invention;

FIG. 3 is an aberration curve diagram of the optical scanning optical system according to the first embodiment.

FIG. 4 is an aberration curve diagram of the optical scanning optical system according to the second embodiment.

FIG. 5 is an aberration curve diagram of the optical scanning optical system according to the third embodiment.

[Explanation of symbols]

R _{H1 to} R _{H6 The} radius of curvature of the lens surface in the main scanning direction R _{V1 to} R _{V6 The} radius of curvature of the lens surface in the sub scanning direction D _{0 to} D ₅ Lens surface spacing (lens thickness) 1 First imaging optical system 2 Second Imaging optical system 11 Laser light source 12 Collimating lens 13 Cylindrical lens 14 Polygon mirror 15 Light deflection / reflection surface 16 First lens 17 Second lens 18 Third lens 19 Scanned surface

Claims (5)

[Claims] 1. A first imaging optical system for linearly forming an image of a light beam from a light source on or near a light deflecting reflection surface of a light deflecting device, and scanning the light beam deflected by the light deflecting device. A second image-forming optical system for forming an image on a surface, wherein the light deflection reflecting surface and the surface to be scanned are optically substantially conjugate with respect to a cross section in the sub-scanning direction, In the optical scanning optical system having a function, the second imaging optical system has a main scanning direction cross-sectional shape and a sub-scanning direction cross-sectional shape different from each other, and A first lens having a positive power in both cross sections in the sub-scanning direction, a second lens having a non-circular cross-sectional shape in the main scanning direction on both surfaces; Positive in section Tilt the optical scanning optical system having a correction function to Jicho to be composed of a third lens having a word. 2. The first lens has a non-circular cross section in the main scanning direction on a surface on the side of the light deflecting means, the second lens has an aspheric surface whose both surfaces are rotationally symmetric, and the third lens has a third surface. 2. The optical scanning optical system having a surface tilt correcting function according to claim 1, wherein the lens is a cylindrical lens having a cross section in the main scanning direction on both surfaces thereof being a straight line orthogonal to the optical axis. 3. The optical scanning optical system according to claim 1, wherein the first to third lenses are made of resin. 4. An optical scanning optical system having a surface tilt correction function according to claim 1, wherein the following conditional expression is satisfied. _{1.0 <f 3V / f V <} 1.6 However, _{f V:} focal length in the sub scanning cross section of the second imaging optical system f _3V: focal length in the sub scanning cross section of the third lens 5. An optical scanning device using the optical scanning optical system having a surface tilt correction function according to claim 1. Description: