JPH07140404A - Scanning optics - Google Patents

Abstract

(57) [Summary] [Purpose] 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, and reduce the tolerance of the precision of optical components and their positional precision. At the same time, a scanning optical device that is effective for high-quality image formation is provided. A first optical system for converting a light beam emitted from a light source, and a second optical system for converting a light beam in the main scanning surface or the sub-scanning surface of the converted light beam. When,
In the scanning optical device including a deflecting element that deflects and scans the light beam emitted from the second optical system, and a third optical system that forms the light beam into a spot on the surface to be scanned, the first optical system. The optical system is an anamorphic optical system that converts a light beam in one of the main scanning surface and the sub-scanning surface into a parallel light beam and converts a light beam in the other surface into a light beam other than the parallel light beam, and the second optical system is It is a cylindrical lens having a refracting power only for the parallel light flux of the first optical system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device, and in particular, a light beam emitted from a light source means is deflected by a deflecting element 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, which records image information by optically scanning a surface to be scanned through a lens.

[0002]

2. Description of the Related Art Laser beam printers (L
In a scanning optical device such as BP), the light flux emitted from the light source means is optically modulated according to the image signal. Then, the light-modulated light beam is periodically deflected by an optical deflector including a polygon mirror, and is focused in a spot shape on a photosensitive recording medium surface by an image forming optical system having an fθ characteristic, and optically scanned to form an image. I am recording.

FIG. 6 is a schematic view of a conventional scanning optical device. In the figure, the divergent light beam emitted from the light source means 1 becomes a substantially parallel light beam by the collimator lens 2, and the diaphragm 3
The light flux is limited by and is made incident on the cylindrical lens 4. Within the main scanning plane, the parallel light flux incident on the cylindrical lens 4 is emitted in the state of the parallel light flux as it is. In the sub-scanning plane, they converge and form a substantially linear image on the reflecting surface of the optical deflector 5 composed of a polygon mirror.

The 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 to be scanned 8 through the imaging optical system 6 having the fθ characteristic. The surface to be scanned 8 is scanned by rotating the optical deflector 5 in the direction of the arrow. The sub-scanning surface is a cross section including the optical axis and orthogonal to the main scanning surface.

[0005]

Generally, in a scanning optical apparatus, the cylindrical lens 4 is moved back and forth in the direction of the optical axis in the assembling process so that a good spot is obtained in the sub-scanning surface over the entire surface to be scanned. Cylinder adjustment). This is based on the idea that the image plane movement in the sub-scanning plane is divided into a parallel movement component and a curved component, and the parallel movement 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 the tolerance associated with the optical components and the mounting position in the sub-scanning plane.

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 is translated, and the movement of the image plane in the main scanning plane is not corrected. It was necessary to tighten the tolerances of the accompanying optical components and mounting positions. Further, it is difficult to perform high-quality printing because the spot cannot be satisfactorily adjusted within the main scanning surface over the entire surface to be scanned.

[0007]

In the scanning optical apparatus of the present invention, a light beam emitted from a light source means is converted and deflected by an optical deflector through a diaphragm, and then on a surface to be scanned through an imaging lens. In the scanning optical device that optically scans the surface to be scanned in the main scanning direction by guiding the light to and rotating the optical deflector, as an optical system for converting the light flux from the light source means, in the main scanning surface and the sub scanning surface. A light flux in either one of the surfaces is a parallel light flux, and an anamorphic optical system for converting the light flux in the other surface into a convergent light flux is provided, and a part of the anamorphic optical system, or the light source means and the The anamorphic optical system is integrally adjustable in the optical axis direction to correct the image plane movement in the main scanning plane independently of the image plane movement in the sub-scanning plane.

[0008]

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

In the figure, reference numeral 1 is a light source means, which is composed of, for example, a semiconductor laser. Reference numeral 21 denotes a condenser lens, which has different refracting powers in the main scanning plane and the sub-scanning plane in this embodiment.
It consists of one lens. A diaphragm 3 limits the luminous flux (light quantity). A cylindrical lens (cylinder) 4 has a predetermined refracting power only in the sub-scanning plane. The main scanning surface refers to a ray bundle surface formed by the light flux scanned by being reflected and deflected by the reflecting surface of the optical deflector 5 with time. The sub-scanning surface is a cross section including the optical axis and orthogonal to the main scanning surface.

An optical deflector 5 is composed of a polygon mirror and is rotated in the direction of the arrow by a driving means such as a motor. 6 is an imaging optical system (fθ lens) having fθ characteristics
The main scanning plane and the sub-scanning plane each have a different curvature. 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 the light source means is converted by the anamorphic condenser lens 21 into a convergent light beam in the main scanning plane and a parallel light beam in the sub-scanning plane. The light amount of this light flux is limited by the diaphragm 3 and enters the cylindrical lens 4. Of these, the light flux in the main scanning plane is directly incident on the polygon mirror 5 which is an optical deflector, while the light flux in the sub-scanning plane is imaged near the polygon mirror surface by the cylindrical lens 4. Therefore, the light beam incident on the polygon mirror 5 becomes a line image that is long in the main scanning direction (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 by the motor in the arrow direction.

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

[0013]

[Outer 1] Where 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 (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 formula 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 the surface 8 to be scanned is optically scanned with the light beam.

2A and 2B are enlarged views of the condenser lens 21 of this embodiment. FIG. 2A shows a main scanning section and FIG. 2B shows a sub scanning section. As shown in FIG. 2, the semiconductor laser 1 and the anamorphic condenser lens 21 which are the light source in this 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 collecting point of the light beam in the main scanning plane moves back and forth, and the image plane in the main scanning plane also moves in parallel. On the other hand, since the light flux from the laser unit 20 is a parallel light flux in the sub-scanning plane, this laser unit 2
The image plane does not move even if 0 is moved back and forth in the optical axis direction for adjustment.

