JPH0658464B2 - Beam optical scanning optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a beam light scanning optical device for scanning a laser beam light by a rotary polygon mirror in, for example, a laser printer.

(Prior Art) Conventionally, as this type of beam light scanning optical device, the one shown in FIG. 2 is known. In FIG. 2, reference numeral 1 is a light source for generating a laser beam light, 2 is a rotary polygon mirror for scanning the laser beam light from the light source 1, and 3 is a laser beam light scanned by the rotary polygon mirror 2 on an image plane 4. It is an image forming lens system for forming an image. That is, the incident laser beam light L incident on the scanning mirror surface S ₁ at a certain point of the rotary polygon mirror 2
₁ is reflected to become a reflected laser beam light L ₂ , which passes through the imaging lens system 3 and is imaged on the imaging surface 4. The reflected laser beam light L ₂ imaged on the image forming surface 4 is diffusely reflected on the image forming surface 4 to become an incident stray light L ₃ , and a part of the incident stray light L ₃ goes backward to pass through the image forming lens system 3. As described above, the light enters the mirror surface S ₂ adjacent to the mirror surface S ₁ and is reflected by the mirror surface S ₂ to become reflected stray light L ₄ , and again passes through the imaging lens system 3 to form the imaging surface 4
Is imaged as unnecessary stray light at a position different from the above.

Here, θ ₄ = θ ₃ + θ ₁ + θ ₂ , and in this case θ ₁
+ Θ ₂ becomes constant. Further, since θ ₃ is an angle fixed by the number of faces of the rotary polygon mirror 2, this is also constant. Further, this type of beam light scanning optical device is fθ
Since an image forming lens system having characteristics is used, if the angle θ ₄ of the reflected stray light L ₄ reflected by the mirror surface S ₂ is constant, the image forming position becomes a certain fixed point P. This appears between the regions where the laser beam is scanned, and is a point that appears in the image.

As means for removing such unwanted stray light, conventionally, a laser beam incident on the rotary polygon mirror 2 L ₁ is tilted by a small amount with respect to the optical axis O of the imaging lens system 3 and is scanned with stray light. After separating the light beam from the light beam, only the stray light is blocked by the light shielding plate 5 provided near the image plane 4.

However, in such a conventional means, since the optical axis O is different from the axis through which the actually scanned laser beam light passes, various aberrations are deteriorated, the correction rate is deteriorated, and the change rate of the beam diameter is large. There was a drawback that

(Problems to be Solved by the Invention) As described above, the conventional stray light removing means has the drawbacks that the aberration is deteriorated, the correction rate is deteriorated, and the beam diameter change rate is increased.

Therefore, the present invention eliminates the above drawbacks, and provides a beam light scanning optical device capable of removing stray light without deteriorating aberrations and the correction rate and the rate of change in beam diameter. With the goal.

[Configuration of the Invention] (Means for Solving the Problems) A beam light scanning optical device of the present invention is a rotary polygon mirror that scans a beam light from a light source and a first surface of the rotary polygon mirror. Of the beam light, a beam light having a predetermined effective scanning area width is formed on the image forming surface, and an image forming optical system is provided with its optical axis aligned with the axis of the beam light.
It is provided at a position between the rotary polygon mirror and the imaging optical system, close to the second surface adjacent to the first surface, and at a position where the boundary of the predetermined effective scanning area is not blocked, and the imaging is performed. A first light blocking member for blocking reflected light from the surface from entering the second surface, and a direction perpendicular to the scanning surface formed by the beam light scanned on the first surface, from the scanning surface. A second light-shielding member provided apart from the first light-shielding member, and a surface of the first light-shielding member facing the image-forming surface reflects light reflected from the image-forming surface toward the second light-shielding member. It is arranged so as to be inclined.

(Operation) As a result, the optical axis of the imaging optical system and the axis through which the beam light actually scanned passes can be made the same, so that the correction rate and the change rate of the beam diameter are not deteriorated without deteriorating the aberration. Stray light can be removed, and image formation due to unnecessary stray light on the image plane can be eliminated.

