JPS58190919A - Laser beam optical system - Google Patents

Abstract

PURPOSE:To compensate a fall of a rotary mirror, by using a cylindrical mirror lens which uses the plane side of a flat convex cylindrical lens to a reflector. CONSTITUTION:The plane of a flat convex cylindrical lens 6 is used as a reflecting surface, and a beam is made incident obliquely to the optical axis. Thus the optical path is folded by a reflecting surface and the beam focusing in the subscanning direction is performed simultaneously. The reflected light on the surface of the mirror lens 6 does not come back to a rotary polyhedral mirror as shown by dotted lines. This eliminates the generation of a static ghost and the flare. No dust nor toner is stacked since the lens surface is set downward. Then it is possible to use a cylindrical lens of a long para-axial focal distance owing to the fact that the beam is made incident obliquely to the lens 6. When a beam having 30 deg. inclination to the optical axis is made incident to the lens 6, the incident angle of the beam is set at 20.5 deg. to a photoreceptor. As a result, the ghost due to the reflected light scattered from the surface of the photoreceptor can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser beam optical system using a symmetrical mirror lens in an optical system in an optical scanning device, particularly in an optical system having a function of correcting tilting of a rotary bowl or the like.

In optical writing IIt, a laser beam is scanned onto the photoconductor F using an optical deflector such as a rotating polygon mirror or a hologram scanner and an @ chain element of an fθ lens, and the tilting of each surface of the rotating polygon mirror is performed. The hologram scanner is equipped with a correction optical system for correcting the so-called tilted WA surface caused by misalignment of the hologram, eccentric rings, and variations in each deflection element. Figure 1 shows a known optical system of this type. An example is shown in which a rotating polygon mirror is used as the optical deflector, and the light source part is omitted.

As I know, a gas laser or a semiconductor laser is used, but in the case of a gas laser, the light source is emitted and the light is adjusted to f by a modification such as FiAOM.
It is made into an appropriate size using a beam expander or the like.

Further, in the case of a semiconductor laser, the modulated laser light is converted into an illumination beam by a coupling optical system or a Seisugi optical system.

These beams are formed by the first anamorphic optical system into elongated elliptical beams having long axes substantially perpendicular to the axis of rotation on a rotating polygon [1] and then into an encapsulant filter.

The laser beam f deflected by the rotation r of the rotating polygon mirror 1
The light is reflected onto the photoreceptor 5F by the θ lens 2, and the angles w and 0 are reflected.

In the optical system having the above-mentioned surface tilt correction function, the second
As shown in the diagram 911I of light in the so-called sub-scanning direction that is perpendicular to the scanning direction of the laser beam, the second cylindrical lens 4hζ arrangement fl, the cylindrical lens 4 and the fθ lens 2 are ) illumination, photoreceptor 5, and hK are geometrically and optically placed in a military service relationship. Even if the laser light such as a dot occurs due to the WI@ of the uA surface l due to kneading, the strip fα1 on the photoreceptor
i is kept constant, which prevents the occurrence of so-called "bitch irregularities" in scanning lines.

3 in the figure is a solid mirror that refracts the optical path. This is the ninth type in which the laser beam is incident on the photoreceptor 5 from above.

In the above-mentioned optical arrangement, not only does the transmittance decrease due to the accumulation of dust, toner, etc. on the second lens, but also non-uniform deposition occurs.
According to this arrangement Iij, white streaks are generated in the sub-scanning direction in copying and l: due to '@.
The reflected light from the surface of the cylindrical lens 4 and the scattered light from the surface of the photoreceptor 5 are (b) turned around and returned, and are re-reflected to generate a white streak called a stationary ghost on the photoreceptor 5. do.

The present invention attempts to obtain an optical system that does not have the above-mentioned drawbacks by combining the above-mentioned plane mirror 3 and the second cylindrical lens 4 into one cylindrical mirror lens. 3. As shown in Fig. 3, the movable convex cylinder 1) The flat surface of the cull lens 6 is used as a reflective surface, and the beam is incident diagonally along the optical axis, and the optical path is bent by the 1 reflective surface and in the sub-scanning direction. beam focusing at the same time. In this way, the reflected light on the lens surface of the mirror lens 6 is dangerous because it does not return to the rotating polygon mirror as shown by the dotted line, and stationary ghosts and flares do not occur. And since the lens surface turns orange when facing downward,
In addition to the fact that dust and toner will melt when accumulated, since the beam is obliquely incident on the mirror lens 6, it is possible to use a cylindrical lens with a longer paraxial focal length than the conventional example. As shown in Figure 4, the radius of curvature R1 of the first surface
, the beam passes through a lens whose second surface has a radius of curvature R2, the angle of incidence on the first surface, the angle of incidence on the second surface of refraction #1111.1, the angle of refraction is i2.12, and the geometry in the lens When the approximate optical length is A and the refractive index is n, the effective focal length fe is expressed as follows. 8-piece mirror lens R2=-R.

becomes.

Now the U element of the mirror lens 6 in Fig. 3 R1=　R2=　I　O0,459 Radius of curvature of reflective surface = ψ Center thickness of lens=”t.

If the refractive index of the lens is n=1.52, then the paraxial focal length of this mirror lens is f 1()
However, if a beam tilted by 45 degrees to the optical axis is incident on the top of the lens as shown in the figure, the effective focal length gradient f8 becomes 503
It becomes 4.

In addition, the same mirror lens 6 has a 30 mm diameter on the optical axis as shown in FIG.
When the tilted beam is incident on the top of the lens, the effective focal length f is 74.31).

In this case, the angle of incidence of the beam on the photoreceptor is 2α5 and 6h.
% ghosts caused by scattered reflected light from the surface of the photoreceptor are also reduced.

As described above, the present invention includes a mirror for optical path bending and a second shield.
) By replacing the conventional lens with a single mirror lens, it is possible to reduce the number of parts, eliminate ghosts and flares, prevent copy quality from deteriorating due to dust, etc., and improve the radius of curvature of the lens surface. This has the unique effect of reducing the loss of lenses caused by fire.

[Brief explanation of drawings]

FIG. 1 is a perspective view of essential parts of a known example of an optical scanning device. FIG. 2 is an optical path diagram in the sub-scanning direction, and FIG. 3 is a diagram of the scanning device of the present invention. The optical path diagram of the main part of the paddle example, the 4th figure is the light path diagram of the main part of the ike example when the light beam is obliquely incident on the lens, the @5 figure is the optical path diagram of the main part of the pond example I: Rotating polygon-2 : fθ lens 3: Plane mirror 4:
@2 Cylindrical lens 5: Photoconductor 6: Mirror lens @Applicant Ricoh Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] Includes a light deflector such as a rotating polygon mirror, and bends the $2 cylindrical lens and the traveling light beam to place the light deflection surface and the photoreceptor at the Q stop of military service in terms of geometrical optics. In the optical scanning*W that has the ability to correct the tilt of the optical deflector, which performs exposure scanning from above, the IE2 cylindrical lens and the reflection @ for bending the optical path use the mo-face side of the mo-convex cylindrical lens as a reflecting mirror. A laser beam optical system comprising a cylindrical mirror lens.