JPS6350814A - Surface tilt correcting and scanning optical system - Google Patents

Abstract

PURPOSE:To increase an angle of field in a main scanning direction while maintaining image formation characteristics and a surface tilt correcting function excellently by arranging the 1st lens with a specific cylindrical surface and the 2nd lens with a toric surface. CONSTITUTION:The scanning image formation optical system 3 which forms the image of light beam flux B reflected and deflected by a deflector 4 on a body 6 to be scanned consists of the 1st lens G1 which has the 1st cylindrical surface having its axis at right angles to the scanning surface and the 2nd cylindrical surface having its axis crossing the optical axis in the scanning surface at right angles, and the 2nd lens G2 which has a toric surface in order from the side of the deflector 4. Namely, the cylindrical surfaces and toric surface are provided to the different lenses G1 and G2. Consequently, the image formation characteristics at right angles to the scanning surface are maintained excellently over a considerably wide range and the degree of freedom of design along the scanning surface increases.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface tilt correction scanning optical system that is mainly used in laser beam printers and the like and eliminates pinch unevenness in the sub-scanning direction of scanning lines.

More specifically, it includes a linear imaging optical system that forms a linear image of a beam of light emitted from a light source onto a deflection/reflection surface of a deflector, and a linear imaging optical system that forms a linear image of a beam of light emitted from a light source onto a deflection/reflection surface of a deflector, and a beam of light reflected and deflected by the deflector onto an object to be scanned. The present invention relates to a surface tilt correction scanning optical system including a scanning imaging optical system that forms an image.

In addition to the advantage of being able to record at extremely high speeds, laser beam printers have recently become increasingly compact and low-cost, and as office automation equipment diversifies and develops, demand for them is increasing. There is.

For example, in such a laser beam printer, the deflection reflection surface of a deflector such as a polygon mirror used to scan the light beam from the light source may be affected by manufacturing errors, installation errors, vibrations during rotation, etc. There is some tilt error in the direction perpendicular to the scanning plane.

Therefore, the imaging position of the light beam reflected by the deflecting reflection surface having such a tilting error shifts in the sub-scanning direction on the object to be scanned, resulting in uneven scanning line pitch. This pitch unevenness of the scanning lines causes deterioration of the image quality of recording in a recording apparatus such as a laser beam printer, for example.

The above-mentioned surface tilt correction scanning optical system is for eliminating such pitch unevenness of the scanning line, and first, the light beam from the light source is focused in a direction perpendicular to the scanning surface by the linear imaging optical system. The light beam from the deflection reflection point is restored in this direction by the scanning and imaging optical system to form a conjugate image on the object to be scanned. This prevents the influence of the tilting error of the deflection-reflecting surface.

On the other hand, in the scanning plane, in order to make the scanning speed of the beam on the object to be scanned constant, the image height of the beam from the deflection reflection surface is proportional to the angle of incidence on this optical system. An image is formed on the object to be scanned.

Note that in this specification, a scanning plane is a plane formed by a time-series collection of light beams to be scanned, that is, a main scanning line on an object to be scanned, and an optical axis of this surface tilt correction scanning optical system. shall mean a plane containing.

Conventionally, as the above-mentioned surface tilt correction scanning optical system,
Various configurations have been proposed.

An example of this is Special Publication No. 52-28666! [As disclosed herein, the scanning imaging optical system uses a cylindrical lens or the like that once restores and shapes the light beam linearly imaged by the linear imaging optical system into a circular shape after being reflected by a deflector. Some systems include a beam shaping optical system and a converging optical system that converges and images the restored and shaped beam onto the object to be scanned.

In this case, if the beam shaping optical system is configured to restore and shape the ray bundle, the beam shaping optical system will be constrained to restore the beam to a circular beam, thereby achieving uniform speed scanning of the ray bundle. Therefore, the degree of freedom in improving the distortion characteristics provided to the converging optical system and the imaging characteristics on the object to be scanned is reduced. Therefore, in order to obtain a scanning and imaging optical system with excellent properties as described above, many lenses are required, and the configuration of the optical system becomes complicated.

