JPH0750258B2 - Optical beam scanning device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device for scanning a surface to be scanned by deflecting a light beam from a light source with a deflector.

2. Description of the Related Art Conventionally, in a light beam scanning device using a deflector having a deflecting / reflecting surface, for example, a rotary polygon mirror, a light beam deflected and scanned by tilting of the deflecting / reflecting surface changes in a plane perpendicular to the scanning surface. There are various known light beam scanning devices that do not cause pitch irregularity in scanning lines on the surface to be scanned. For example, in JP-A-56-36622 and JP-A-57-144516, a light source for obtaining a light beam collimated with a laser light source into an appropriate beam diameter by an appropriate means, a linear image forming unit First imaging optical system consisting of a plano-convex cylindrical lens, and a single spherical lens and a single toric surface for imaging the light beam deflected in the vicinity of its linear imaging position on the surface to be scanned The second imaging optical system is composed of a lens. The deflective reflecting surface and the surface to be scanned have a geometrical-optical conjugate relationship in a plane perpendicular to the scanning direction, and the tilt of the deflective reflecting surface is optically corrected to correct the pitch unevenness of the scanning line.

However, in the conventional light beam scanning device, the F number in the scanning direction is as large as 60 and the F number in the direction perpendicular to the scanning direction is as large as 100, and the spot diameter of the light beam on the surface to be scanned is large. It is about 100 μm, and only a resolution of about 10 dots per mm can be obtained. In order to obtain a small spot diameter, it is necessary to reduce the F-number and to perform sufficient aberration correction. However, in the conventional light beam scanning device, the power in the plane perpendicular to the scanning direction of the second imaging optical system is In order to satisfy the geometrical optics conjugate relation, it becomes inevitably strong, large aberration is likely to occur, and it is difficult to reduce the F number.

In order to solve the above problems, in the light beam scanning device of the present invention, the first imaging optical system has the effect of converging light only in the direction perpendicular to the scanning direction, and the correction is further performed. The light-reflecting surface and the surface to be scanned have a geometrical-optical conjugate relationship in a direction perpendicular to the scanning direction, and the second imaging optical system is a deflector. In order from the side, a positive meniscus spherical lens with a concave surface facing the deflector side, a positive spherical lens with a convex surface facing the deflector side, and a lens having a toric surface are used in order to satisfy the following conditions. It is composed of.

3.8 <f _P / f _V <5.0 (1) 0.2f <L ₂ <0.4f (2) where f is the focal length of the entire system, and f _P and f _V are the second imaging optical system, respectively. Is the focal length in the scanning direction, the focal length in the direction perpendicular to the scanning direction, and L ₂ is the total lens length of the second imaging optical system.

In the second imaging optical system, since the deflective reflection surface and the surface to be scanned have a geometrical optical conjugate relationship in the direction perpendicular to the scanning direction, the power in the surface perpendicular to the scanning direction becomes the power in the scanning direction. It is stronger than that. Therefore, the spherical aberration in the direction perpendicular to the scanning direction is insufficiently corrected, and the reduction of the F number is greatly restricted by the residual aberration in making the optical system of the diffraction limited system. However, according to the present invention, since the first image forming optical system is constructed so as to have overcorrected spherical aberration, it is possible to mutually cancel out the uncorrected spherical aberration in the direction perpendicular to the scanning direction of the second image forming optical system. Fit. With the above operation, the residual aberration of the entire system is significantly reduced, and as a result, the optical beam scanning device of the present invention is
Therefore, it is possible to obtain a light beam scanning device capable of reducing the number and narrowing the spot diameter of the light beam on the surface to be scanned, which corresponds to high printing quality.

The condition (1) defines the ratio of the focal length in the deflection direction of the second imaging optical system to the focal length in the direction orthogonal to the deflection direction, and as f _P / f _V exceeds the lower limit, astigmatism is obtained. Is too large.

The condition (2) defines the total lens length of the second imaging optical system. Although it is advantageous for compactness in which L ₂ exceeds the lower limit, astigmatism becomes excessive and it becomes difficult to correct aberrations satisfactorily. When L ₂ exceeds the upper limit, the total length of the second imaging optical system becomes excessive, which Since the diameter of a lens having a toric surface also becomes large, it becomes difficult to reduce the cost.

Furthermore, it is desirable that the lens having the toric surface is a meniscus single lens having a positive power as a whole with a concave surface facing the deflector in a plane perpendicular to the scanning direction.

Furthermore, a lens having a toric surface is easy to process if r ₁₀ = ∞, where r ₁₀ is the radius of curvature related to the refraction in the scanning direction of the surface on the deflector side, and it is effective in reducing the cost. is there.

Embodiment An embodiment of the light beam scanning device according to the present invention will be described below. However, in each of the examples, r ₁ , r ₂ , ... Are the radii of curvature of the respective surfaces relating to refraction in the scanning direction in order from the light source, and r ₁ ′, r ₂ ′,. Curvature radii of each surface related to refraction, d ₁ , d ₂ , ... are surface spacings of the above surfaces, n ₁ , n ₂ ,
... is the refractive index of each lens at a wavelength of 790 nm.

