JP2629870B2 - Surface tilt correction scanning optical system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface tilt correction scanning optical system mainly used for a laser beam printer or the like and for removing unevenness in pitch of a scanning line in a sub-scanning direction.

More specifically, a linear imaging optical system that linearly images a light beam emitted from a light source on a deflecting and reflecting surface of a deflector, and a light beam reflected and deflected by the deflector on an object to be scanned. More specifically, the present invention relates to the above-described linear imaging optical system including a surface tilt correction scanning optical system including a scanning imaging optical system for forming an image.

[Prior art] In addition to the advantage that a laser beam printer can perform recording at an extremely high speed, recently, miniaturization and cost reduction have been gradually realized, and with the diversification and development of OA equipment, more and more. Its demand is growing.

Next, such a laser beam printer will be described with reference to FIG.

A laser beam B directly modulated in accordance with image information from a semiconductor laser 1 as a light source is converged in a direction orthogonal to a scanning surface by a linear imaging optical system 2, and is deflected and reflected by a polygon mirror 3, which is a deflector. An image is formed linearly on the surface 3a.
The laser beam B reflected by the deflecting / reflecting surface 3a is deflected by the rotation of the polygon mirror 3, and is imaged on the photosensitive drum 5 by an fθ lens 4 which is a scanning image forming system.
It is configured to scan in the direction.

In such a laser beam printer, a deflecting reflecting surface 3a of a deflector such as a polygon mirror 3 used for scanning the light beam B from the light source 1 has a manufacturing error, a mounting error, or a vibration during rotation. There is some tilt error in the direction perpendicular to the scanning plane.

Therefore, in the light beam B reflected by the deflecting reflection surface 3a having such a tilt error, the image forming position on the object to be scanned is shifted in the sub-scanning direction, and the scanning line pitch becomes uneven. The unevenness of the pitch of the scanning lines causes a decrease in the image quality of the recording in a recording apparatus such as a laser beam printer.

The above-described surface tilt correction scanning optical system is for eliminating such pitch unevenness of the scanning line, and the light beam B from the light source 1 is temporarily shifted by the linear imaging optical system 2 in a direction orthogonal to the scanning surface. The beam is converged to form a linear image on the deflecting / reflecting surface 3a of the deflector, and the light beam from the deflecting / reflecting point is restored in this direction by the scanning imaging optical system to form a conjugate image on the scanned object. This is to avoid the influence of the tilt error of the deflecting reflection surface 3a.

In this specification, the “scanning surface” is a plane formed by a time-series set of light beams to be scanned,
In other words, it means a plane including the main scanning line on the object to be scanned and the optical axis of the surface tilt correction scanning optical system.

[Problems to be Solved by the Invention] Conventionally, a linear imaging optical system for a light source having a large divergence angle, such as a semiconductor laser, in such a scanning optical system,
The light beam emitted from the light source is first converted into a light beam substantially parallel to the collimator lens, and then a linear image is formed on the deflection / reflection surface by a cylindrical lens having a positive refractive power in a direction perpendicular to the scanning surface. there were.

In this case, although it differs depending on the size of the divergence angle of the light source and the ratio of the light beam taken in by the collimator lens, a collimator lens usually requires a lens system of 2 to 4 elements, and furthermore, a cylindrical lens is arranged. This forms a linear imaging optical system.

An object of the present invention is to provide a surface tilt correction optical system which aims to greatly reduce the cost in which the linear imaging optical system is constituted only by the simplest single lens and to further simplify the adjustment extremely.

[Means and Actions for Solving the Problems] In the linear imaging optical system of the surface tilt correction scanning optical system according to the present invention, the light source side has a convex surface in a direction orthogonal to the scanning surface, and the deflector side has an optical axis symmetric convex surface. It is characterized by comprising a single lens.

In the linear imaging optical system according to the present invention, the light beam emitted from the light source is formed such that the surface on the light source side is convex in a direction orthogonal to the scanning direction, and the surface on the deflector side is a convex surface having optical axis symmetry. In the scanning plane direction, the light flux is substantially parallel, and in a direction orthogonal to the scanning plane direction, a linear image is formed on the deflector.

When the divergence angle of the light source is large and a large amount of light emitted from the light source is taken in, it is desirable to make the surface on the deflector side a convex aspheric surface having optical axis symmetry to reduce aberration.

Further, it is desirable that the surface on the light source side be an aspheric surface that is convex in a direction orthogonal to the scanning direction, and that aberration correction in this direction be further improved.