As an improvement, as disclosed in Japanese Patent Laid-Open No. 50-93720, a beam shaping optical system such as the cylindrical lens is interposed between the convergent optical system and the object to be scanned.

In such a configuration, in order to obtain a high-quality image, the beam shaping optical system must be provided close to the object to be scanned. Therefore, this beam shaping optical system needs to be long in the main scanning direction, making it difficult to achieve a compact configuration.

Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 56-36622, a scanning imaging optical system in which a spherical single lens and a single lens having a torrefaction surface are arranged in order from the deflector side is also known. There is. This scanning and imaging optical system has distortion characteristics to obtain uniform speed scanning of the light beam,
It also has the function of correcting the tilting error of the deflection/reflection surface in cooperation with the linear imaging optical system.

However, in this configuration, although the optical system is compact, there are few degrees of freedom due to the configuration, and there is a distortion characteristic to obtain uniform speed scanning of the beam bundle, and a correction function for tilting errors of the deflection and reflection surface. If both of these are maintained in good condition, it is difficult to expand the angle of view by widening the scanning range of the light beam.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to widen the field of view in the main scanning direction while maintaining good imaging characteristics and surface tilt correction function, thereby making the device more efficient. It is an object of the present invention to provide a surface tilt correction scanning optical system that can be constructed more compactly.

In order to achieve this object, the surface tilt correction scanning optical system according to the present invention uses a scanning imaging optical system that images a beam reflected and deflected by a deflector on an object to be scanned, in order from the deflector side. A first lens having a first cylindrical surface having an axis perpendicular to the surface and a second cylindrical surface having an axis perpendicular to the optical axis in the scanning plane, and a second lens having a toric surface are arranged. It is characterized by having been configured.

Note that here and hereinafter in this specification, the toric surface refers to the main scanning direction in which the light beam is scanned in the plane perpendicular to the optical axis of the surface tilt correction scanning optical system, and the main scanning direction in which the light beam is scanned. It means a refractive surface having different refractive powers in the sub-scanning direction orthogonal to the sub-scanning direction.

In addition, a cylindrical surface refers to a refractive surface that has refractive power only in either the main scanning direction or the sub-scanning direction and has no refractive power in the other direction, and is one of the toric surfaces. It is a form.

In the surface tilt correction scanning optical system according to the present invention, by providing the cylindrical surface and the toric surface in separate lenses, the imaging characteristics in the direction perpendicular to the scanning surface can be maintained well over a fairly wide range. This increased the degree of freedom in design. This, in turn, reduces design constraints in the direction along the scan plane, and in this direction,
It maintains good imaging characteristics while having distortion characteristics that can maintain a sufficiently high uniform speed scanning property of the light beam on the object to be scanned,
Moreover, the angle of view can be widened.

Furthermore, the first cylindrical surface having an axis perpendicular to the scanning plane increases the degree of freedom in design in the direction along the scanning plane, and it is possible to favorably maintain uniform speed scanning over a wide angle of view.

Additionally, in the direction perpendicular to the scanning plane, the magnification can be set over a wide range while maintaining a conjugate relationship between the deflection reflection point of the deflector and the imaging point on the object to be scanned with respect to the scanning imaging optical system. . The lower this magnification is, the higher the surface tilt correction effect becomes.

Conversely, the higher the magnification, the better the imaging characteristics tend to be.

Therefore, the magnification can be set in accordance with the required performance.

By increasing the degree of freedom in design, it is now relatively easy to design a small-sized optical system that meets the desired performance. It can now be configured.

Further, according to the present invention, in the second lens, by making the surface opposite to the toric surface a flat or spherical surface, the positioning during processing of the toric surface can be performed accurately, thereby reducing processing effort. It also becomes possible.

