JP2730443B2 - Light beam scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning apparatus used in an image forming apparatus such as a copying machine, a facsimile, and a laser beam printer for forming an image by an electrophotographic system.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. Sho 62-30214 discloses a light beam scanning apparatus in an electrophotographic system. In this light beam scanning device, the incident light path to the polygon mirror and the reflected light path from the polygon mirror are arranged at an angle when viewed from the side in order to reduce the planar size of the entire device. Are arranged so as not to interfere with the optical path or optical system on the reflection side. Further, in order to simplify the unequal velocity on the optical system as much as possible, a light beam is made incident on the polygon mirror from the front of the center of the scanning area. Further, in order to suppress the overall size, in the incident optical system in which the light beam is incident on the deflection means at a certain angle, the light beam from the light source is refracted by the lens member and is incident.

[0003]

However, in the above configuration, in order to refract the light beam and satisfy the above-mentioned incident condition, it is necessary to pass the light beam through the outer portion of the lens having a large aperture. However, even if only a necessary part of the lens is cut out and used, there is a problem that a great deal of labor is required for processing the lens, resulting in high cost.

In addition, the change of the optical path by the lens in the incident optical system largely depends on the processing accuracy of the lens itself, and there are factors that vary such as the position of incidence on the polygon mirror. There is a problem that the refractive index of the lens also changes due to the change in the optical path, and the optical path fluctuates.

The present invention solves the conventional problems without increasing the size of the optical system by forming the lens member constituting the incident optical system into a single lens and directly entering the light beam at a predetermined angle into the deflecting means. It is an object of the present invention to provide a light beam scanning device capable of performing the above.

[0006]

To achieve this object, a light beam scanning apparatus according to the present invention comprises a light source for emitting a flat light beam, a first imaging optical system for shaping and converging the light beam, and a light source. A light beam scanning device comprising: a deflecting unit that reflects and deflects and scans a light beam from the light source, and a second imaging optical system that forms an image of the deflected light beam on the deflection scanning surface on the photosensitive drum surface. The first imaging optical system is constituted by a single lens, and the incident optical axis direction is incident on the deflecting means at a predetermined angle with respect to the scanning plane, and the optical axis direction of the second imaging optical system is viewed from the scanning plane. And a configuration that overlaps with

[0007]

With this structure, the light beam from the light source passes through the optical axis of the single lens and enters the reflecting surface of the deflecting means so that the optical axis of the light beam can be formed without changing the optical path to the reflection point of the deflecting means. Thus, a sufficient range of the lens surface from the deflecting means can be obtained without increasing the size of the first imaging optical system. Further, by making the optical axis of the second imaging optical system on the scanning plane coincide with the incident optical axis of the first imaging optical system as viewed from the scanning plane, the optical system of this scanning device is aligned with the incident optical axis. And symmetric.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

In FIGS. 1 and 2, reference numeral 1 denotes a main body frame which is formed of a high-precision resin molded product. A polygon mirror 2 serving as a deflecting means is arranged at an end of the main body frame 1 and is attached with high precision in a direction perpendicular to a rotation shaft 4 of a drive motor 3 which rotates at high speed.

The reflecting surface of the polygon mirror 2 has a cylindrical shape along the rotating direction, and has a lens effect with the reflecting surface.

A single lens 5 serving as a first imaging optical system is held and fixed by a lens holding member 6 near the center of the main body frame 1, and a semiconductor laser 7 serving as a light source is provided on an end surface of the lens holding member 6. The laser holding member 8 is press-fitted, and an aperture 9 having an elongated slit 10 for controlling the opening of the light emitted from the single lens 5 is mounted on the other end surface. The semiconductor laser 7 emits divergent light having an elliptical cross section, and the beam is shaped and converged by the single lens 5.

FIG. 3 shows the shape of the single lens 5, where the rotation direction of the polygon mirror 2 is the main scanning direction and the direction perpendicular to the main scanning direction is the sub-scanning direction.

In FIG. 3, both the first surface 11 and the second surface 12 of the single lens 5 have an anamorphic shape having different radii of curvature in the main scanning direction and the sub-scanning direction. The minor axis direction is adjusted to the optical axis of the single lens 5 in the sub-scanning direction. The slit of the aperture 9 is also fixed so that its longitudinal direction is aligned with the main scanning direction, and the output optical axis of the single lens 5 is incident on the surface of the polygon mirror 2 at an incident angle A and is directed toward the center of the motor rotation shaft 4. The lens holding member 6 is positioned as described above. Here, since the single lens 5 has a complicated shape, it is formed by directly molding a glass material.

At the other end of the body frame 1, a long single lens 13 which is a second imaging optical system and has a linearity correcting function is perpendicular to the optical axis 14 of the first imaging optical system. , And on the scanning plane of the polygon mirror 2.

In FIG. 2, the single lens 13 has a toric shape in which the first surface side 15 has a negative radius of curvature in the main scanning direction, while the positive radius of curvature changes in the sub-scanning direction from the lens center. The second surface 16 has a cylindrical shape having a positive radius of curvature in the main scanning direction. The single lens 13 also has a complicated shape and a long shape, and is mainly constituted by a high-precision resin molded product having heat resistance and water absorption.

The light beam reflected and deflected from the polygon mirror 2 scans the scanning area B at a reflection angle A and enters the center of the long toric lens 13 in the sub-scanning direction.

Between the long toric lens 13 and the polygon mirror 2, a reflection mirror 17 for changing the optical path is arranged.