NA ^* in the direction perpendicular to the scanning plane of the light beam that forms a linear image on the deflector surface is the divergence angle of the light source in this direction, the ratio of the light beam taken in, the final spot diameter on the object to be scanned, and the scanning optical system. It is determined by the magnification in the direction perpendicular to the scanning plane (that is, in this direction, the deflection point and the object to be scanned are in a substantially conjugate relationship and indicate the imaging magnification in order to correct surface tilt).
When this NA ^* is large, it is necessary to reduce the aberration in this direction by making the surface on the light source side an aspheric surface convex in a direction perpendicular to the scanning direction.

That is, in the direction orthogonal to the scanning direction, a larger NA is obtained by determining the convex aspheric surface (direction orthogonal to the direction) on the light source side according to the convex aspheric surface (optical axis symmetry) on the deflector side.
^{For *} , the above linear imaging system is obtained.

In this way, since the linear imaging optical system can be configured with only a single lens, it is possible to greatly reduce the cost and simplify the adjustment.

In particular, in cost reduction, for example, according to a manufacturing method such as direct pressing of a lens, the effect is very large.

Embodiment An embodiment of the present invention will be specifically described below with reference to the drawings. The surface tilt correction scanning optical system according to the present invention is an optical system used in a laser scanning device such as a laser beam printer.

As shown in FIG. 7, the laser scanning device includes a semiconductor laser as a light source, a linear imaging optical system 2, a polygon mirror 3,
It is composed of an fθ lens 4, a photosensitive drum 5, and the like.

The semiconductor laser 1 emits a laser beam B directly modulated in accordance with screen information, and this laser beam B, which is an example of a light beam, is converged linearly by a linear imaging optical system 2 and deflected by a deflector. An image is formed on the deflection reflection surface 3a of the polygon mirror 3 as an example. The laser beam B reflected by the deflecting / reflecting surface 3a is deflected by the rotation of the polygon mirror 3, and is imaged on the photosensitive drum 5 by an fθ lens 4 which is an example of a scanning image forming optical system. Scanning is performed in the direction A in the figure.

The surface tilt correction scanning optical system mainly includes the above-described linear imaging optical system 2 and the scanning imaging optical system 4, and is used to reduce the deviation of the scanning line pitch caused by the surface tilt of the deflecting reflection surface 3a of the deflector 3. It is to be removed.

Tables 2 and 3 show the specifications of Examples 1 and 2 showing the specific configuration of the linear imaging optical system 2 according to the present invention.

Note that there are two examples, and FIG. 1 and FIG. 2 respectively show lens configuration diagrams, and FIG. 3 to FIG. 6 show aberration curve diagrams. Table 1 below shows the correspondence between them.

In each lens configuration diagram, (A) shows the lens arrangement cut along the scanning plane, and (B) shows the lens arrangement cut along a plane perpendicular to the scanning plane.

The aberration curves in each aberration diagram are traced in the direction opposite to the actual traveling direction of the light beam and evaluated on the light source surface.

That is, in both of the first and second embodiments, the light beam emitted from the light source becomes a parallel light beam in the direction along the scanning plane after passing through the optical system, and forms an image in the direction perpendicular to the scanning plane.

[Effects of the Invention] As described above, according to the present invention, a linear imaging optical system of a surface tilt correction scanning optical system can be configured with only the simplest single lens. In addition, it is possible to form an extremely clear scanning optical system without deteriorating any performance.

[Brief description of the drawings]

The drawings show an embodiment of a surface tilt correction scanning optical system according to the present invention, and FIGS. 1 (A) and (B) and FIGS. 2 (A) and (B).
FIG. 1A is a lens configuration diagram of an embodiment, and FIG.
FIG. 1A is a lens configuration diagram cut in a direction along the scanning surface, FIGS. 1B and 2B are lens configuration diagrams cut in a direction orthogonal to the scanning surface, FIGS. 4 is an aberration diagram in a direction along a scanning surface in each embodiment. FIGS. 5 and 6 are aberration diagrams in a direction along a scanning surface in each embodiment. FIG. 7 is scanning by a laser beam printer. It is the schematic of an apparatus. DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Linear imaging optical system 3 ... Deflector 3a ... Deflection reflection surface 4 ... Scanning imaging optical system 5 ... Scanned object B ... Light beam

Claims (2)

(57) [Claims] 1. A linear imaging optical system for linearly imaging a light beam emitted from a light source on a deflecting and reflecting surface of a deflector, and a light beam reflected and deflected by the deflector on an object to be scanned. A scanning image forming optical system for forming an image, wherein the linear image forming optical system is configured such that the light source side is a convex surface in a direction orthogonal to the scanning surface, and the deflector side is an optical axis symmetric. A surface tilt correction scanning optical system comprising a single lens having a convex surface. 2. A linear imaging optical system comprising a single lens having a convex aspheric surface on a light source side in a direction orthogonal to a scanning surface and a convex aspheric surface on a deflector side in an optical axis. The scanning optical system according to claim 1, wherein