JP3192537B2 - Scanning optical 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 scanning optical apparatus, and more particularly to a scanning optical apparatus in which a light beam emitted from a light source means is deflected by a deflecting element so that fθ
The present invention relates to a scanning optical device suitable for a device such as a laser beam printer or a digital copying machine having an electrophotographic process, in which image information is recorded by optically scanning a surface to be scanned through a lens.

[0002]

2. Description of the Related Art Conventionally, a laser beam printer (L)
In a scanning optical device such as BP), a light beam emitted from a light source is modulated in accordance with an image signal. The light-modulated light beam is periodically deflected by an optical deflector made of, for example, a polygon mirror, and focused by an imaging optical system having fθ characteristics into a spot on a photosensitive recording medium surface to perform optical scanning. We are recording.

FIG. 6 is a schematic view of a conventional scanning optical device. In the figure, a divergent light beam emitted from a light source means 1 is converted into a substantially parallel light beam by a collimator lens 2 and
Thus, the light beam is restricted and enters the cylindrical lens 4. Of the parallel light beams incident on the cylindrical lens 4, they are emitted as they are on the main scanning plane. In the sub-scanning plane, the light converges and forms a substantially linear image on the reflecting surface of the optical deflector 5 formed of a polygon mirror.

A light beam reflected and deflected by the reflection surface of the optical deflector 5 and deflected and scanned in the main scanning surface is guided to the surface 8 to be scanned through an imaging optical system 6 having fθ characteristics. Then, the surface to be scanned 8 is scanned by rotating the optical deflector 5 in the direction of the arrow. The sub-scanning plane is a section including the optical axis and orthogonal to the main scanning plane.

[0005]

In general, a scanning optical device is arranged such that a cylindrical lens 4 is moved back and forth in the optical axis direction in an assembling process so that a spot is excellent in a sub-scanning surface over the entire surface to be scanned (hereinafter, referred to as a scanning optical device). Cylinder adjustment). This is based on the idea that the image plane movement in the sub-scanning plane is divided into a translation component and a curved component, and the translation component is corrected by moving the cylindrical lens back and forth in the optical axis direction. By adjusting the direction, it is possible to suppress tolerances related to optical components and mounting positions in the sub-scanning plane.

[0006] However, since there is no such adjustment in the main scanning plane, it is impossible to correct even if the image plane in the main scanning plane moves in parallel. It was necessary to tighten the tolerances of the optical parts and the mounting positions that would be involved. In addition, it is difficult to perform high-quality printing because the spot cannot be satisfactorily adjusted in the main scanning plane over the entire area to be scanned.

[0007]

A scanning optical device according to the present invention converts a light beam emitted from a light source means, deflects the light beam through an aperture, and deflects it by an optical deflector. A scanning optical device that optically scans the surface to be scanned in the main scanning direction by guiding the light to the main scanning direction and rotating the optical deflector. An anamorphic optical system that converts a light beam in one of the two planes into a parallel light beam and converts a light beam in the other surface into a convergent light beam is provided, and a part of the anamorphic optical system, or the light source unit and the light source unit. By making the anamorphic optical system integrally adjustable in the optical axis direction, the image plane movement in the main scanning plane is corrected independently of the image plane movement in the sub-scanning plane.

[0008]

FIG. 1 is a view showing a scanning optical apparatus according to a first embodiment of the present invention.

Referring to FIG. 1, reference numeral 1 denotes a light source means, for example, a semiconductor laser. Reference numeral 21 denotes a condensing lens, which has a different refractive power between the main scanning plane and the sub-scanning plane in this embodiment.
It is composed of two lenses. Reference numeral 3 denotes an aperture, which limits a light flux (light quantity). Reference numeral 4 denotes a cylindrical lens (cylinder) having a predetermined refractive power only in the sub-scanning plane. The main scanning surface refers to a light beam surface formed by a light beam reflected and deflected by the reflecting surface of the optical deflector 5 and scanned over time. The sub-scanning plane is a section including the optical axis and orthogonal to the main scanning plane.

Reference numeral 5 denotes an optical deflector, which is composed of a polygon mirror, and is rotated in the direction of the arrow by driving means such as a motor. Reference numeral 6 denotes an imaging optical system having fθ characteristics (fθ lens)
And one lens having different curvatures in the main scanning plane and the sub-scanning plane. Reference numeral 8 denotes a photosensitive drum which is a surface to be scanned.

The divergent light beam emitted from the semiconductor laser 1 as a light source is converted into a convergent light beam in the main scanning plane and a parallel light beam in the sub-scanning plane by the anamorphic condenser lens 21. The light quantity of this light beam is restricted by the stop 3 and is incident on the cylindrical lens 4. Of these, the light beam in the main scanning plane directly enters the polygon mirror 5 which is an optical deflector, but the light beam in the sub-scanning plane is imaged by the cylindrical lens 4 near the polygon mirror surface. Therefore, the light beam incident on the polygon mirror 5 becomes a line image elongated in the main scanning direction (the direction in which the light beam is deflected and scanned on the surface to be scanned). The light beam incident on the polygon mirror 5, which is an optical deflector, is deflected and scanned by the rotation of the polygon mirror 5 in the direction of the arrow by the motor.

