JPS6353512A - Scanning optical system for correcting surface inclination - Google Patents

Abstract

PURPOSE:To make the field angle wider in the main scanning direction, by providing a 1st lens having a toric surface on a deflector side and a 2nd lens having a toric surface on an object to be scanned side. CONSTITUTION:A scanning and image forming optical system is constituted by providing the 1st lens G1 having a toric surface on a deflector side and the 2nd lens G2 having a toric surface on an object to be scanned side in the order from the deflector side. By installing the two toric surfaces to the lenses G1 and G2 respectively, the image forming characteristic in the direction intersecting the scanning plane at right angles can be maintained excellently over a considerably wider range and the degree of freedom in designing is increased. Therefore, restriction in designing in the direction along the scanning plane can be reduced and the image forming characteristic can be maintained excellently and the field angle can be made wider while a distortion characteristic which can maintain the uniform-speed scanning property of a bundle of rays of light on an object to be scanned at a sufficiently high level is maintained.

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 pinch unevenness of the scanning line causes a deterioration in 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.

As an example, as disclosed in Japanese Patent Publication No. 52-28666, a scanning imaging optical system uses a linear imaging optical system to form a linear image of a light beam, and after reflection by a deflector, Some beam shaping systems include a beam shaping optical system such as a cylindrical lens that once restores and shapes the beam into a circular shape, and a convergent optical system that converges and images the restored and shaped beam onto an object to be scanned.

In this case, if the beam shaping optical system is configured to restore and shape the beam, a constraint will be imposed on the beam shaping optical system to restore the beam to a circular beam. In order to achieve this, 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 the above-mentioned excellent characteristics as a scanning imaging optical system, many lenses are required, and the structure 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 Laid-Open No. 56-36622, a scanning imaging optical system in which a spherical single lens and a toric surface single lens 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 includes a scanning imaging optical system that images a beam reflected and deflected by a deflector onto an object to be scanned. The present invention is characterized in that a first lens having a toric surface on the device side and a second lens having a toric surface on the moving image to be scanned are arranged.

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

And, because the degree of freedom in design has been increased in this way,
It has become relatively easy to design a small optical system that meets the desired performance, and it has become possible to make the optical system wider and more compact.

In particular, by making the toric surface of the first lens concave toward the deflector both in the direction along the scanning plane and in the direction orthogonal to the scanning plane, imaging in each direction can be achieved over a wider range. The characteristics can be further improved.

Furthermore, in the first lens and the second lens, respectively,
By making the surface facing the toric surface a flat surface, it is possible to accurately position the toric surface during machining, thereby reducing the labor involved in machining.

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

(b) r1v/r4v≦1 However, rlv: radius of curvature of the side surface of the deflector of the first lens in a direction perpendicular to the scanning surface r4v: radius of curvature of the second lens on the side surface of the object to be scanned in a direction perpendicular to the scanning surface The conditions are mainly for correcting spherical aberration and field curvature in the direction perpendicular to the scanning plane.

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, leading to deterioration in image quality.

(o) 0.3<(d,+d3)/f<0.5 However, d - axial distance on both sides of the first lens d3 = axial distance on both sides of the second lens f: Along the scanning plane This condition is primarily defined by the focal length of all scanning imaging optics in the direction along the scan plane.
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, making it impractical.

Specifically, if the lower limit of the conditional expression is exceeded, it becomes difficult to correct the uniform speed scanning property, and if the upper limit is exceeded, the entire system becomes large and cannot be configured compactly.

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. 16, 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 surface tilt of the deflection reflection 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 five examples, each corresponding to the lens configuration diagrams shown in FIGS. 1 to 5 and the aberration diagrams shown in FIGS. 6 to 15. Table 1 on the next page shows all the correspondence relationships.

In each lens configuration diagram in Table 1, (A) shows the lens arrangement cut along the scanning plane, and (El) 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 toric surface. Note that the symbols of the lens surfaces and the distances between the axial surfaces are shown only in the lens configuration diagram in (a) of each embodiment, and are omitted in the lens configuration diagram in (b) except for those that are different.

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 uniform speed scanning of the beam of light. Angle r with the optical axis: 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)xloo(%) However, y゛: Actual image height and other specifications of each example, 2ω: Maximum angle of incidence n,: Optical elements constituting the first lens (G1) Refractive index of material [at 780 nm] n2; Refractive index of optical material constituting the second lens (G2) [at 780 nm] <Example 1> f=125. F 50, 2ω-97°r1v/r4
v=0.867 (tL+dt)/f=0.4
27 <Example 2> f=125. F 50, 2ω = 97°r1v/rn
v=0.300 (d++d3)# =0.387〈
Example 3> f=125. F floor 50, 2ω = 97°rlv/r4
V=o, sot (tL+d3)/f =0.419
<Example 4> f=125. FNa50. 2ω=97°r1v/
r4v=0.865 (rL +dz)/f=0.
426 (Example 5) f=125. F 50, 2ω-97"r1v/r4
v=0.672 (a+ +#, l)#-Te0.39
0

[Brief explanation of drawings]

The drawings show embodiments of the surface tilt correction scanning optical system according to the present invention, and FIGS. 1 to 5 are lens configuration diagrams of each embodiment.
(A) in FIGS. 1 to 5 is a lens configuration diagram cut in the direction along the scanning plane, and (υ) in FIGS. 1 to 5 is a lens configuration diagram cut in the direction perpendicular to the scanning plane. Figures 6 to 10 are aberration diagrams in the direction along the scanning plane in each embodiment, Figures 11 to 15 are aberration diagrams in the direction perpendicular to the scanning plane in each embodiment, and Figure 16 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 flux, (G1)...First lens, (G2)...
...Second lens.

Claims (5)

[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, wherein the scanning imaging optical system includes, in order from the deflector side, a first lens having a toric surface on the deflector side; A surface tilt correction scanning optical system configured by disposing a second lens having a toric surface on the side of the object to be scanned. (2) The problem described in claim (1), wherein the toric surface of the first lens is concave toward the deflector in both the direction along the scanning plane and the direction perpendicular to the scanning plane. Erase correction scanning optical system. (3) The surface tilt correction scanning optical system according to claim 1, wherein the side surface of the object to be scanned of the first lens is a flat surface. (4) The surface tilt correction scanning optical system according to claim 1 or 2, wherein the side surface of the deflector of the second lens is a flat surface. (5) The surface tilt correction scanning optical system according to any one of claims (1) to (4), wherein each surface of the first lens and the second lens satisfies the following conditions. system. (a) r_1_v/r_4_v≦1 (b) 0.3<(d_1+d_3)/f<0.5, however, r_1_v: radius of curvature of the side surface of the deflector of the first lens in a direction perpendicular to the scanning plane r_4_v: second lens Radius of curvature d_1 of the side surface of the object to be scanned in the direction perpendicular to the scanning plane: Distance between the axial surfaces of both side surfaces of the first lens d_3: Distance between the axial surfaces of both side surfaces of the second lens f: All in the direction along the scanning plane focal length of the scanning imaging optics