JPH01200219A - Light beam scanning optical system - Google Patents

Abstract

PURPOSE:To make an optical system compact without using expensive f.theta lenses by interposing a spherical mirror in the optical path from a deflector to the surface of a photosensitive body so that a specific formula is satisfied and uniformly correcting the scanning speed in the main scanning direction. CONSTITUTION:A semiconductor laser 1 emits a divergent luminous flux carrying the intensity modulated picture information by a control circuit. This divergent luminous flux is corrected to parallel rays of a luminous flux by a collimator lens 5 and is continuously reflected on the surface of a polygonal mirror 10 and is scanned at a uniform angular speed. This scanned luminous flux passes a beam splitter 15 and is reflected on the concave of a spherical mirror 20 and is reflected on the beam splitter 15 again and is condensed on a photosensitive body 30. Since relations between a distance (d) from a point 10a, where the luminous flux is reflected toward the center of the scan area by the mirror 10, to an apex 20a of the spherical mirror 20 and a radius RM of curvature of the spherical mirror 20 are set to satisfy 0.15<(d/¦RM¦)<0.45, the scanning speed in the main scanning direction is uniformly corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a light beam scanning optical system, particularly a light beam that is incorporated into a laser beam printer, facsimile, etc., and focuses a light beam carrying image information onto a photoreceptor. Regarding the structure of a scanning optical system.

Conventional technology and its challenges In general, light beam scanning optical systems used in laser beam printers and facsimile machines basically consist of a semiconductor laser as a light source, a polygon mirror, and a galvano mirror.
It is composed of a deflector such as, and an rθ lens. A deflector scans the light beam emitted from a semiconductor laser at a constant angular velocity, and if left as is, there will be a difference in scanning speed from the center in the main scanning direction to both ends of the light condensing surface, making it impossible to obtain a uniform image. . The rθ lens is installed to correct such a difference in scanning speed.

By the way, the fθ lens is a combination of various concave lenses, convex lenses, etc., and the lens design is extremely complicated.
The number of surfaces to be polished is large, making it difficult to improve machining accuracy, and it is also expensive. Moreover, there are also constraints from the material standpoint, such as the need to select a material with good translucency.

Therefore, conventionally, an ellipsoidal mirror is used instead of the rθ lens (Japanese Patent Laid-Open No. 123040/1983).
, using a parabolic mirror (Special Publication No. 55-3612)
7), using a concave reflecting mirror (Japanese Patent Application Laid-open No. 1983-
173212) has been proposed. However, ellipsoidal mirrors and parabolic mirrors have a problem in that it is difficult to process them and to improve their processing accuracy. In addition, in those that use a concave reflector, the reflected light is focused in a direction perpendicular to the photoreceptor surface, so it is necessary to use a concave reflector with the same length as the main scanning direction, and the optical system The problem is that the size itself becomes impractically large.

Therefore, an object of the present invention is to adopt a scanning speed correction means that is easier to process and can improve the processing accuracy, instead of an expensive and highly restricted rθ lens or a parabolic mirror that has been proposed in the past. The purpose is to make the system more compact.

Means for Solving the Problems In order to solve the above problems, the light beam scanning optical system according to the present invention includes (a) a light source that generates an intensity-modulated light beam, and (b) scans the light beam at a constant angular velocity. (c) a spherical mirror that folds back the light beam scanned by the deflector and focuses it on the surface of the photoreceptor, and (d) satisfies the following equation.

o, ts<(d/IRMI)<0.45 times, d:
Distance from the point of reflection of the beam toward the center of the scanning area by the deflector to the apex of the spherical mirror (R) Effect of the radius of curvature of the spherical mirror In a configuration that is greater than or equal to the radius of curvature of the spherical mirror, the beam emitted from the light source is scanned at a constant angular velocity by the deflector; The scanning light beam is reflected by a spherical mirror and condensed onto the surface of the photoreceptor. An image can be formed by main scanning by the deflector and sub-scanning by moving the photoreceptor surface. The light flux reflected by the spherical mirror is corrected so that the scanning speed in the main scanning direction is equalized from the center of the scanning area to both ends thereof.

Embodiments Hereinafter, embodiments of the light beam scanning optical system according to the present invention will be described with reference to the accompanying drawings.

In Figure 1, (1) is a semiconductor laser, (5) is a collimator lens, (10) is a polygon mirror, (15) is a beam splitter, (20) is a spherical mirror, and (30) is a drum-shaped photoreceptor. be.

A semiconductor laser (1) emits a diverging light beam that is intensity-modulated by a control circuit (not shown) and carries image information. This diverging light beam is corrected into a substantially parallel light beam by passing through a collimator lens (5). The polygon mirror (10) can be rotated at a constant speed in the direction of arrow (a) about a support shaft (11) by a motor (not shown). Therefore, the parallel light beam that has passed through the collimator lens (5) is reflected by the polygon mirror (1
0) is continuously reflected and scanned at a constant angular velocity.