The light beam deflected by the polygon mirror 5 is converted into an image forming lens 6 having fθ characteristics (hereinafter referred to as an fθ lens).
Is incident on. Here, the fθ lens 6 is composed of one lens, and the surface shape of the lens is aspherical. The aspherical shape has, for example, an origin at the intersection of the fθ lens 6 and the optical axis, an X axis in the optical axis direction, a Y axis in the main scanning plane, and an axis perpendicular to the optical axis in the main scanning plane, and in the sub scanning plane. The axis perpendicular to the optical axis is Z
Axis, the generatrix direction corresponding to the main scanning direction is

[0013]

[Outside 1] Here, R is the radius of curvature, and K, B ₄ , B ₆ , B ₈ , and B ₁₀ are aspherical coefficients.

The sagittal direction corresponding to the sub-scanning direction (the direction orthogonal to the main scanning direction including the optical axis) is

[0015]

[Outside 2] Here, r ′ = r (1 + D ₂ Y ² + D ₄ Y ⁴ + D ₆ Y ⁶
+ D ₈ Y ⁸ + D ₁₀ Y ¹⁰ ). The above equation shows that the generatrix direction is an aspherical surface that can be expressed by a function up to the tenth order, and the sagittal direction is a toric surface having a different curvature depending on the value of Y.

The light beam incident on the fθ lens 6 forms an image on the surface 8 to be scanned by the fθ lens 6 and optically scans the surface 8 to be scanned with the light beam.

FIGS. 2A and 2B are enlarged views of the condenser lens 21 of the present embodiment. FIG. 2A shows a main scanning section, and FIG. 2B shows a sub-scanning section. As shown in FIG. 2, a semiconductor laser 1 as a light source and an anamorphic condenser lens 21 in the present embodiment.
Are integrated into the same unit (hereinafter, referred to as a laser unit), and the laser unit 20 is adjustable in the optical axis direction.

By moving the laser unit 20 back and forth in the optical axis direction, the light beam in the main scanning plane moves its light collecting point back and forth, and the image plane in the main scanning plane also moves in parallel. On the other hand, as for the light beam in the sub-scanning plane, the light beam from the laser unit 20 is a parallel light beam.
The image plane does not move even if the adjustment is made by moving 0 back and forth in the optical axis direction.

That is, it is possible to independently correct only the image plane movement in the main scanning plane by adjusting the laser unit 20 back and forth in the optical axis direction. In addition, since the correction of the image plane movement in the sub-scanning plane can be performed by adjusting the front and rear in the optical axis direction of the cylindrical lens 4 as in the related art, the image plane movement in the main scanning plane and the sub-scanning plane in this embodiment. Correction can be performed at the same time, and higher quality printing can be performed.

Table 1 below shows design values of the scanning optical device of the present embodiment, and FIG. 3 shows the relationship between the adjustment amount of the laser unit and the moving amount of the image plane in the main scanning plane. From this figure, as in the present embodiment, the light source and the anamorphic condenser lens are integrated into the same unit, and by adjusting this unit in the optical axis direction, it is possible to correct the image plane movement in the main scanning plane. Understand.

[0021]

[Table 1]

As described above, the scanning optical device according to the present invention comprises a first optical system for converting a light beam emitted from a light source, and a light beam converted by the first optical system in a main scanning plane.
A second optical system that converts a light beam in one of the sub-scanning surfaces, a deflecting element that deflects and scans the light beam emitted from the second optical system, and spots the light beam on a surface to be scanned. In a scanning optical apparatus including a third optical system for forming an image in a plane, the first optical system converts a light beam in one of the main scanning plane and the sub-scanning plane into a parallel light beam and the other in the other plane. Wherein the second optical system is a cylindrical lens having a refractive power only in the parallel light beam of the first optical system. The first optical system is an anamorphic lens that converts a light beam in the main scanning plane into a convergent light beam and converts a light beam in the sub-scanning plane into a parallel light beam.

Next, a second embodiment of the present invention will be described. The second embodiment differs from the first embodiment in that the condensing lens 22 emits a parallel light beam in the main scanning plane and a convergent light beam in the sub-scanning plane with respect to the light beam from the light source. And the cylindrical lens 42
Is provided not in the sub-scanning plane but in the main scanning plane, and the other configuration is the same as that of the first embodiment.

FIG. 4 is a view showing a second embodiment of the scanning optical device of the present invention, and is an enlarged view of a condenser lens 22 portion.
(A) shows a main scanning section, and (B) shows a sub-scanning section.

The divergent light beam emitted from the semiconductor laser 1 is converged by the anamorphic condenser lens 22 so that the light beam in the main scanning plane is a parallel light beam and the light beam in the sub-scanning plane is focused on the reflecting surface of the polygon mirror 5. Is converted to The converted light beam enters the cylindrical lens 42 having a refractive power only in the main scanning plane via the stop 3. Of these, the light beam in the sub-scanning plane is directly incident on the optical deflector, but the light beam in the main scanning plane is converted into a convergent light beam by the cylindrical lens 42 and is incident on the polygon mirror 5 which is an optical deflector.