An embodiment of a light beam scanning device according to the invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a schematic configuration diagram based on a first embodiment of a light beam scanning device according to the present invention. The output light from the laser light source is collimated by a collimator lens to have an appropriate beam diameter (not shown).
First, the light beam 1 is linearly imaged in the scanning direction in the vicinity of the deflective reflection surface 6 by the first imaging optical system 5 composed of two cylindrical lenses 2 and 3. The deflecting / reflecting surface 6 is one of a plurality of deflecting / reflecting surfaces provided around the rotary polygon mirror 7. This is rotationally driven by a motor (not shown) or the like to perform deflection. By the deflective reflection surface 6,
A scanning spot is formed on the surface 12 to be scanned. Where 2
As shown in FIG. 1, the spherical lenses 8 and 9 and the toric lens 10 have an outer shape so that at least a range through which the light beam passes can be secured so that the light beam scanning device can be downsized. desirable. 2 (a) and (b),
FIG. 3 is a schematic diagram showing a lens arrangement and an optical path in each scanning plane of the first embodiment, and a schematic diagram showing a lens arrangement and an optical path in a plane perpendicular to the scanning direction. As shown in FIG. 2B, in the plane perpendicular to the scanning direction with respect to the second imaging optical system 11, the deflective reflection surface 6 and the scanned surface 12 have a geometrical optical conjugate relationship, which is a so-called. It has a function of correcting the surface tilt of the deflective reflection surface. In the second imaging optical system having such an action, the power in the direction orthogonal to the scanning direction is larger than the power in the deflection direction, and spherical aberration that is undercorrected occurs in the direction orthogonal to the scanning direction. . In the present embodiment, as described above, the first image-forming optical system 5 formed by the cylindrical lens group has the overcorrected spherical surface so as to cancel the uncorrected spherical aberration generated in the second image-forming optical system. The aberration is generated in the direction perpendicular to the scanning direction. by this,
The spherical aberration in the entire system is significantly reduced. FIGS. 3, 4, 5, and 6 show the first embodiment and the second embodiment, respectively.
The characteristics in Examples, Third Example and Fourth Example are shown. In the figure, (a) is a spherical aberration in a direction perpendicular to the scanning direction of the first imaging optical system, (b) is a spherical aberration in a direction perpendicular to the scanning direction of the second imaging optical system, and (c) is the entire system. The spherical aberration in the direction perpendicular to the scanning direction, (d) indicates the astigmatism, the solid line indicates the sagittal (S) direction, and the broken line indicates the meridional (M) direction. (E) shows the linearity characteristic of scanning. As is clear from each figure, each residual aberration of the entire system is well corrected, and an optical beam scanning device having a small F number, a wide angle of view, and a surface tilt correction function is realized.

In the second and fourth embodiments, in the lens having the toric surface of the second imaging optical system, the radius of curvature r ₁₀ related to the refraction in the scanning direction of the deflector side surface is set to r ₁₀ = 0. This facilitates processing and reduces cost.

EFFECTS OF THE INVENTION According to the present invention, the first imaging optical system for linearly imaging the light beam from the light source in the vicinity of the deflective reflection surface is configured to have overcorrected spherical aberration, and further the second imaging The optical system comprises, in order from the deflector side, a negative meniscus spherical lens having a concave surface facing the deflector side, a negative spherical lens having a convex surface facing the deflector side, and a lens having a toric surface. By satisfying the condition (1), the present invention provides a light beam scanning device in which the residual aberration of the entire system is satisfactorily corrected, the F number is small, the angle of view is wide, and the surface tilt correction function is provided.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of a light beam scanning device based on the first embodiment of the present invention, FIG. 2 is a configuration diagram of the device of the first embodiment of the present invention, and FIG. 3 is a first embodiment. Characteristic diagram in
FIGS. 4, 5, and 6 are characteristic diagrams of the second, third, and fourth embodiments, respectively. 1 ... Light beam, 5 ... First imaging optical system, 6 ... Deflection / reflection surface, 11 ... Second imaging optical system, 12 ... Scanned surface.

Claims (2)

[Claims] 1. A first image forming a linear light beam from a light source.
An image forming optical system, a deflector having the deflection reflection surface near the position of linear image formation by the first image forming optical system, and a light beam deflected by the deflector via the second image forming optical system. In a light beam scanning device that scans a scanning surface, the first imaging optical system is configured to have a light converging effect only in a direction perpendicular to the scanning direction, and further to cause overcorrected spherical aberration.
With respect to the direction perpendicular to the scanning direction, the polarization reflection surface and the surface to be scanned have a geometrical optical conjugate relationship, and the second imaging optical system has a concave surface facing the deflector side in order from the deflector side. A light beam scanning device comprising three lenses, a negative meniscus spherical lens, a negative spherical lens having a convex surface facing the deflector side, and a lens having a toric surface, which satisfies the following conditions. 3.8 <f _P / f _V <5.0 (1) 0.2f <L ₂ <0.4f (2) However, f is the focal length in the deflection direction of the entire system, and f _P and f _V are the second connection. The focal length in the scanning direction of the image optical system, the focal length in the direction perpendicular to the scanning direction, and L ₂ are the total lens length of the second imaging optical system. 2. A lens having a toric surface, wherein r ₁₀ = ∞, where r ₁₀ is a radius of curvature relating to the refraction of the deflector side surface in the deflection direction. Light beam scanning device.