After this scanning light beam passes through the beam splitter (15), it is reflected on the concave side of the spherical mirror (20), and further,
After being reflected by the beam splitter (15), the photoreceptor (30
). The condensed light flux at this time is the photoreceptor (30
) can be scanned at a constant speed in the axial direction, and this is called main scanning.

Further, the photoreceptor 30) is rotated at a constant speed in the direction of arrow (b), and the scanning by this rotation is called sub-scanning.

That is, in the above light beam scanning optical system, an image (electrostatic latent image) is formed on the photoreceptor (30) by the intensity modulation of the semiconductor laser beam 1) and the main scanning and sub-scanning. As shown in FIG. 2, the spherical mirror (20) is
Instead of the θ lens, the scanning speed in the main scanning direction is corrected so that it becomes equal from the center of the scanning area to both ends thereof.

In detail, as shown in Figure 2, the polygon mirror (10)
from the point (hereinafter referred to as the deflection point) (10a) to the vertex (20a) of the spherical mirror (20).
Regarding the relationship between the distance (d) to a) and the radius of curvature (RM) of the spherical mirror 20), o, 1s<(a/IRMI)<0.45
It is set so as to satisfy the following formula.

In addition, in Fig. 2, (do) is a spherical mirror (20)
It is the distance from the vertex (20a) to the photoreceptor (30).

The lower limit and upper limit of the above formula 0 are values set as an allowable range based on experience depending on the degree of image distortion on the photoreceptor (30). When the lower limit is exceeded, positive distortion increases as the scanning angle increases, and the image becomes elongated at both ends in the main scanning direction (near the start of scanning and near the end of scanning). Furthermore, when the upper limit is exceeded, negative distortion increases as the scanning angle increases, and the image shrinks at both ends in the main scanning direction.

Here, the experimental example (I>, (I[)) in this example.

The configuration data in (III) is shown. Note that the facing distance of the polygon mirror (10) was 23.5 mm.

The aberrations on the photoreceptor condensing surface in each of the above experimental examples (I), (II), and (II[) are shown in FIGS. 3, 4, and 5, respectively. In each figure, (a) is a graph in which the vertical axis is the scanning angle and the horizontal axis is the degree of curvature.The dotted line shows the curvature of field due to the light beam in the deflection plane, and the solid line shows the image due to the light beam in the plane perpendicular to the deflection plane. Shows surface curvature. In the figure, <b) indicates the scanning angle on the vertical axis.
This is a graph with the horizontal axis representing the degree of distortion.

FIG. 6 shows another embodiment of the light beam scanning optical system according to the present invention.

This embodiment uses the beam splitter (
15), and at the same time the spherical mirror (20)
is appropriately inclined so that the incident light and reflected light do not overlap.

In this embodiment, since the beam splitter (15) is not interposed, the attenuation of the amount of light is reduced.

Note that the light beam scanning optical system according to the present invention is not limited to the above-described embodiments, and can be modified in various ways within the scope of the gist.

For example, as a deflector, the polygon mirror (10) described above may be used.
In addition, various types can be used as long as they can scan the light beam in one plane at a constant angular velocity. Further, as the light source, other than a semiconductor laser, other laser generating means or a point light source may be used.

Effects of the Invention As is clear from the above explanation, according to the present invention, a spherical mirror is interposed in the optical path from the deflector to the photoreceptor surface so as to satisfy the above equation 0, so that the scanning speed in the main scanning direction is reduced. In addition to being able to evenly correct It can be an optical system. Moreover, the optical path is folded back by the spherical mirror itself, making the entire optical system compact. It is also advantageous in terms of processing and precision compared to parabolic mirrors and ellipsoidal mirrors, and can be significantly smaller than conventional concave reflecting mirrors.

[Brief explanation of the drawing]

1 to 5 show an embodiment of the present invention, FIG. 1 is a perspective view showing a schematic configuration, FIG. 2 is a diagram schematically explaining an optical path, and FIGS. 3 and 4. , FIG. 5 is a graph showing image distortion at the light condensing surface. FIG. 6 is a perspective view showing a schematic configuration of another embodiment of the present invention. (1)...Semiconductor laser, (5)...Collimator lens, (10)...Polygon mirror, (20)...
Spherical mirror, (30)...photoreceptor.

Claims (1)

[Scope of Claims] 1. A light source that generates an intensity-modulated light beam, a deflector that scans the light beam at a constant angular velocity, and a spherical surface that turns back the light beam scanned by the deflector and focuses it on the photoreceptor surface. mirror, 0.15<(d/|R
_M|)<0.45 times d: distance from the point of reflection of the light beam toward the center of the scanning area by the deflector to the apex of the spherical mirror R_M: satisfies the following formula: radius of curvature of the spherical mirror or more Light beam scanning optical system.