JPS62269925A - Light beam scanning optical system - Google Patents

Abstract

PURPOSE:To remove image formation due to unnecessary stray light on an image formation surface by arranging a light shielding member for interrupting stray light directed to an adjacent mirror surface of a rotary polygon mirror to its mirror surface to be scanned by a light beam before the arrival of the stray light at the adjacent mirror surface between the rotary polygon mirror and an image formation optical system. CONSTITUTION:The light shielding member 6 is arranged between the rotary polygon mirror 2 and the image formation lens system 3 adjacently to the polygon mirror 2 to interrupt incident stray light L3 reflected on an image formation surface 4 and directed to a mirror surface S2 adjacent to a scanning mirror surface S1 of the polygon mirror 2 before the arrival at the mirror surface S2. Since the incident stray light L3 is interrupted by the member 6, the whole (or a part) of the reflected stray light can be removed and stray light to a fixing point P can be removed (or reduced to the light quantity exerting no influence upon an image). The member 6 is arranged on a position where the border L5 of an effective scanning area is not interrupted and the surface S3 of the member 6 on the image formation surface 4 side is set up so as not to be parallel with the image formation surface 4. Consequently, the light reflected on the surface S3 of the member 6 is not reached again on the image formation surface 4 within the scanning surface.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Object of the Invention] (Industrial Field of Application) The present invention relates to a beam light scanning optical system in which a laser beam is scanned by a rotating polygon mirror in, for example, a laser printer. Regarding equipment.

(Prior Art) Conventionally, as this type of beam light scanning optical device, the one shown in FIG. 2 is known. In Fig. 2, 1 is a light source that generates a laser beam, 2 is a rotating polygon mirror that scans the laser beam from the light source 1, and 3 is a mirror that combines the laser beams scanned by the rotating polygon mirror 2. This is a convex lens system that forms an image on 4. In other words, the incident laser beam incident on the scanning X^ plane $1 at a certain point in time of the rotating polygon mirror 2 is
is reflected to become a reflected laser beam L2, which passes through the imaging lens system 3 and is imaged on the imaging surface 4.

The reflected laser beam L2 focused on the imaging surface 4 is diffusely reflected on the imaging surface 4 to become incident stray light L3, and a part of this incident stray light L3 goes backwards and passes through the imaging lens system 3 to form the above-mentioned It enters the mirror surface S2 adjacent to the mirror surface S1, is reflected by the mirror surface S2, becomes a foul stray light 4, passes through the imaging lens system 3 again, and is focused on a different position on the imaging surface 4 as unnecessary stray light. imaged.

Here, θ4-03〇l+02, in this case θ1
+θ2 becomes constant. Furthermore, since θ3- is an angle fixed by the number of rotating polygons 1 and 2, it is also constant. Furthermore, since this type of beam light scanning optical device uses an imaging lens system with fθ characteristics, if the angle θ4 of the reflected stray light reflected by the mirror surface S2 is constant, the imaging position will be at a certain This becomes a fixed point P. This occurs between certain areas of laser beam light scanning, and becomes the point that appears in the image.

Conventionally, as a means to remove such unnecessary stray light, a rotating polygon! After tilting the incident laser beam L1 to lt2 by a minute amount with respect to the optical axis O of the imaging lens system 3 and separating the stray light and the scanned laser beam, a light shielding light provided near the imaging surface 4 is used. The plate 5 was designed to block only stray light.

However, with such conventional means, since the optical axis ○ is different from the axis through which the actually scanned laser beam and beam light pass, various aberrations deteriorate, the correction rate worsens, and the rate of change in the beam diameter also decreases. It had the disadvantage of being large.

(Problems to be Solved by the Invention) As described above, the conventional stray light removing means has the drawbacks of degrading aberrations, worsening the correction rate, and increasing the rate of change in beam diameter.

SUMMARY OF THE INVENTION Accordingly, the present invention aims to eliminate the above-mentioned drawbacks, and provides a beam light scanning optical device that can remove stray light without deteriorating aberrations or deteriorating the correction rate or the rate of change in beam diameter. With the goal.

[Structure of the Invention] (Means for Solving the Problems) The beam light scanning optical device of the present invention allows stray light traveling toward a mirror surface adjacent to a mirror surface of a rotating polygon mirror that scans a beam light to reach the adjacent mirror surface. A light-shielding member that blocks light from the light is provided between the rotating polygon mirror and the imaging optical system.

