JPH0261608A - Scan optical system with surface tilt correction - Google Patents

Abstract

PURPOSE:To reduce the cost and facilitate the adjustment by composing a linear image formation optical system of a single lens which is convex on its light source side at right angles to a scanning surface and symmetrically convex on its deflector side about the optical axis. CONSTITUTION:A laser scanning device consists of a semiconductor laser 1 as a light source, the linear image formation optical system 2, a polygon mirror 3, and ftheta lens 4, a photosensitive drum 5, etc. Then the linear image formation optical system 2 consists of the single lens which is convex on the side of the light source 1 at right angles to the scanning surface and symmetrically convex on the side of the deflector 3 about the optical axis. Namely, nearly parallel luminous flux is obtain in the scanning surface direction and a linear image is formed on the deflector 3 at right angles to the scanning surface. Consequently, the cost is reduced greatly and the adjustment is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface tilt correction scanning optical system that is mainly used in laser beam printers and the like and eliminates pitch unevenness in the sub-scanning direction of scanning lines.

More specifically, there is a linear imaging optical system that forms a linear image of a beam of light emitted from a light source onto a deflection/reflection surface of a deflector, and a linear imaging optical system that forms a linear image of a beam of light emitted from a light source onto a deflection/reflection surface of a deflector, and a beam of light reflected and deflected by the deflector onto an object to be scanned. The present invention particularly relates to the linear imaging optical system described above in a surface tilt correction scanning optical system including a scanning imaging optical system that forms an image.

[Prior Art] Laser beam printers have the advantage of being able to perform recording at extremely high speeds, and in recent years, they have gradually become smaller and lower in cost. With the diversification and development of pottery, the demand for it is increasing.

Next, such a laser beam printer will be explained with reference to FIG.

A laser beam B directly modulated according to image information from a semiconductor laser l as a light source is converged in a direction perpendicular to the scanning plane by a linear imaging optical system 2, and is deflected and reflected by a polygon mirror 3 as a deflector. A linear image is formed on the surface 3a.

The laser beam B reflected by this deflection reflecting surface 3a is deflected as the polygon mirror 3 rotates, and is imaged on the photoreceptor drum 5 by an fθ lens 4 which is a scanning imaging system.
It is configured to scan in six directions.

In such a laser beam printer, the deflection reflection surface 3a of the deflector such as the polygon mirror 3 used to scan the beam B from the light source 1 may be affected by manufacturing errors, installation errors, vibrations during rotation, etc. , there is some inclination error in the direction perpendicular to the scanning plane.

Therefore, the beam B reflected by the deflection reflecting surface 3a having such a tilt error shifts the image formation position on the object to be scanned in the sub-scanning direction, resulting in uneven scanning line pitch. This unevenness in the pitch of the scanning lines causes a deterioration in the image quality of recording, for example in a recording apparatus such as a laser beam printer.

The above-mentioned surface tilt correction scanning optical system is intended to eliminate such pitch unevenness of the scanning line, and once the beam B from the light source 1 is directed to the direction perpendicular to the scanning plane by the linear imaging optical system 2. Converging and forming a linear image on the deflection reflection surface 3a of the deflector, restoring the light beam from the deflection reflection point in this direction by a scanning imaging optical system and forming a conjugate image on the object to be scanned. This is to avoid being affected by the tilting error of the deflection reflecting surface 3a.

In this specification, the term "scanning plane" refers to a plane formed by a time-series collection of light beams to be scanned, that is, the main scanning line on the object to be scanned, and the plane of this surface tilt correction scanning optical system. It shall mean a plane that includes the optical axis.

[Problems to be Solved by the Invention] Conventionally, in such a scanning optical system, a linear imaging optical system for a light source with a large divergence angle, such as a semiconductor laser, first passes a beam of light emitted from a light source through a collimator. A light beam is made approximately parallel to the lens, and then a linear image is formed on a deflection and reflection surface by a cylindrical lens having positive refractive power in a direction perpendicular to the scanning plane.