That is, it is possible to independently correct only the image plane movement in the main scanning plane by adjusting the front and rear of the laser unit 20 in the optical axis direction. Further, since the correction of the image plane movement in the sub-scanning plane can be performed by the forward / backward adjustment in the optical axis direction of the cylindrical lens 4 as in the conventional case, the image plane movement in the main scanning plane and the sub-scanning plane is performed in this embodiment. Can be corrected at the same time, and higher quality printing is possible.

Table 1 below shows design values of the scanning optical device of this embodiment, and FIG. 3 is a diagram showing the relationship between the adjustment amount of the laser unit and the image plane movement amount in the main scanning plane. From this figure, it is possible to correct the image plane movement within the main scanning plane by adjusting the light source and the anamorphic condenser lens into one unit by adjusting the unit in the optical axis direction as in this embodiment. Recognize.

[0021]

[Table 1]

As described above, the scanning optical device of the present invention includes the first optical system for converting the light beam emitted from the light source, and the main scanning plane of the light beam converted by the first optical system,
A second optical system that converts a light beam in either one of the sub-scanning planes, a deflection element that deflects and scans the light beam emitted from the second optical system, and a spot of this light beam on the surface to be scanned. In a scanning optical device including a third optical system for forming a uniform image, the first optical system converts a light beam in either the main scanning plane or the sub-scanning plane into a parallel light beam and in the other plane. Is an anamorphic optical system for converting the light flux of the first optical system into a light flux other than the parallel light flux, and the second optical system is a cylindrical lens having a refracting power only for the parallel light flux of the first optical system. The first optical system is an anamorphic lens that converts a light beam in the main scanning surface into a convergent light beam and a light beam in the sub scanning surface 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 condenser lens 22 emits a parallel light beam in the main scanning plane and a convergent light beam in the sub-scanning surface with respect to the light beam from the light source. And the cylindrical lens 42
The refracting power of is applied not only in the sub-scanning surface but also in the main scanning surface, and other configurations are the same as in 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 the 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 an image on the reflecting surface of the polygon mirror 5. Is converted to. The converted light flux enters the cylindrical lens 42 having a refractive power only in the main scanning plane via the diaphragm 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 the optical deflector.

Here, the cylindrical lens 42 can be adjusted in the direction of the optical axis, and by this adjustment, the light collecting point of the luminous flux in the main scanning plane moves back and forth, 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 by 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. Is.
Since the light flux from the main unit 20 in the main scanning plane is a parallel light flux, the image plane in the main scanning plane is not affected by this adjustment.

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 independently performed, 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 the light source has a spherical lens 23 and a cylindrical lens 24 having a refracting power only in the main scanning plane. It is composed of two sheets, and the other structure 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 becomes a parallel light beam by the spherical lens 23, and only the light beam in the main scanning plane becomes a convergent light beam by the cylindrical lens 24. Here, the cylindrical lens 24 is adjustable 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 image plane movement within the main scanning plane. Further, since 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, the image plane movement in the main scanning plane and the sub-scanning plane is also performed in this embodiment. Can be corrected at the same time, and higher quality printing is possible.

[0031]

As described above, according to the scanning optical device of the present invention, as an optical system for converting the light beam emitted from the light source means, either in the main scanning plane or in the sub scanning plane. Of the anamorphic optical system for converting the light flux of the above into a parallel light flux and converting the light flux in the other surface into a convergent light flux, a part of the anamorphic optical system, or the light source means and the anamorphic optical system are integrally formed. By adjusting in the direction of the optical axis, 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. It is effective for forming high-quality images while reducing the tolerance.

[Brief description of drawings]

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

FIG. 2 is an enlarged view of a condenser lens portion of the first embodiment of the present invention, (A) is a cross-sectional view in the main scanning plane, and (B) is a cross-sectional view in the sub-scanning plane.

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

4A and 4B are views showing a scanning optical device according to a second embodiment of the present invention, FIG. 4A being a sectional view in a main scanning plane and FIG. 4B being a 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, FIG. 5A being a sectional view in a main scanning plane and FIG. 5B being a sectional view in a sub-scanning plane.

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

[Explanation of symbols]

 1 Semiconductor Laser 3 Aperture 4 Cylindrical Lens 5 Polygon Mirror 6 fθ Lens 8 Scanned Surface 21 Anamorphic Focusing Lens 22 Anamorphic Focusing Lens 23 Spherical Lens 24 Cylindrical Lens 42 Cylindrical Lens

Claims (4)

[Claims] 1. A first device for converting a light beam emitted from a light source.
Of the optical system, the second optical system for converting the light flux of the converted light flux in either the main scanning plane or the sub-scanning plane, and the light flux 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 includes a main scanning surface and a sub-scanning surface. An anamorphic optical system that converts a light beam in one surface into a parallel light beam and converts a light beam in the other surface into a light beam other than a parallel light beam,
A scanning optical device, wherein the second optical system is a cylindrical lens having a refracting power only for the parallel light flux of the first optical system. 2. The scanning according to claim 1, wherein the first optical system is an anamorphic lens that converts a light beam in the main scanning surface into a convergent light beam and a light beam in the sub-scanning surface into a parallel light beam. Optical device. 3. The scanning 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 device according to claim 1, wherein the light source and the first optical system are configured as a single unit, and the unit is adjustable in the optical axis direction.