In particular, by providing the cylindrical surface of the first lens with negative refractive power in the direction perpendicular to the scanning plane, the imaging characteristics in this direction can be improved over a wide range.

In addition, by providing the second cylindrical surface of the first lens, which has an axis perpendicular to the optical axis in the scanning plane, on the deflector side, and giving this cylindrical surface a negative refractive power, this It is possible to realize an optical system with a wide angle of view, which is highly effective in correcting the surface tilt of the deflection reflection surface of the deflector, which is performed by the negative cylindrical surface and the toric lens of the second lens.

Furthermore, in addition to this configuration, by making the surface of the second lens on the deflector side concave, the distortion aberration imparted in the direction along the scanning plane improves the uniform-velocity scanning performance of the light beam, and the Imaging characteristics in orthogonal directions can be improved.

In addition, by providing the second cylindrical surface of the first lens with negative refractive power on the side of the object to be scanned,
On the object to be scanned, an optical system with good imaging characteristics in a direction perpendicular to the scanning plane over a wide range can be obtained.

Furthermore, the following two conditions must be satisfied in order to maintain good imaging characteristics when carrying out the present invention.

(b) fIH<0 However, fIH: Focal length of the first lens in the direction along the scanning plane This condition mainly applies to the following:
This relates to distortion aberration that is intentionally given in order to obtain uniform speed scanning of a beam of light on an object to be scanned. If this condition is not met, it becomes difficult to maintain good uniform-speed scanning at a wide angle of view, and it is not practical.

(01 If r s/ f + J> 2 However, fIv: Focal length of the first lens in the direction perpendicular to the scanning plane. This condition mainly corrects spherical aberration and field curvature in the direction perpendicular to the scanning plane. It is for the purpose of

If this condition is not met, it is difficult to correct both of the aberrations described above in a well-balanced manner over a wide angle of view. In particular, if the field curvature is not sufficiently corrected, the spot diameter will vary on the scanning line, which will also cause deterioration in image quality.

The present invention will be explained in detail below. The surface tilt correction scanning optical system according to the present invention is, for example, an optical system used in a laser scanning device such as a laser beam printer.

As shown in FIG. 10, the laser scanning device includes a semiconductor laser (1) as a light source, a collimator lens (2), a cylindrical lens (3), a polygon mirror (4), an fθ
It is composed of a lens (5), a photosensitive drum (6), and the like.

A laser beam (B) that is directly modulated according to image information is emitted from the semiconductor laser (1), and this laser beam (B), which is an example of a ray bundle, is emitted by the collimator lens (2).
The light is shaped into parallel light. Thereafter, the light is once converged linearly by a cylindrical lens (3), which is an example of a linear imaging optical system, and is imaged on a deflection reflection surface (4a) of a polygon mirror (4), which is an example of a deflector. This deflection reflecting surface (4a)
The laser beam (B) after being reflected is deflected by the rotation of the polygon mirror (4), and is directed to the photoreceptor drum (6) by the fθ lens (5), which is an example of a scanning imaging optical system.
An image is formed above and scanned in the direction A in the figure.

The surface tilt correction scanning optical system is the linear imaging optical system (3) described above.
) and a scanning imaging optical system (5) consisting of two lenses (Gl) and (G2), and the pitch of the scanning line caused by the tilting of the deflection reflecting surface (4a) of the deflector (4). This is to remove the misalignment. Specifications of an embodiment showing a specific configuration of the scanning imaging optical system (5) are shown below.

There are three examples, each corresponding to the lens configuration diagrams shown in FIGS. 1 to 3 and the aberration diagrams shown in FIGS. 4 to 9. Table 1 below summarizes the correspondence relationships.