In addition to the scanning area B, a beam detection sensor 19 and a beam detection lens 20 composed of a cylinder lens are provided to synchronize the start of image writing.

Further, a photosensitive drum 18 having a rotation axis in the main scanning direction is disposed below the main body frame 1, and is exposed to a latent image by an electrophotographic developing device (not shown).

The operation of the light beam scanning device configured as described above will be described. First, a video signal is sent to the semiconductor laser 7 according to an image signal from the system main body at a fixed clock, and the semiconductor laser 7 is turned on based on a synchronization detection signal from the beam detection sensor 19. The light emitted from the semiconductor laser 7 passes through the single lens 5 and is narrowed down slightly in the main scanning direction, and is narrowed down to a photosensitive drum 18 with a predetermined beam diameter by the cylindrical polygon mirror 2.
On the other hand, in the sub-scanning direction, the light beam once squeezed on the polygon mirror 2 is further squeezed onto the photosensitive drum 18 by the long toric lens 13. Therefore, the ratio of the focal length of the lens in the main scanning direction and the focal length of the lens in the sub-scanning direction is large, and the aperture 9 is large.
Also has a large aperture ratio.

Therefore, it is necessary to make the shape of the emitted beam from the single lens 5 flatter than the elliptical beam from the semiconductor laser 7.

Here, the light beam incident on the polygon mirror 2 at an angle A is reflected at the same reflection angle.
When the polygon mirror 2 is rotated, the mirror surface moves in the front-rear direction, and accordingly, the reflection point of the light beam on the polygon mirror 2 moves up and down to be curved on the scanning surface on the photosensitive drum 18. Therefore, it is desirable that the incident angle A is small, but as the incident angle A becomes smaller, interference between the first imaging optical system and the second imaging optical system occurs, and the beam may be kicked. For this reason, it is necessary to keep the distance between the polygon mirror 2 and the lens of the first imaging optical system to such an extent that interference does not occur, and there is a problem in increasing the size of the lens system.

In this embodiment, by replacing the first image forming optical system with the single lens 5, the incident angle A can be set small without increasing the distance between the polygon mirror 2 and the light source, and the required image forming characteristics are obtained. be able to.

In this embodiment, the curvature radius R and the inscribed radius r of the polygon mirror 2, the polygon mirror 2 and the single lens 5
Distance L, polygon mirror 2 and long toric lens 1
3 distance F, photosensitive drum 18 and long toric lens 1
The distance D between three, the incident angle A, the scanning angle B, the first surface side radius of curvature S1 and the second surface side radius of curvature S of the single lens 5 in the sub-scanning direction.
By setting each of the two to the following dimensions, the scanning curvature on the photosensitive drum 18 can be reduced to 0.2 mm or less.

R = 140 mm, r = 25 mm, L = 70 mm,
F = 152 mm, D = 83 mm, A = 2.5 degrees, B = 30
Degree, S1 = 3 mm, S2 = 130 mm Also, since the light emitted from the single lens 5 passes through the optical axis and directly enters the polygon mirror 2, the polygon mirror 2
There is an excellent effect that has little influence on the position fluctuation on the surface. Accordingly, the imaging characteristics are improved, and it is possible to cope with higher resolution. Further, since this optical configuration is symmetric with respect to the optical axis, it is easy to manufacture a lens,
Since glass is formed by glass molding, the number of parts is greatly reduced, which is advantageous in terms of cost and reliability.

[0026]

As described above, the present invention provides a light source that emits a flat light beam, a first imaging optical system that shapes and converges the light beam, and a deflecting device that reflects and scans the light beam from the light source. Means, and a second imaging optical system for forming an image of the deflected light beam on the deflection scanning surface on a photosensitive drum surface, wherein the first imaging optical system is a single imaging optical system. The polygon mirror 2 has a configuration in which the direction of the incident optical axis is incident on the deflection means at a predetermined angle with respect to the deflection scanning plane and overlaps the optical axis direction of the second imaging optical system when viewed from the deflection scanning plane. A light beam scanning device which can set the incident angle small without increasing the distance between the light beam and the light source and has an excellent effect on the imaging characteristics can be realized.

Further, since the light emitted from the single lens 5 is directly incident on the polygon mirror 2 after passing through the optical axis, there is an excellent effect that there is little influence on the position fluctuation on the polygon mirror 2 surface. . Further, since this optical system is a symmetrical system and the single lens 5 is formed by glass molding, the number of parts is greatly reduced, which is advantageous in terms of cost and reliability.

[Brief description of the drawings]

FIG. 1 is a perspective view of a light beam scanning device according to an embodiment of the present invention.

FIG. 2 is an optical system of a light beam scanning device according to an embodiment of the present invention.

3A is a sectional view of a first imaging optical system in a main scanning direction according to an embodiment of the present invention. FIG. 3B is a sectional view of a first imaging optical system in a sub-scanning direction according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main body frame 2 Polygon mirror 5 Single lens 6 Lens holding member 7 Semiconductor laser 9 Aperture 13 Long toric lens 17 Folding mirror 18 Photosensitive drum

Claims (1)

(57) [Claims] A light source for emitting a flat light beam; a first imaging optical system for shaping and converging the light beam; a deflecting means for reflecting and deflecting and scanning the light beam from the light source; A second imaging optical system for forming an image of the deflected light beam on the photosensitive drum surface, wherein the first imaging optical system comprises a single lens and is incident on the deflecting means. A light beam scanning apparatus, wherein the optical axis direction is incident at a predetermined angle with respect to the deflection scanning plane and overlaps with the optical axis direction of the second imaging optical system when viewed from the deflection scanning plane.