In this case, it may depend on the size of the divergence angle of the light source and the proportion of the light beam taken in by the collimator lens, but the collimator lens usually requires a lens system consisting of 2 to 4 lenses, and a cylindrical lens may also be arranged. A linear imaging optical system is constructed.

SUMMARY OF THE INVENTION The present invention provides an optical system for correcting surface inclination, which aims to significantly reduce costs by configuring a linear imaging optical system using only the simplest single lens, and further simplifies adjustment.

[Means and effects for solving the problem] The linear imaging optical system of the scanning optical system for surface tilt correction according to the present invention has a convex surface on the light source side in a direction perpendicular to the scanning surface, and a convex surface on the deflector side in the direction perpendicular to the scanning surface. It is characterized by being composed of a single lens with a convex surface.

In the linear imaging optical system according to the present invention, the light beam emitted from the light source is formed so that the surface on the light source side is a convex surface in a direction perpendicular to the scanning direction, and the surface on the deflector side is a convex surface symmetrical to the optical axis.
The light beam is substantially parallel in the scanning plane direction, and a linear image is formed on the deflector in the direction perpendicular to the scanning plane direction.

If the divergence angle of the light source is large and a large amount of the light beam emitted from the light source is to be captured, it is desirable to reduce aberrations by making the surface on the deflector side a convex aspherical surface symmetrical to the optical axis.

Further, it is desirable that the surface on the light source side be an aspherical surface that is convex in a direction perpendicular to the scanning direction to better correct aberrations in this direction.

The NA' in the direction perpendicular to the scanning plane of the light beam that forms a linear image on the deflector surface is the divergence angle of the light source in this direction.

The ratio of the captured luminous flux, the final spot diameter on the scanned object, and the magnification in the direction perpendicular to the scanning plane of the scanning optical system (
That is, due to surface tilt correction, the deflection point and the object to be scanned have a substantially conjugate relationship in this direction, and this refers to the imaging magnification. ), but if this NA' is large, the surface on the light source side is made an aspherical surface that is convex in the direction perpendicular to the scanning direction.

Is it necessary to reduce aberration in this direction?

That is, in the direction perpendicular to the scanning direction, the convex aspherical surface (optical axis symmetry) on the light source side corresponds to the convex aspherical surface (optical axis symmetry) on the polarizer side.
A larger NA can be achieved by determining the
”, the above linear imaging system is obtained.

In this way, the linear imaging optical system can be configured with only a single lens, making it possible to significantly reduce costs and simplify adjustment.

In particular, in terms of cost reduction, for example, if the lens is manufactured by a manufacturing method such as direct pressing, the effect will be very large.

[Example] Hereinafter, an example of the present invention will be specifically described based on the drawings. The surface tilt correction scanning optical system according to the present invention is an optical system used, for example, in a laser scanning device such as a laser beam printer.

As shown in FIG. 7, the laser scanning device includes a semiconductor laser 1 as a light source, a linear imaging optical system 2. polygon mirror 3
．． It is composed of an fθ lens 4, a photoreceptor drum 5, and the like.

A laser beam B that is directly modulated according to one-screen information is emitted from the semiconductor laser 1, and this laser beam B, which is an example of a beam bundle, is linearly converged by the linear imaging optical system 2, and is focused by the deflector. An image is formed on a deflection reflection surface 3a of a polygon mirror 3, which is an example. The laser beam B reflected by the deflection reflecting surface 3a is deflected as the polygon mirror 3 rotates, and is imaged on the photoreceptor drum 5 by an fθ lens 4, which is an example of a scanning imaging optical system. The image is scanned in the direction shown in the figure.

The surface tilt correction scanning optical system mainly consists of the above-mentioned linear imaging optical system 2 and scanning imaging optical system 4, and corrects the pitch deviation of the scanning line caused by the surface tilt of the deflection reflecting surface 3a of the deflector 3. It is to be removed.

