JPH04177215A - Optical beam scanning device - Google Patents

Abstract

PURPOSE:To eliminate a need of angular correction or the like with an expensive ftheta lens or the like, make an optical system compact, and enable bidirectional or divisional scanning to be undertaken by providing a reflecting mirror having a spirally formed reflection surface in such a way as to be rotatable about the axis of the spiral. CONSTITUTION:A reflecting mirror 4 having a spirally formed mirror surface 5 is rotated about the axis 4a of a spiral. When a fine parallel beam is irradiated along the aforesaid rotational axis 4a, an incidental optical beam is reflected in a lateral direction, and the incidental position of the beam at the spiral mirror surface 5 moves in the axial progress direction of the beam with the rotation of the mirror surface 5. The aforesaid beam is projected to a sensitive body 8 via a lens system or a mirror system, whenever necessary. As a result, optical beam projected positions change one after another. According to this construction, no ftheta is needed, and an optical system becomes simple and can be constituted in a compact way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam scanning device used in laser beam printers, facsimile machines, scanners, and the like.

[Prior Art] As shown in FIG. 5, in a conventional light beam scanning device, a light beam from a light source (1) such as a semiconductor laser is converted into a rotating polygonal M by a collimating lens (2) and a cylindrical lens (3). (Polygon mirror) (4') and is reflected by this reflecting surface (5).

This reflected beam is converged by a toroidal lens (6') and an fθ lens (7), and is irradiated as a spot onto a target area 1, for example, a photosensitive drum (8) of a laser beam printer.

[Problems to be Solved by the Invention] A conventional light beam scanning device has a deflection angle θ, as shown in a beam reflected by a polygon mirror.

In order to scan at a constant speed on the target surface, the angle is corrected using the fθ lens, and the optical path length must also be corrected at the same time, which complicates the optical system and makes it difficult to design the fθ lens. It was difficult to Therefore, there is a problem in that a printer or the like incorporating the scanning device becomes large in size. Moreover, even if the angle and optical path length are corrected using the fθ lens, the correction is not perfect and there remains the problem that distortion remains.

Furthermore, in the prior art, scanning is limited to only one direction;
It was not possible to perform bidirectional scanning or piecewise scanning.

The present invention aims to solve these problems with a simple configuration, does not require angle correction using an expensive f-theta lens, etc., has a compact optical system, and can perform bidirectional scanning or segmental scanning. The object of the present invention is to provide a scanning device capable of performing the following steps.

[Means for Solving the Problems] Therefore, in order to make the optical system of a light beam scanning device compact, the present invention uses a reflecting mirror (
The mirror surface (5) of 4) is formed into a spiral shape, and the axis of the spiral (4)
It is rotatable around a).

Alternatively, in order to scan in both directions, the mirror surface is formed into a spiral shape with a half pitch, and the half pitch is formed into a spiral shape with an opposite pitch, as shown in FIG.

Alternatively, as shown in FIG. 4, the spiral mirror surface is made discontinuous so that one-piece discontinuous scanning can be performed.

[Operation] As shown in FIG. 1, a reflecting mirror (4) having a mirror surface (5) formed in a spiral shape is rotated about a spiral axis (4a). Then, a thin parallel beam of light is made incident parallel to this rotation axis. Then, the incident light beam is reflected laterally as shown in Fig. 2, and the position where the light beam enters the spiral mirror surface changes in the axial direction as the mirror surface (5) rotates. move in the direction. The beam is transmitted to the photoreceptor (8) via a lens system or mirror system as necessary.
). Therefore, the position where the light beam is projected moves one after another. When the incident light beam enters the rear end of the spiral mirror surface and is reflected, the front end of the spiral mirror enters the optical path of the light beam, so a reflected light beam is formed at the same position as the beginning. Therefore, it functions as a scanning device.

Normal vector 4 on spiral reflective surface P and rotation axis A
As a method to make the angle formed by And the second w! J
As shown in b, if the normal vector 4 passes through the point P and is within the plane S, which is parallel to the axis of rotation and perpendicular to the plane S (see Fig. 2 C), ) can be considered.

In the former case (normal product □), there is no particular restriction on the "distance" between the pitch of the helix and the radius of the reflector (distance between the axis of rotation and point P), but in the latter case (normal method, ) , the pitch of the helix and the circumferential height of the reflecting mirror (radius of helix x 2π) must be equal.

In the case of the spiral mirror surface shown in Fig. 3, which is formed with opposite pitches in half-pitch increments, the incident light beam reaches the rear end of the spiral mirror surface (Ml) with the normal pitch as the spiral portion rotates. Since one reflected light beam is reflected by the spiral mirror surface (M2) with an opposite pitch and returns in the opposite direction, scanning by the light beam is performed in both directions.

In addition, by providing the spiral mirror surfaces (Ml-M5) shown in Fig. 4 at intervals, there are sections where the light beam is reflected and sections where it is not reflected, so that scanning is performed piecewise and discontinuously. It will be.

[Example] Next, the present invention will be explained in more detail by way of examples.

In the following examples, He
-Ne laser was used.

Example 1 Spiral mirror surface with a radius of 15.9 degrees and a pitch of Loom (5
) was created. The normal line of the mirror surface was set at 45 degrees with respect to the central axis of the spiral.

Therefore, a light beam incident parallel to the rotation axis of the helix is reflected in a direction 90 degrees to the direction of incidence.

When this reflecting mirror is rotated at 1 to 200 rpm and the above-mentioned light beam is made incident parallel to the rotation axis, it is reflected in a 90 degree direction, and the projection position of the reflected light changes as the spiral mirror rotates. move in the direction.

It was confirmed that scanning was performed over a width of 100 m.

Example 2 A reflecting mirror having a spiral mirror surface formed by combining mutually opposite spirals with a radius of 31.8 degrees and a pitch of 200 mm in half pitches was produced. The normal line of the mirror surface was set at 45 degrees with respect to the central axis of the spiral.

When this reflecting mirror is rotated at 1 to 200 rpm and a light beam is incident parallel to the rotation axis, it is reflected in a 90 degree direction, and the projection position of the reflected light moves in the direction of travel of the light beam as the spiral mirror rotates. However, from the rear end of the spiral, the reflected light returned in the opposite direction, confirming that round-trip scanning was being performed with 100 reports.

[Effects] As mentioned above, the optical system is simple and compact without requiring the conventional f-theta lens, so it is possible to downsize the device into which the scanning device is installed. This has made it possible to miniaturize laser beam printers, etc. It has also made bidirectional scanning and piecewise scanning possible.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the present invention. FIG. 2 is a cross-sectional view of the spiral reflecting mirror, showing the state of reflection of the light beam. 3 and 4 are perspective views showing other embodiments of the present invention. FIG. 5 is a diagram showing a conventional light beam scanning device. 1... Light source 2... Collimating lens 3... Cylindrical lens 4... Rotating mirror body 5... Reflecting mirror surface 6... ...Toroidal lens 7...Fθ lens 8...Photoconductor Fig. 1 Fig. 2 (0) Fig. 2 (C) Fig. 3

Claims (4)

[Claims] (1) A light beam scanning device in which a reflecting mirror having a spiral reflecting surface can be rotated around the axis of the spiral. (2) The light beam scanning device according to claim 1, wherein the angle between the normal line of the spiral reflecting surface and the rotation axis is 45 degrees. (3) A light beam scanning device according to any one of claims 1 to 2, wherein the spiral reflecting surface is a spiral with a half-pitch in opposite directions. (4) A light beam scanning device according to any one of claims 1 to 3, wherein the spiral reflecting surface is discontinuous at predetermined intervals.