(Function) As a result, the optical axis of the imaging optical system and the axis through which the actually scanned beam light passes can be made the same, so aberrations are not deteriorated and the correction rate and the rate of change in beam diameter are not deteriorated. Stray light can be removed, and image formation due to unnecessary stray light on the imaging plane can be eliminated.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. Note that the same parts as those in FIG. 2 are given the same reference numerals, and the explanation thereof will be omitted, and only the different parts will be explained in detail. In FIG. 1, 6 is a light shielding member, and a rotating polygon 1512
It is provided close to the rotating polygon mirror 2 between the image forming lens system 3 and the imaging lens system 3, and prevents incident stray light L3 from being reflected on the image forming surface 4 and directed toward the mirror surface S2 adjacent to the scanning mirror surface S1 of the rotating polygon mirror 2. , is cut off before reaching the mirror surface S2.

By blocking the incident stray light 3 with this light shielding member 6,
By removing all (or part) of the reflected stray light L4 shown in FIG. 2, it is possible to eliminate stray light from reaching the fixed point P (or to make it a light source that does not affect the image). Note that L5 indicates the boundary of the effective scanning area, and the light shielding member 6 is provided at a position that does not block the boundary L5. Also, the first
As shown in FIG.
The surface $3 of ll is not parallel to the image forming surface 4, thereby preventing the light reflected by the surface S3 of the light shielding member 6 from reaching the image forming surface 4 again within the scanning plane. There is.

Further, as shown in FIG. 1(b), a light blocking member such as a slit plate 7 is provided between the rotating polygon mirror 2 and the imaging surface 4 to block light that deviates from the scanning surface to some extent. It is designed to cut out all (or part) of the reflected light from the light shielding member 6, the reflected light from the imaging surface 4, and various other stray lights. Note that by making the slit width of the slit plate 7 smaller than the width of the rotating polygon mirror 2,
A part of the diffusely reflected light from the imaging surface 4 (6° 17 in the figure) can be blocked.

Furthermore, in this embodiment, the image forming surface 4 is perpendicular to the optical axis O of the focusing lens system 3 in the sub-scanning direction (actually, the image forming surface 4 moves in the direction of the arrow, but in the moving direction). Not.

As a result, the part of the imaging surface 4 where the intensity of diffuse reflection is highest becomes the reflected light L6, but since this reflected light La is cut by the slit plate 7, only the weak reflected light reaches the rotating polygon mirror 2. .

In the above embodiment, a case has been described in which a laser beam is scanned by a rotating polygon mirror in a laser printer, but the present invention is not limited to this, and other beams may be scanned by a rotating polygon mirror. It can also be applied to beam light scanning optical devices.

[Effects of the Invention] As described in detail above, according to the present invention, a light shielding member that blocks stray light directed toward a mirror surface adjacent to a mirror surface of a rotating polygon mirror that scans a beam light before reaching the adjacent mirror surface is provided. By installing it between the rotating polygon mirror and the imaging optical system, the optical axis of the imaging optical system and the axis through which the actually scanned beam light passes can be made the same, so aberrations can be corrected without deteriorating. It is possible to provide a beam light scanning optical device that can remove stray light without deteriorating the rate of change in beam diameter and the rate of change in beam diameter, and can eliminate image formation due to unnecessary stray light on an imaging plane.

[Brief explanation of the drawing]

FIG. 1(a) is a schematic plan view for explaining one embodiment of the present invention, FIG. 1(b) is a schematic side view of FIG. 1(a),
FIG. 2(a) is a schematic plan view for explaining a conventional beam light scanning optical device, and FIG. 2(b) is a schematic side view of FIG. 2(a). 1...Light source, 2...Rotating polygon mirror, 3.
...Imaging lens system (imaging optical system), 4...
・Imaging surface, 6... Light shielding member, Ll...
Incident laser beam light, L2... reflected laser beam light, L3... incident stray light, L4... reflected stray light. Applicant's agent Patent attorney Takehiko Suzue (b) Figure 1 (b) Figure 2

Claims (2)

[Claims] (1) A rotating polygon mirror that scans the beam light from the light source; An imaging optical system that images the beam light scanned by the rotating polygon mirror onto an imaging plane; The rotating polygon mirror and the imaging optical system. a light beam provided between the light beam and a light shielding member that blocks stray light directed toward a mirror surface adjacent to a mirror surface of the rotating polygon mirror that scans the beam light before reaching the adjacent mirror surface; Scanning optics. (2) The beam light scanning optical device according to claim 1, wherein the light beam from the light source is a laser beam light.