Tables 2 and 3 show the specifications of Example 1 and Example 2 representing the specific configuration of the linear imaging optical system 2 according to the present invention.

There are two examples, respectively shown in Fig. 1 and Fig. 2.
The lens configuration diagram is shown in the figure, and the aberration curve diagrams are shown in FIGS. 3 to 6. Table 1 below summarizes their correspondence.

Table 1 Table 2 f = IO, N, 8, -0, 2 (light source side) curvature 'f - diameter
Radius of curvature・Axis spacing Refractive indexIn each lens component section, (A) shows the lens arrangement cut along the scanning plane, and (B) shows the lens arrangement cut along the plane perpendicular to the scanning plane. They are shown below.

The aberration curves in each aberration diagram are evaluated on the light source plane by tracing them in a direction opposite to the direction in which the light beam actually travels.

That is, 1st. After passing through the optical system, the light beams emitted from the two light sources in the second embodiment become parallel light beams in the direction along the scanning plane, and form an image in the direction perpendicular to the scanning plane.

"1' Cylindrical force Drill aspherical surface a 4-0.6 go 324 X In-'
a 6- 0.15252 X lff-'
r2 ■ Aspherical surface a 4 + 0.47 old co X 10-co
a6 + 0.21518 x 10-' (-6,691 mm from the light source r) (120 m5 from the imaging position in the direction perpendicular to the scanning plane)
However, for an aspherical shape, the X coordinate is taken in the direction of the optical axis, and the Y coordinate is taken in the direction perpendicular to the optical axis.

(Leaving space below) a+: JF spherical coefficient Table 3 f = IO, N, ^, at 0.25 (Light source side) Radius of curvature radius of curvature axis upper surface interval Refractive index rI' Cylindrical aspherical surface a4-0.41171 X 10- ' aa
+ 0.751HX 10-' 2° aspherical surface a4 + 0.48576 x 10-' aa
+ 0.22954 x 10-' (light source is ', -8,015 m) (100110 m from the imaging position in the direction perpendicular to the scanning plane)
0l1 L,, When the aspherical shape is taken with the X coordinate in the direction of the optical axis and the Y coordinate in the direction perpendicular to the It is also possible to configure a linear imaging optical system as a deviation correction scanning optical system. Moreover, it is possible to form an extremely clear scanning optical system without any deterioration in performance.

[Brief explanation of the drawing]

The drawings show an embodiment of the surface tilt correction scanning optical system according to the present invention, and FIG. 1 (A), (B) and FIG. 2 (A), (B).
1(A) and 2(A) are lens configuration diagrams of the example.
Figure (A) is a lens configuration diagram cut in the direction along the scanning plane, Figures 1 (B) and 2 (B) are lens configuration diagrams cut in the direction perpendicular to the scanning plane, and Figures 3 to 3. Figure 4 is an aberration diagram in the direction along the scanning plane in each example. Figures 5 and 6 are aberration diagrams in the direction along the scanning plane in each example. Figure 7 is an aberration diagram in the direction along the scanning plane in each example. FIG. 2 is a schematic diagram of the device. l ・ 2 ・ 3 ・ a 4 ・ 5 ・ B

Claims (2)

[Claims] (1) A linear imaging optical system that forms a linear image of the light beam emitted from the light source on the deflection reflection surface of a deflector, and forms an image of the light beam reflected and deflected by the deflector onto the object to be scanned. A scanning optical system for surface tilt correction, wherein the linear imaging optical system has a convex surface on the light source side in a direction perpendicular to the scanning surface, and a convex surface on the deflector side that is symmetrical to the optical axis. A surface tilt correction scanning optical system characterized by being composed of a single lens. (2) The linear imaging optical system is characterized by being composed of a single lens whose light source side is a convex aspherical surface in a direction perpendicular to the scanning plane, and whose deflector side is a convex aspherical surface symmetrical to the optical axis. The surface tilt correction scanning optical system according to claim 1.