Here, the cylindrical lens 42 can be adjusted in the optical axis direction. By this adjustment, the light beam in the main scanning plane moves forward and backward, and the image plane in the main scanning plane also moves in parallel. . Further, the semiconductor laser 1 and the anamorphic condenser lens 22 are formed in the same unit, and by adjusting the optical axis direction of this unit 20, it is possible to correct the image plane movement in the sub-scanning plane as in the conventional case. It is.
Since the light beam from the unit 20 in the main scanning plane is a parallel light beam, this adjustment does not affect the image plane in the main scanning plane at all.

As described above, also in the second embodiment, the correction of the image plane movement in the main scanning plane and the sub-scanning plane can be performed independently, and higher quality printing can be performed.

The third embodiment differs from the first embodiment in that the optical system for converting the divergent light from the semiconductor laser 1 as a light source is composed of a spherical lens 23 and a cylindrical lens 24 having a refractive power only in the main scanning plane. The other configuration is the same as that of the first embodiment described above.

FIG. 5 is a view showing a third embodiment of the scanning optical apparatus of the present invention, and is an enlarged view of the spherical lens 23 portion.
(A) shows a main scanning section, and (B) shows a sub-scanning section.

The divergent light beam emitted from the semiconductor laser 1 is converted into a parallel light beam by the spherical lens 23, and only the light beam in the main scanning plane is converted to a convergent light beam by the cylindrical lens 24. Here, the cylindrical lens 24 can be adjusted in the optical axis direction, and by moving the cylindrical lens 24 back and forth in the optical axis direction, it is possible to correct only the movement of the image plane in the main scanning plane. Also, the correction of the image plane movement in the sub-scanning plane can be performed by adjusting the cylindrical lens 4 as in the first embodiment. Therefore, also in this embodiment, the image plane movement in the main scanning plane and the sub-scanning plane is adjusted. Correction can be performed at the same time, and higher quality printing can be performed.

[0031]

As described above, according to the scanning optical apparatus of the present invention, an optical system for converting the light beam emitted from the light source means is provided in one of the main scanning plane and the sub-scanning plane. Anamorphic optical system that converts the light flux of the other plane into a parallel light flux and converts the light flux in the other plane into a convergent light flux, and a part of the anamorphic optical system, or the light source means and the anamorphic optical system are integrally formed. By making adjustments in the optical axis direction, it is possible to correct the image plane movement in the main scanning plane independently of the image plane movement in the sub-scanning plane. Is effective in reducing the tolerance of the image and forming high-quality images.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a scanning optical device according to a first embodiment of the present invention.

FIGS. 2A and 2B are enlarged views of a condenser lens portion according to a first embodiment of the present invention, wherein FIG. 2A is a cross-sectional view in a main scanning plane, and FIG.

FIG. 3 is a diagram illustrating a relationship between an adjustment amount of a laser unit and an image plane movement amount from a design value in a main scanning plane according to the first embodiment of the present invention.

4A and 4B are diagrams illustrating a scanning optical device according to a second embodiment of the present invention, wherein FIG. 4A is a cross-sectional view in a main scanning plane, and FIG. 4B is a cross-sectional view in a sub-scanning plane.

5A and 5B are views showing a scanning optical device according to a third embodiment of the present invention, wherein FIG. 5A is a cross-sectional view in a main scanning plane, and FIG. 5B is a cross-sectional view in a sub-scanning plane.

FIG. 6 is a diagram showing a conventional scanning optical device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 3 Aperture 4 Cylindrical lens 5 Polygon mirror 6 fθ lens 8 Scanned surface 21 Anamorphic condenser lens 22 Anamorphic condenser lens 23 Spherical lens 24 Cylindrical lens 42 Cylindrical lens

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 26/10

Claims (4)

(57) [Claims] 1. A first device for converting a light beam emitted from a light source.
And a second optical system that converts the converted light beam in one of the main scanning plane and the sub-scanning plane, and a light beam emitted from the second optical system. In a scanning optical device including a deflecting element for deflecting and scanning, and a third optical system for forming an image of this light beam in a spot shape on a surface to be scanned, the first optical system may be in a main scanning plane or in a sub-scanning plane. An anamorphic optical system that converts a light beam in one of the surfaces into a parallel light beam and converts a light beam in the other surface into a light beam other than the parallel light beam,
A scanning optical device, wherein the second optical system is a cylindrical lens having a refractive power only in the parallel light beam of the first optical system. 2. The scanning device according to claim 1, wherein the first optical system is an anamorphic lens that converts a light beam in the main scanning plane into a convergent light beam and a light beam in the sub-scanning plane into a parallel light beam. Optical device. 3. The scanning device according to claim 1, wherein the first optical system is an anamorphic lens that converts a light beam in the main scanning plane into a parallel light beam and a light beam in the sub-scanning plane into a convergent light beam. Optical device. 4. The scanning optical apparatus according to claim 1, wherein the light source and the first optical system are configured as the same unit, and the unit is adjustable in an optical axis direction.