JPH1123990A - Optical scanner and image forming device using the scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanning lens without causing any curvature of image and capable of correcting aberration by setting a radius of curvature of a cutting shape of a beam scan side cut off along a sub-scan direction of a toric lens in asymmetry according to advancing from a central position in the main scan direction to its both sides. SOLUTION: A plane tilt of a deflection surface of a deflector in the sub-scan direction is corrected by a plane tilt correction lens. As the plane tilt correction lens, the toric lens 60 slightly projectingly curving a beam incident side along the main scan direction is used. The toric lens 60 is set asymmetrically so that the radius of curvature R of a beam incident side of a cut-off section in the sub-scan direction becomes gradually large according to advancing from the central position Rc in the main scan direction to its both sides, and becomes gradually small at a displacement point Rh on the way as shown in a line L1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning apparatus and an image forming apparatus in which an optical scanning lens is interposed on the exit side of a deflector for scanning a modulated beam.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, for example, a laser beam oscillated from a beam oscillator 1 and modulated in accordance with input information is rotated as a linear convergent light parallel to a main scanning direction through a collimator lens 2 or the like. After being incident on a polygon mirror or other deflector 3 and converted into a uniform motion by the fθ lens 4 while being deflected and reflected at a predetermined angle by rotation of the deflector 3,
An optical scanning device that corrects the tilt of the deflecting surface 3a of the deflector 3 in the sub-scanning direction by the tilt correction lens 6 and forms and scans an optical dot pattern corresponding to input information on the generatrix of the recording medium 5 includes: It is already known.

[0003]

In general, a cylindrical lens linearly extending in the main scanning direction is used as the surface tilt correction lens 6, but both ends in the longitudinal direction of the lens using such a cylindrical lens are used. For a beam obliquely incident on the lens, the effective radius of curvature of the lens is reduced and the lens acts as a lens with a short focal length. This causes a problem that an image plane in a direction (hereinafter, referred to as a sub-scanning direction) is curved.

In order to solve such a drawback, the cylindrical lens is formed by using a toric lens which is slightly bent along the longitudinal direction (main scanning direction) so that the incident surface on the fθ lens 4 side is convex. 6, the field curvature in the sub-scanning direction is corrected,
Although it has a slightly wavy shape, it can be made to substantially match the recording surface.

On the other hand, in recent years, attempts have been made to increase the angle of view of the deflector 3, shorten the focal length from the deflecting surface 3a to the generatrix of the recording medium 5, and reduce the size of the entire apparatus. As the focal length decreases, the waveform shape is amplified, as shown by the dashed line in FIG. 4, and the field curvature occurs again.

SUMMARY OF THE INVENTION In view of the drawbacks of the prior art, it is an object of the present invention to provide an optical scanning apparatus and an image forming apparatus using an optical scanning lens which does not cause curvature of field and can correct aberration. And Another object of the present invention is that when applied as a surface tilt correction lens, the field angle of the deflector 3 is widened, the focal length is shortened, but the field curvature does not occur, and fθ An object of the present invention is to provide an optical scanning device and an image forming apparatus using an optical scanning lens that can correct aberration when applied as a lens.

[0007]

According to the present invention, in order to achieve the above technical object, the surface tilt correcting lens 6 and the fθ lens 4 interposed between the deflector 3 and the recording medium 5 extend along the sub-scanning direction. Optical scanning device and optical scanning device having an optical scanning lens that has an essential component that the radius of curvature of the cut shape on the beam scanning side that has been cut off is set to be asymmetrical as it goes to both sides from the center position in the main scanning direction. A forming device is proposed.

That is, in an optical scanning device in which a toric lens is interposed on the exit side of a deflector that scans a modulated beam, the toric lens is curved on the beam incident side along the main scanning direction. Provided is an optical scanning device, wherein a radius of curvature of a cut shape on a beam scanning side of the toric lens cut along a sub-scanning direction is set to be asymmetrical as it goes to both sides from a central position in a main scanning direction. I do.

In an image forming apparatus having an optical scanning lens interposed between recording media from an exit side of a deflector that scans a modulated beam, the optical scanning lens is
The beam incident side is formed by a toric lens curved in the main scanning direction, and the radius of curvature of the beam scanning side cut along the sub-scanning direction of the optical scanning lens is in the main scanning direction. There is provided an image forming apparatus characterized in that the image forming apparatus is set asymmetrically as it goes to both sides from the center position.

In these, the “beam scanning side” is
This is a concept including the entrance side or the exit side of the optical scanning lens. As the optical scanning lens, a toric lens such as a cylindrical lens or a toroidal lens, which is generally formed of a plastic lens and has a beam incident side convexly curved along the main scanning direction, is applied.

According to the present invention, since the radius of curvature of the optical scanning lens is set to be asymmetrical as it goes to both sides from the center position in the main scanning direction, a toric which is merely curved as in the prior art is used. The occurrence of field curvature in the recording medium is improved as compared with the lens.

By applying such a sectional structure of the lens to the above-mentioned toric lens, the toric lens itself also has the function of correcting the field curvature and the correction of aberration. Can be achieved. In addition, since the optical scanning lens is configured as a toric lens as described above, it can be molded using a plastic molding die, and is suitable for mass production and practical.

[0013]

Embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the invention, but are merely described. It is only an example.