(Example) Hereinafter, one example of the present invention will be described with reference to the drawings. The same parts as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted. Only different parts will be described in detail. In FIG. 1, a light shielding member 6 is provided between the rotary polygon mirror 2 and the imaging lens system 3 in the vicinity of the rotary polygon mirror 2, and is reflected by the image plane 4 to rotate the polygon mirror 2. The incident stray light L ₃ traveling toward the mirror surface S ₂ adjacent to the scanning mirror surface S ₁ is blocked before reaching the mirror surface S ₂ . By blocking the incident stray light L ₃ with this light blocking member 6, all (or a part) of the reflected stray light L ₄ shown in FIG. 2 is removed and stray light to the fixed point P is eliminated (or the image is affected. It can be set to the amount of light that is not given). Note that L ₅ indicates the boundary of the effective scanning area, and the light blocking member 6 is provided at a position that does not block the boundary L ₅ . Further, as shown in FIG. 1B, the surface S ₃ of the light shielding member 6 on the side of the image plane 4 is formed.
Are not parallel to the image plane 4 and thus prevent the light reflected by the surface S ₃ of the light shielding member 6 from reaching the image plane 4 again in the scanning plane.

Further, as shown in FIG. 1 (b), a light blocking member, such as a slit plate 7, for blocking light that has deviated from the scanning surface to some extent is provided between the rotary polygon mirror 2 and the image forming surface 4. Therefore, all (or part) of the reflected light from the light shielding member 6, the reflected light from the image forming surface 4 and other various stray light are cut off. The slit width of the slit plate 7 is made smaller than the width of the rotary polygon mirror 2,
It is possible to block a part (L ₆ , L ₇ in the figure) of the diffused reflection light from the image plane 4.

Further, in this embodiment, the image forming surface 4 is perpendicular to the optical axis O of the image forming lens system 3 in the sub-scanning direction (actually, the image forming surface 4 moves in the arrow direction, but its moving direction). Not.
As a result, the highest intensity of irregular reflection on the image plane 4 becomes the reflected light L ₆ , but since this reflected light L ₆ is cut by the slit plate 7, only weak reflected light is reflected on the rotary polygon mirror 2. Reaches.

It should be noted that, in the above-described embodiment, the case where the laser beam is scanned by the rotary polygon mirror in the laser printer has been described, but the present invention is not limited to this, and another beam light is scanned by the rotary polygon mirror. It can also be applied to a beam light scanning optical device.

[Effects of the Invention] As described in detail above, according to the present invention, a light blocking member that blocks stray light traveling toward a mirror surface adjacent to a mirror surface of a rotating polygon mirror that scans a light beam before reaching the adjacent mirror surface, By providing between the rotary polygon mirror and the imaging optical system, the optical axis of the imaging optical system and the axis through which the beam light actually scanned passes can be made the same, so that the aberration is not deteriorated, It is possible to provide a beam light scanning optical device capable of removing stray light without deteriorating the correction rate and the change rate of the beam diameter, and eliminating the image formation by the unnecessary stray light on the image forming surface.

[Brief description of drawings]

1 (a) is a schematic plan view for explaining an embodiment of the present invention, FIG. 1 (b) is a schematic side view of FIG. 1 (a),
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 polygonal mirror, 3 ... Imaging lens system (imaging optical system), 4 ... Imaging surface, 6 ... Light blocking member, L ₁
…… Incident laser beam light, L ₂ …… Reflected laser beam light, L ₃ …… Incident stray light, L ₄ …… Reflected stray light.

Claims (2)

[Claims] 1. A scanning optical system for forming an image on an image plane by scanning a beam of light from a light source with a rotating polygonal mirror, and a rotating polygonal mirror for scanning the beam of light from a light source. The light beam having a predetermined effective scanning area width is formed on the image forming surface among the light beams scanned by the first surface, and the optical axis is aligned with the axis of the light beam. Provided at a position between the image optical system and the rotating polygon mirror and the image forming optical system, close to the second surface adjacent to the first surface and not blocking the boundary of the predetermined effective scanning area. And a first light-blocking member that blocks reflected light from the image forming surface from entering the second surface, and a direction perpendicular to the scanning surface formed by the beam light scanned on the first surface. , The second provided apart from the scanning surface
And a surface facing the image forming surface of the first light shielding member is inclined so as to reflect light reflected from the image forming surface toward the second light shielding member. A beam light scanning optical device characterized in that 2. The beam light scanning optical device according to claim 1, wherein the beam light from the light source is a laser beam light.