In each lens configuration diagram in Table 1, (a) shows the lens arrangement cut along the scanning plane, and (r+) shows the lens arrangement cut along the plane perpendicular to the scanning plane. . Note that the mark [*] next to the symbol of the reflective surface indicates a cylindrical surface, and the symbol [**] indicates a toric surface. In addition,
The symbol of the lens surface and the distance between the axial surfaces are shown in (
Only the lens configuration diagram (a) will be shown, and in the lens configuration diagram (rl), illustrations other than those that are different will be omitted.

In addition, in the aberration diagram in the direction along the scanning plane, the distortion aberration is defined as the ideal image height for obtaining constant-velocity scanning of the beam of light. Angle f with the optical axis: This is the focal length of all scanning and imaging optical systems in the direction along the scanning plane, and is expressed as a percentage of the deviation of the actual image height from this ideal image height as shown by the following formula.

((y'-fθ) / fθ) refractive index [at 780 nm] n2: refractive index of the optical material constituting the second lens (G2) [at 780 nm] fl, l: focal length of the first lens (G1) in the direction along the scanning plane Lv: scanning Focal length of the first lens (G1) in the direction perpendicular to the surface (Example 1) f=125. F pottery 5012ω=971f+H=
271.251 flv = 100.117
fl, I/Lv-2,71 <Example 2> f=125. F 50, 2ω=97°fu+=
996.16 flv = 15.484 f
l, Iz'f+v=64.33 (Example 3) f=125.Fllh50.2ω=97'LH=
-255,78fly” 62.490 ft+<
/Lv=4.09

[Brief explanation of the drawing]

The drawings show embodiments of the surface tilt correction scanning optical system according to the present invention, and FIGS. 1 to 3 are lens configuration diagrams of each embodiment,
(A) in FIGS. 1 to 3 is a lens configuration diagram cut in a direction along the scanning plane, and (B) in FIGS. 1 to 3 is a lens configuration diagram cut in a direction perpendicular to the scanning plane. Figures 4 to 6 are aberration diagrams in the direction along the scanning plane in each embodiment, Figures 7 to 9 are aberration diagrams in the direction perpendicular to the scanning plane in each embodiment, and Figure 10 is the laser beam 1 is a schematic configuration diagram of a scanning device of a printer. (1)...Light source, (3)...Linear imaging optical system, (4)...Deflector, (4a)...
...Polarizing reflective surface, (5)...Scanning imaging optical system,
(6)...Scanned object, (B)...Light ray bundle, (G1)...First lens, (G2)...
...Second lens.

Claims (6)

[Claims] (1) A linear imaging optical system that forms a linear image of a beam of light emitted from a light source onto a deflection reflection surface of a deflector, and forms an image of a beam of light reflected and deflected by the deflector onto an object to be scanned. A surface tilt correction scanning optical system comprising: a scanning imaging optical system, the scanning imaging optical system comprising, in order from the deflector side, a first cylindrical surface having an axis perpendicular to the scanning surface; A surface tilt correction scanning optical system configured by arranging a first lens having a second cylindrical surface having an axis perpendicular to the optical axis in the plane, and a second lens having a toric surface. (2) The surface tilt correction scanning optical system according to claim 1, wherein the first lens has negative refractive power in a direction perpendicular to the scanning surface. (3) The surface tilt correction scanning optical system according to claim (2), wherein the second cylindrical surface is located on the deflector side of the first lens and has negative refractive power. system. (4) Surface tilt correction scanning according to claim (2), wherein the second cylindrical surface is located on the object side of the first lens and has negative refractive power. Optical system. (5) Claims (1), (3), or (4), wherein the first lens has negative refractive power in the direction along the scanning plane. Scanning optical system with surface tilt correction. (6) A surface tilt correction scanning optical system according to any one of claims (2) to (5), wherein the first lens satisfies the following conditions. |f_1_H/f_1_V|>2 However, f_1_H: Focal length of the first lens in the direction along the scanning plane f_1_V: Focal length of the first lens in the direction perpendicular to the scanning plane