First, the specific configuration of the optical scanning device having the surface tilt correction lens 6 will be described with reference to FIG.
A polygon mirror having a circumscribed circle having a diameter of 40 mm and a deflecting surface 3a having a hexahedral shape is used, and its reflection width is appropriately selected so that the angle of view incident on the fθ lens is set to approximately 80 °. I have. Lens 2 uses a two-lens lens system composed of a combination of a concave lens and a convex lens.

As shown by the dashed line in FIG. 2, the surface tilt correction lens 6 has the beam incident side slightly curved (for example, a radius of curvature R of about 740 mm) along the main scanning direction.
Its thickness is about 6 mm, and its length in the main scanning direction is about 210
Using a toric lens 60 set to a mm, the radius of curvature R on the beam incident side of the cut section in the sub-scanning direction is set such that the radius of curvature R is larger than the center position Rc in the main scanning direction as shown by the line L1 in FIG. It is set so that it gradually increases as it proceeds to both sides, and gradually decreases at the transition point Rh on the way.

The radius of curvature R on the beam incident side of the cross section in the sub-scanning direction is asymmetric as the radius of curvature R advances to both sides from the center position Rc of the lens as shown by the line L1 in FIG. Is set to The reason is that, with the rotation of the deflecting surface 3a, the reflection point of the deflecting surface 3a also changes, but the trajectory of the change becomes asymmetric about the optical path passing through the central position Rc from the reflection point, This is because field curvature in the sub-scanning direction that occurs on the recording medium 5 also occurs asymmetrically with respect to the optical path.

[0017]

In this embodiment, for example, the radius of curvature R at the center position Rc is set to 15.9 mm, and the radius of curvature R at the transition point Rh at a position approximately 70 mm away from the center position Rc is set to 16.2 mm. . The distance from the deflection surface 3a to the generatrix of the recording medium 5 is set to about 220 mm, and the beam diameter on the optical axis on the generatrix is about 100 μm.

In this embodiment, when the same toric lens 61 having the same radius of curvature R as the above was used as a comparative example, the degree of image curvature in the sub-scanning direction on the generatrix of the recording medium 5 was examined. In FIG. 3, as shown by the one-dot chain line in FIG. 3, the waveform is slightly wavy, but the error is within a maximum of approximately 5 μm, and can be made to substantially match the recording surface.

On the other hand, in the comparative example, as shown by the one-dot chain line in FIG. 4, the waveform becomes large, and the beam diameter changes by about 20 to 30%.

From these data, it is understood that in the present embodiment, the data is accurately matched with the recording surface.

In the present embodiment, the toric lens 60 as described above is applied to the surface tilt correction lens 6, but can also be applied to an fθ lens. That is, at present, the lens is composed of a combination of a plurality of lenses in order to minimize the aberration error of the fθ lens. However, since the toric lens 60 also has an effect on the aberration error in the sub-scanning direction, By applying as a lens, an fθ lens can be configured with a single or a small number of lenses,
The number of parts can be reduced and manufacturing can be facilitated.

Further, in the present embodiment, the occurrence of the field curvature in the recording medium is improved as compared with the conventional toric lens which is merely curved. Further, as the optical scanning lens, a toric lens such as a cylindrical lens or a toroidal lens, which is generally formed of a plastic lens and has a beam incident side convexly curved along the main scanning direction, can be applied. Since the optical scanning lens (toric lens) is configured as described above,
Since it can be molded using a plastic mold, it is practical and suitable for mass production.

[0023]

As described above, according to the present invention, there is provided an optical scanning device and an image scanning apparatus in which the occurrence of field curvature on a recording medium is improved as compared with a conventional optical scanning lens which is merely curved. A forming device can be provided. Also,
It is possible to provide an optical scanning device and an image forming apparatus in which the angle of view of the deflector is widened and the focal length is shortened but the curvature of field does not occur.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a cross-sectional shape of a toric lens according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an optical scanning device to which the present invention is applied.

FIG. 3 is a graph showing the degree of field curvature of a beam diameter according to the embodiment of the present invention.

FIG. 4 is a graph showing the degree of field curvature of a beam diameter in a comparative example.

FIG. 5 is a graph showing the degree of field curvature of a beam diameter in Conventional Example A.

FIG. 6 is a graph showing the degree of field curvature of a beam diameter in Conventional Example B.

[Description of Signs] 3 Deflector 4 fθ lens 5 Recording medium 6 Surface tilt correction lens 60, 61 Toric lens

Claims (2)

[Claims] 1. An optical scanning device comprising a deflector that scans a modulated beam and having a toric lens interposed on an exit side of the deflector, wherein the toric lens has a beam incident side curved along a main scanning direction, and An optical scanning device, wherein a radius of curvature of a cut shape on a beam scanning side of a toric lens cut in a sub-scanning direction is set to be asymmetrical as it goes to both sides from a center position in a main scanning direction. 2. An image forming apparatus comprising an optical scanning lens interposed between a recording medium and an output side of a deflector for scanning a modulated beam, wherein the optical scanning lens is main-scanned on a beam incident side. While forming with a toric lens curved along the direction,
An image forming method, wherein a radius of curvature of a cut shape on a beam scanning side of the optical scanning lens cut along a sub-scanning direction is set to be asymmetrical as it goes from a center position in a main scanning direction to both sides thereof. apparatus.